Patent Publication Number: US-7584298-B2

Title: Topology aware route control

Description:
CROSS-REFERENCES TO RELATED REFERENCES 
     This application claims priority to U.S. Provisional Application No. 60/433,285 entitled “Topology-Based Route Control Over Data Networks Using Convergence Point Analysis” filed Dec. 13, 2002, which is incorporated herein by reference. 
     This application also incorporates each of the following by reference for all purposes: 
     U.S. Non-Provisional Application entitled, “Data Network Controller,” having U.S. patent application Ser. No. 10/286,576 and filed Nov. 1, 2002, published as U.S. Patent Publication Number U.S. 2003/0088529 A1; 
     U.S. Non-Provisional Application entitled, “System and Method to Assure Network Service Levels with Intelligent Routing,” having U.S. application Ser. No. 09/833,219 and filed Apr. 10, 2001, now issued as U.S. Pat. No. 7,269,157; 
     U.S. Non-Provisional Patent Application entitled, “System and Method to Provide Routing Control of Information Over Data Networks,” having U.S. patent application Ser. No. 10/013,809 and filed Dec. 7, 2001, now issued as U.S. Pat. No. 7,222,190; 
     U.S. Non-Provisional Patent Application entitled, “System and Method to Provide Routing Control of Information over Networks,” having U.S. patent application Ser. No. 10/040,902 and filed Dec. 28, 2001, now issues as U.S. Pat. No. 7,133,365; and 
     U.S. Provisional Patent Application entitled, “System and Method to Assure Network Service Levels and Bandwidth Management with Intelligent Routing,” having U.S. Provisional Patent Application No. 60/350,186 and filed Nov. 2, 2001. 
    
    
     BACKGROUND 
     The present invention relates generally to the control of data over network communications systems, and more specifically to topology-based route control of data over communications networks. 
     Networks are communications systems that connect nodes or points for the purpose of sharing resources. A node typically represents a computer or collection of computers or other computing devices. Interchangeably referred to herein as a “point,” a node is typically an endpoint for a particular segment along a network “path” or “route.” A route describes a path between two nodes which may or may not encompass intermediate nodes, connections, sub-routes and the like between a data source, such as a web-based database, and a destination, such as a customer, partner, or branch website. 
     Networks typically represent a topology of devices and connections such as computers, servers, peripheral equipment, and other computing devices, connected by cables, wires, or other communication media for use in transmitting data and information in the form of electronic signals, for example. Networks may be classified in a number of ways, including nodal and topology. Nodes can be classified as servers, computers, or other types of computing devices and typically include routers, hubs, and switches. Networks can also be classified according to the topology of the network. 
     Under topology-based classifications, networks are classified by the configuration of the network equipment and components. Star, bus, ring, and hybrid configurations are representative network configurations well known in the art. Another topology-based classification relates a particular type of network to a number of aggregated devices associated therewith. 
     For example, over a short-distance, such as within a building or small cluster of buildings, a Local Area Network or LAN can be used. Where computing resources are spread over a larger area, such as a city or town, a Metropolitan Area Network or MAN may be used. Computers, servers, routers, switches, and hubs are representative of some types of equipment that are networked for the purpose of sharing with other users, regardless of the type of network. However, networks over large geographic areas are generally classified as Wide Area Networks or WANs. WANs can also connect LANs or other WANs thus forming larger networks encompassing more users and branch offices. 
     One particular data network is the Internet, which is increasingly being used as a method of transport for communication of resources between companies and consumers. Information technology or “IT” is used by many types of organizations and businesses to manage data transport over data networks. Sharing of information, data, and other resources is a mission-critical activity in many organizations. Software programs (i.e., “applications”) that share data or information over networks permit increased efficiencies, dramatic lowering of associated costs, and improvement in overall performance. However, performance bottlenecks have emerged over time, limiting the usefulness and efficiency of the Internet infrastructure for business-critical applications. These bottlenecks occur typically at distinct places along the many network routes to a destination from a source, for example. Each distinct bottleneck requires a unique solution and they may occur at various places along a network route. 
     Conventional route control techniques and technologies utilize and make control decisions on data routes as advertised from a current or in-use routing table. These routes are often large allocations of address space meant to keep an inter-provider routing table small. Aggregation of routes is a criterion when routing tables are communicated among large Internet service providers (ISPs), as is common when using data routing protocols such as Border Gateway Protocol (BGP). 
     With the introduction of classless inter-domain routing (CIDR), a routing table is established using a variety of network sizes. For example, a network may have numerous IP addresses, such as a corporate LAN. The network (or a group of such networks) is listed in a routing table as a network prefix. A prefix can be, for example, a 32 bit IP address that has an associated netmask indicating how many of the leading bits are significant. 
     BGP4 is a version of a protocol deployed to handle variable length prefixes introduced with CIDR. With BGP4, a prefix is no longer required to be defined by a byte boundary (Class A, B, or C space), but can be one of 32 different sizes depending on the length of the network mask. The common notation for a prefix is “address/netmask”, e.g. 12.0.0.0/8. The 12.0.0.0 is the address and the “/8” indicates that only the first 8 bits of that address are significant such that, in this case, the “12” is a prefix defining the associate address space. The fewer the bits in the netmask, the more IP addresses in the prefix. For example, a /16 prefix has 256 times the address space of a /24 prefix given the 8 bit difference in the netmask. 
     Traditional route control products utilize and make control decisions on routes as advertised in a BGP routing table. These routes are often described as large allocations of address space intended to reduce the size of an inter-provider routing table. These route control products, however, do not consider the vast geographic distances that may exist between adjacent networks of a large address block. This is relevant to a multi-homed enterprise which may have geographically disparate branch offices or network server locations in, for example, California, Maryland, Florida, and Texas. Conventional route control products do not efficiently route data to multi-homed enterprises, often degrading performance by selecting the shortest path to a destination address. 
     Further, conventional routing control products force users to make a route control decision that improve some portions of the address space at the expense of possibly degrading other portions of the address space related to a second geographic region. Potentially, conventional products may not be aware of an address distribution and users consequently confront control decisions that can introduce larger problems than those resolved by limited route control decisions. 
     As will be described below in connection with  FIG. 1D , address allocations in a single aggregated route can fall into widely different locations. In this figure, one of the address allocations occurs in San Jose (12.0.128.0/1) and another in New York (12.0.0.0/1). It is uncommon that a single route decision for the /16 can effectively optimize every address in the block. Users may face performance degradations at some destinations in order to optimize performance at other destinations because conventional routing control products do not adjust for multi-homed network configurations. Alternatively, users may fail to recognize this geographic diversity, not realizing a large-scale route (e.g., a /16 route) may be geographically widespread and thus direct data routing in an inefficient manner. Upon fixing small problems for a particular destination will introduce greater problems for a larger set of destinations. If the cascading problems are not recognized, the product may then introduce performance route flapping for a large address block. In conventional route control techniques, control decisions on routes in a routing table move large volumes of traffic between two NSPs. The delivery of high volumes of advertisements can significantly disrupt multi-homed enterprise networks. 
     In the field of data communications, the line of signal transmission from a source to a destination traverses a “first mile,” a “middle mile,” and a “last mile,” the latter of which can be located at either end of a data path, typically connecting the switch or central office of a telecommunications service provider such as Pacific Bell to a customer&#39;s PBX. In one particular segment, the “last mile,” a bottleneck has received attention over the past few years. The “last mile” is the connection between end-users and a communications network, such as a connection from a central office to a home subscriber or user. Systems such as xDSL and cable access using coaxial cable have emerged to dramatically improve last mile performance. As described herein, the “first mile” bottleneck is part of the network where content is hosted on Web servers. First mile access has improved, for example, through the use of more powerful Web servers, higher speed communications channels between servers and storage, and load balancing techniques. 
     The “middle mile,” however, is the last bottleneck to be addressed in the area of Internet routing and the most problematic under conventional approaches for resolving such bottlenecks. The “middle mile,” or core of the Internet, is composed of widespread telecommunications networks known as “backbones.” “Peering points” are nodes where the backbone networks are joined together. Peering points have been under-built structurally and tend to be areas of congestion for data traffic. Conventional data pathing problems over backbone networks and peering points include routing delays and latencies, transmission obstacles or obstructions, authentication and security filtering, filtered addresses, and other forms of data congestion. Generally no incentives exist for backbone network providers to cooperate to alleviate such congestion. Given that over about 95% of all Internet traffic passes through multiple networks operated by network service providers, just increasing core bandwidth and introducing optical peering, for example, will not provide adequate solutions to finding an efficient data route or path between a data source and a destination. 
     Peering is when two Network Service Providers (“NSPs”), or alternatively two Internet Service Providers (“ISPs”), connect in a settlement-free manner and exchange routes between their subsystems. For example, if NSPI peers with NSP 2  then NSPI will advertise only routes reachable within NSPI to NSP 2  and vice versa. This differs from transit connections where full Internet routing tables are exchanged. An additional difference is that transit connections are generally paid connections, peering points are generally settlement-free. That is, each side pays for the circuit, or route, costs to the peering point, but not beyond. Although a hybrid of peering and transit circuits (i.e., paid-peering) exist, only a subset of full routing tables are sent and traffic sent into a paid-peering point generally does not affect a route change, thus increasing the volume of data transmitted and hindering route control. 
     Routes received through peering points are defined as a single AS away from a BGP routing perspective. That makes these routes highly preferable by BGP (and by the provider because the connections are cost-free). However, when there are capacity problems at a peering point and performance through it suffers, traffic associated with BGP still passes through the problematic peering point and thus, the end-to-end performance and routing of all data traffic will suffer. 
     Structurally, the Internet and its peering points include a series of interconnected network service providers. These network service providers typically maintain a guaranteed performance or service level within their autonomous system (AS). Guaranteed performance is typically specified in a service level agreement (“SLA”) between a network service provider and a user. The service level agreement obligates the provider to maintain a minimum level of network performance over its network. The provider, however, makes no such guarantee with other network service providers outside their system. That is, there are no such agreements offered across peering points that link network service providers. Therefore, neither party is obligated to maintain access or a minimum level of service across its peering points with other network service providers. 
     Invariably, data traffic becomes congested at these peering points and inefficient data paths result. And since, the Internet path from end-to-end is generally unmanaged, uncontrolled, and typically inefficient, the Internet can occasionally be a non-optimal data transport mechanism for mission-critical applications. Moreover, other factors exacerbate congestion such as line cuts, planned outages (e.g., for scheduled maintenance and upgrade operations), equipment failures, power outages, route flapping and numerous other phenomena in addition to those problematic effects mentioned above. 
     In some common approaches, it is possible to determine the service levels being offered by a particular network service provider. This technology characterizes candidate paths in which to route data over and includes at least two types. Active probes are the first type, which are near real-time active calibration of the data path, using tools such as ICMP, traceroute, Sting, and vendors or service providers such as CQOS, Inc., and Keynote, Inc. Another traditional approach is real time passive analysis of the traffic being sent and received, utilizing such tools as TCPdump, and vendors such as Network Associates, Inc., Narus, Inc., Brix, Inc., and P-cube, Inc. A significant drawback of these conventional methods of passive analysis of data traffic flow, however, is that these systems are not “topologically” aware of the various networks, peering points, nodes, and network conditions that can affect data route control. Consequently, conventional systems cannot readily adjust to changing environmental network conditions to select an optimized data path between particular nodes, without employing large amounts of probing. In other words, candidate paths cannot be assessed in near real-time to determine availability of alternative routes based upon a change in the network topology. 
     Traditional route control techniques rely on probes or other additional traffic to be transmitted over the network to provide candidate path information to form the basis of an intelligent route update. Active probing relies upon the use of numerous probes being sent to individual destination IP addresses. This results in increased amounts of traffic that contribute to network degradations by lowering data routing efficiency. This additional data traffic over large scale deployments, can clog nearby network circuits, is difficult to configure and maintain, and causes potential security notifications near a remote probe destination. These notifications result in administrative overhead due to interactions with the remote security departments. Common probing methods include but are not limited to ICMP Echo Request (ping), Traceroute, TCP probes, UDP probes, and embedded content probes initiating measured HTTP GET Requests for that content. By using probes to determine network degradations, additional data traffic further retards the efficiency of particular data routes, slowing mission-critical data applications and resulting in excessive costs. 
     Traditional route control techniques generally routes data based on prefix lengths that exist in an Internet routing table such as a prefix length of /24. These advertisements are not topologically aware, that is they do not know, in a geographic sense, where the destinations are located. The length of the prefix describes the level of specificity of a particular address for a “node” or point along the network. Advertisements or announcements are generated by conventional data flow and route control systems to “advertise” or “announce” a particular data path, from routing information received in response to probes. If the prefix length is short (/19 or shorter), this can result in a single advertisement affecting data traffic to multiple geographically diverse destinations. In other words, an advertisement or announcement for a shorter prefix length will direct data traffic to an increased number of multiple nodes or points, as opposed to the use of a longer prefix length that directs data traffic to specific points. With the increased number of multiple nodes over which data is sent, the more susceptible a shorter prefix is to geographically-related problems. However, using arbitrarily long prefix lengths such as /24 can result in many specific advertisements to numerous specific destinations to solve a single problem. 
     In particular, inefficient data routing and control can lead to significant expenses as high rates and volume of data are often metered on a per unit basis. In other words, a company using an internet or network service provider that enables access for data traffic over telecommunications networks may assess charges based upon data throughput, data volume, or time-connection charges. Greater data traffic and usage will result in higher costs charged to the organization providing the data. In an organization where tremendous amounts of data traffic need to be routed to destination sources, costs may become too expensive to efficiently use active probes without significantly increasing data volume. Further, if time and network condition-sensitive applications are used among distributed and/or multi-homed enterprises, then inefficient route control will result in significant costs and lowered financial performance within an organization. Another significant disadvantage associated within conventional data route control techniques is cost. 
     Another common problem with active probes is the impact they can have on the remote destination, especially with respect to security policy. Given the volume of active probes that often must be sent to collect sufficient performance information, these active probes can often be mistaken for denial of service attacks. Often times the port numbers used by the active probes can be mistaken for a port scan. These common Internet “attacks” are often detected automatically by security devices such as firewalls and intrusion detection systems. Often these devices are not sophisticated enough to distinguish a harmless network probe from a legitimate attack. As such, route control can often trigger false security alarms at the destination being optimized. This results in administrative overhead in handling security alerts incurred as a result of the probing. 
     Yet another drawback to conventional route control technique is that existing networks must be configured to allow the probes to override default routing behavior. A network engineer is forced to configure all existing network infrastructure to support probe based route control. Such configurations require increased manpower to accomplish. In addition, as the underlying network changes, the configuration of the route control probes may need to change along with it, thus creating maintenance overhead costs. 
     Still another drawback to common approaches to route control include the unrestricted use of active probes. These probes represent excessive additional traffic and increased overhead costs in sending data over a network. This overhead can be significant if the number of destinations being probed is large. For example, common probe techniques for 10,000 destinations can fill an entire T1 circuit. This overhead is wasted bandwidth that is not communicating relevant application information. 
     Therefore, what is needed is the ability to optimize network and route control performance without compromising performance by directing data to meet address allocations requirements. In other words, what is needed is a system and method of topology-based route control that can determine candidate paths for data traffic with minimal increases in data traffic volume, minimal effects on network security, and minimal maintenance and overhead costs. Moreover, what is needed is a system and method that can adapt data paths or paths in response to changes in a network topology. 
     SUMMARY 
     The present invention meets the needs described above by providing topology aware route control. In particular, the present invention uses proxy points for measuring different routes so that measurements are more accurate and can be meaningfully compared. Traditional route control techniques are based upon end-to-end measurements or measurements that are essentially end-to-end, i.e. within one or two hops of the end. A drawback of using end-to-end measurements is that the measurements can be misleading. For example, comparing end-to-end measurements of two paths that share a significant non-diverse section does not provide a valid comparison because the portion of the measurements related to the non-diverse section distorts the comparison. 
     In contrast the present invention uses proxy points to eliminate or minimize the inclusion of a non-diverse section. The terms proxy point, probe point and convergence point are used interchangeably herein. A proxy point is a point that is used instead of an end point to measure a path. In one aspect of the invention, the proxy point is a convergence point. In other aspects of the invention the proxy point is identified using other intermediate hops on the data path, common addresses inside a destination address block, such as the broadcast address, well-known common network infrastructure elements, such as DNS servers or gateway routers, or techniques such as triangulation of third-party measurements. A proxy point can be any intermediate point between the source and the end point and includes a point that is N−1 hops from the end point. 
     Convergence point analysis represents a simple and effective method of identifying proxy points. Convergence point analysis can run using only local information and can identify proxy points that are more specific than other methods. In addition, convergence point analysis is effective in identifying path diversity. With convergence point analysis, the eventual measurements to the identified proxy point are the most accurate while still obtaining all of the benefits that measurement proxies entail (security, aggregation, accuracy, relevance, diversity). However, the invention is not limited by the method used to identify the proxy points, as all methods deliver some, if not all, of the benefits mentioned above. 
     In one aspect of the invention that uses convergence points, multiple paths are identified to the desired destination address space. Each path begins at a source and terminates at the destination address space. The source can be associated with a router, an entity or a location. The paths can be identified using active path trace probes in connection with a passive flow analyzer. Convergence points are identified either as the paths are identified or once each path is identified. A convergence point is a point or a node where two or more paths converge. Beyond the convergence point the paths are non-diverse. 
     Once a convergence point is identified the path performance from each source to the convergence point is measured and compared. Because the measurements are to the convergence point rather than to the destination address space, the measurements reflect the performance of the diverse portions of the different paths. Based on the measurements, an optimum route or path is identified. The measurements of the path performances can be performed periodically so that the routing can be dynamically changed as network conditions change. 
     To further optimize routing, the address spaces associated with the convergence point can be aggregated. The identification of the paths provide information regarding the topology of the network. This information can be used to aggregate address space. Specific addresses associated with a single convergence point are compared to determine which addresses can be aggregated. In some aspects of the invention, it is possible to aggregate specific addresses associated with different convergence points so long as the paths to the specific addresses share a common next hop. 
     In another aspect of the invention that uses proxy points that are identified using DNS servers, third-party measurements or any other identification methods, multiple paths are identified to the desired destination address space. Each path begins at a source and terminates at the destination address space. Proxy points are identified either as the paths are identified or once each path is identified. A proxy point is a point between the source and the destination address space. Different proxy points can be associated with different paths. Preferably the proxy point is located within the middle mile of the path. 
     Once the proxy points are identified the path performances from each source to the appropriate proxy point are measured and compared. Based on the measurements, an optimum route or path is identified. The measurements of the path performances can be performed periodically so that the routing can be dynamically changed as network conditions change. As with the aspect using convergence points, address aggregation is possible. 
     These and other aspects, features and advantages of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an exemplary computer system for presenting to a user a user interface suitable to practice an embodiment of the present invention; 
         FIG. 1B  shows basic subsystems in the computer system of  FIG. 1A ; 
         FIG. 1C  is a generalized diagram of one exemplary computer network suitable for use with the present invention; 
         FIG. 1D  depicts a typical data network using multi-path; 
         FIG. 1E  illustrates a simplified data network and flow control system in accordance with a specific embodiment of the present invention; 
         FIG. 2  is a simplified block diagram of one embodiment of a flow control system according to one embodiment the present invention; 
         FIG. 3  is a functional block diagram of an exemplary passive calibrator of  FIG. 2 ; 
         FIG. 4  is a functional block diagram of an exemplary content flow analyzer of  FIG. 3 ; 
         FIG. 5  is a functional block diagram of an export flow analyzer of  FIG. 3  in accordance to one embodiment of the present invention; 
         FIG. 6  is a functional block diagram of a passive flow analyzer of  FIG. 3  according to a specific embodiment; 
         FIG. 7  is a simplified timing diagram of determining network performance metrics with an exemplary flow control system located near a client or a source; 
         FIG. 8  is a simplified timing diagram of determining network performance metrics with an exemplary flow control system located near a server or a destination; 
         FIG. 9  is a network diagram of an exemplary passive calibrator with distributed packet capture according to another embodiment of the present invention; 
         FIG. 10  is a network diagram of distributed passive flow elements according to yet another embodiment of the present invention; 
         FIG. 11  is a functional block diagram of the distributed passive flow elements of  FIG. 10  according to still yet another embodiment of the present invention; 
         FIG. 12  is a detailed block diagram of an exemplary usage collector according to a specific embodiment of the present invention; 
         FIG. 13  is a block diagram of a routing server using an associated configuration element receiving one or more protocol feeds, according to one embodiment of the present invention; 
         FIG. 14  is a graphical representation illustrating an exemplary method to determine the amount of bandwidth available that can be used without additional cost in accordance to the present invention; 
         FIG. 15  is a graphical representation illustrating an exemplary method to calculate billable rates in accordance to the present invention; 
         FIG. 16  is a graphical representation depicting an exemplary method to calculate billable rates using short range forecasting in accordance to the present invention; 
         FIG. 17  is a representation of an exemplary address or prefix list according to an embodiment of the present invention; 
         FIG. 18  illustrates an exemplary embodiment of a simplified data network path illustrating three data paths through several network service providers in accordance with the present invention; 
         FIGS. 19A ,  19 B,  19 C,  19 D,  19 E, and  19 F, collectively  FIG. 19 , illustrate network topologies including convergence points and destinations in accordance with an exemplary embodiment of the present invention; 
         FIGS. 20A ,  20 B, and  20 C, collectively  FIG. 20 , are a further illustration of  FIG. 19 , with five destination subnetworks associated with IP address prefixes of 24 bit length in accordance with an exemplary embodiment of the present invention; 
         FIGS. 21A and 21B , collectively  FIG. 21 , are graphical representations illustrating an exemplary data structure for relating convergence point information to address space in accordance with a specific embodiment of the present invention; 
         FIG. 22  is a flowchart depicting an exemplary method of collecting path trace information to determine convergence points in accordance with a specific embodiment of the present invention; 
         FIG. 23  is a flow chart illustrating an exemplary method for path trace measurement for determining whether a probe point in a data network is a convergence point in accordance with an exemplary embodiment of the present invention; 
         FIG. 24  is a graphical representation illustrating another exemplary data structure for relating convergence point information and next-hop information to an address space in accordance with another specific embodiment of the present invention; 
         FIG. 25  is a block diagram of an exemplary system for routing data over one or more networks based on convergence point analysis in accordance with a specific embodiment of the present invention; 
         FIG. 26  illustrates an exemplary routing table according to a specific embodiment of the present invention; 
         FIG. 27  illustrates a graphical representation of a four-NSP prefix distribution of convergence point analysis information, in accordance with an embodiment of the present invention; 
         FIG. 28  illustrates a network topology for path trace measurement and analysis and a path trace report, in accordance with an embodiment of the present invention; 
         FIG. 29  illustrates a path diversity report, in accordance with an embodiment of the present invention; 
         FIG. 30  illustrates a path length report, in accordance with an embodiment of the present invention; and 
         FIG. 31  illustrates a destination distance and traffic volume report, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed descriptions of specific embodiments of the present invention are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, method, process or manner. 
     The present invention relates generally to routing of data over networked communication systems, and more specifically to a system and method for topology-based route control over data networks using, for example, convergence point analysis. Some embodiments of the present invention utilize network topology information to pinpoint the precise location of middle-mile performance problems and target route control decisions that affect only an address space, or a subset thereof, experiencing performance problems. Data transmission in a network uses protocols to standardize sharing of resources between communications devices. Border Gateway Protocol (BGP) is such a protocol that is used between autonomous networks, particularly multi-homed networks (i.e., networks that rely upon more than one service provider to access the Internet). In many instances, data routing relies upon the use of protocols such as BGP. Other examples of protocols include Exterior Gateway Protocol, Transmission Control Protocol/Internet Protocol (TCP/IP), RIP v2, EIGRP, and the like can be used to standardize communication among data networks. 
     Specific embodiments of the present invention analyze nodes along data routes using convergence point analysis. Convergence point analysis, using active probing techniques and passive data analysis, can construct efficient data routes or “paths” between a source and a destination. By probing nodes or points, the present invention can assemble an efficient data route from responsive information received and stored in response to active probes. Embodiments of convergence point analysis and route control techniques employing a specific embodiment of the invention will be described in greater detail below. 
     In some embodiments of the present invention, segments of a data route (e.g., the intermediate route between two consecutive nodes) between two consecutive nodes form a “hop” and one or more hops can compose a data route. Data routes can also be referred herein as “paths.” Nodes where two or more data routes converge are herein referred to as “convergence points.” Using some embodiments of the present invention, efficient data routes can be constructed from data generated by analyzing convergence points, as described herein. Convergence points are analyzed for network degradations that may reduce the efficiency of a particular data route. Network degradations such as transmission latencies, missing/damaged/offline network equipment, line breaks, filtered addresses, security firewalls, and the like may render a particular route prohibitively expensive and inefficient to use when routing data. 
     The present invention increases the efficiency of routing data between a source and a destination point and vice versa over a network by adjusting a data route with near-real time frequency. Topological maps are created by embodiments of the present invention using data stored in a repository (e.g., characteristics of nodes such as IP addresses, latency, RTT, etc.), received in response to active probes generated by a system in accordance with one embodiment of the present invention. By probing convergence points and, if necessary, sub-convergence points, some embodiments of the present invention can establish a topological map by which efficient data routes can be constructed and modified in near real-time. 
     A data path as described herein can be a route, or path, from a first point (e.g., source) to a second point (e.g., destination), and is divided into path portions or “hops,” each of which connects two or more peering points or nodes along a contiguous path between a source and a destination point. Data control techniques generally use address prefix lengths that exist in a routing table, typically identified using length designations such as “/24.” The longer the prefix, the more specific the address. A /19 prefix represents an address space that is a larger subset of addresses than that of a /24 prefix. If a problem occurs with an address with a /19 prefix, a larger number of addresses would be affected than a point with a prefix of /24. Thus, a /19 prefix would affect more destinations and/or addresses than a /24 prefix. Such techniques assign arbitrary-length prefixes to route announcements. By creating topological network maps using convergence point analysis some embodiments of the present invention, as described below, permit fewer announcements to be used, but with greater specificity. Thus, data traffic volume is reduced and the efficiency of data routing and control is improved. 
     Although the term “prefix” is used herein to describe the subdivision of IP addresses into one or more address spaces, it is noteworthy that the present invention is not limited to the use of a prefix. Rather, any suitable “address set” can be substituted for “prefix,” “sub-prefix,” etc. to describe how an address of interest (i.e., destination) can be categorized. The addresses need not be contiguous in a prefix boundary and can be as small as a single active address (i.e., “/24”). Active probes are sent to obtain candidate path measurements to network points up to, and sometimes including the destination, or to one node removed from any network point that cannot be probed due to disabling measures such as firewalls or filters. 
     Some of the embodiments of the present invention significantly reduce the number of active probes so as to not inhibit the efficiency of data routing by increasing the amount of traffic between the destination and the source. Some embodiments of the present invention can also provide a system and a method using a data structure that can store information, such as IP addresses, for announcing route changes and updates to a particular data path. The stored data within the data structure then can be modified in response to changes over time that occurs in a network or data route. 
       FIGS. 1A ,  1 B, and  1 C illustrate basic hardware components suitable for practicing a specific embodiment of the present invention.  FIG. 1A  is an illustration of an exemplary computer system  1  including display  3  having display screen  5 . Cabinet  7  houses standard computer components such as a disk drive, CD-ROM drive, display adapter, network card, random access memory (RAM), central processing unit (CPU), and other components, subsystems and devices. User input devices such as mouse  11  having buttons  13 , and keyboard  9  are shown. Other user input devices such as a trackball, touch-screen, digitizing tablet, voice or visual recognition, etc. can be used. In general, the computer system is illustrative of but one type of computer system, such as a desktop computer, suitable for use with the present invention. Computers can be configured with many different hardware components and can be made in many dimensions and styles (e.g., laptop, palmtop, pentop, server, workstation, mainframe). Any hardware platform suitable for performing the processing described herein is suitable for use with the present invention. 
       FIG. 1B  illustrates subsystems that might typically be found in a computer such as computer  1 . In  FIG. 1B , subsystems within box  20  are directly interfaced to internal bus  22 . Such subsystems typically are contained within the computer system such as within cabinet  7  of  FIG. 1A . Subsystems include input/output (I/O) controller  24 , System Memory (or random access memory “RAM”)  26 , central processing unit CPU  28 , Display Adapter  30 , Serial Port  40 , Fixed Disk  42 , Network Interface Adapter  44  (e.g., Network Interface Card, or NIC), which in turn is configured to communicate with a network, such as by electrical, radio, or optical means known in the art. The use of bus  22  allows each of the subsystems to transfer data among subsystems and, most importantly, with the CPU, where the CPU might be a Sparc™, an Intel CPU, a PowerPC™, or the equivalent. External devices can communicate with the CPU or other subsystems via bus  22  by interfacing with a subsystem on the bus. Thus, Monitor  46  connects with Display Adapter  30 , a relative pointing device (e.g. a mouse) connects through a port, such as Serial Port  40 . Some devices such as Keyboard  50  can communicate with the CPU by direct means without using the main data bus as, for example, via an interrupt controller and associated registers. 
     As with the external physical configuration shown in  FIG. 1A , many subsystem configurations are possible.  FIG. 1B  is illustrative of but one suitable configuration. Subsystems, components or devices other than those shown in  FIG. 1B  can be added. A suitable computer system also can be achieved using fewer than all of the sub-systems shown in  FIG. 1B . For example, a standalone computer need not be coupled to a network so Network Interface  44  would not be required. Other subsystems such as a CD-ROM drive, graphics accelerator, etc. can be included in the configuration without affecting the performance of the system of the present invention. 
       FIG. 1C  is a generalized diagram of a typical network that might be used to practice an embodiment of the present invention. In  FIG. 1C , network system  80  includes several local networks coupled to computer data network  82 , such as the Internet, WAN (Wide Area Network), or similar networks. Network systems as described herein refer to one or more local networks and network service providers that make up one or more paths from a source to a destination and vice versa. Network systems, however, should be understood to also denote data networks that include one or more computing devices in communication using any networking technology. Although specific network protocols, physical layers, topologies, and other network properties are presented herein, the present invention is suitable for use with any multi-path network relying upon more than one Internet/network service provider (e.g., a multi-homed network interconnected to other networks), especially those networks that employ Internet Protocol (IP) for routing data, such as flows having one or more packets of information according to the protocol. Furthermore, although a specific implementation is not shown in  FIG. 1C , one having ordinary skill in the art should appreciate that a data flow control system according to the present invention can be deployed within one or more data networks  82  or configured to operate with network system  80 . 
     In  FIG. 1C , computer USER 1  is connected to Server 1 , wherein the connection can be by any network protocol, such as Ethernet, Asynchronous Transfer Mode, IEEE standard 1553 bus, modem connection, Universal Serial Bus, etc. The communication link need not be a wire but can be infrared, radio wave transmission, etc. As depicted, Server 1  is coupled to the data network  82 , such as the Internet or, for example, any other data network that uses protocols such as Transmission Control Protocol/Internet Protocol for data communication. The data network is shown symbolically as a collection of server routers  82 . 
     The exemplary use of the Internet or another data network for distribution or communication of information is not strictly necessary to practice the present invention but rather is merely used to illustrate a specific embodiment. Further, the use of server computers and the designation of server and client machines are not crucial to an implementation of the present invention. USER 1  Computer can be connected directly to the Internet. Server 1 &#39;s connection to the Internet is typically by a relatively high bandwidth transmission medium such as a T1 line, a T3 line, Metro Area Ethernet, or the like, although it might be connected in a similar fashion as with USERL. Similarly, other computers  84  are shown utilizing a local network (e.g., Local Area Network, or LAN) at a different location from USERI Computer. The computers at  84  are coupled via Server 2  to the Internet. Although computers  84  are shown to include only a single server (e.g., Server 2 ), two or more servers can be connected to the local network associated with computers  84 . The USER 3  and Server 3  configuration represent yet a third network of computing devices. 
       FIG. 1D , as discussed earlier, shows the effects of typical multi-path (e.g., ECMP) techniques on a route control system using active calibration alone. Two possible paths exist between Washington D.C. and San Jose, Calif. for a given network service provider. The first path  170  traverses New York, Chicago and Seattle. The second path  171  traverses Atlanta, Dallas and Los Angeles. Suppose that the cost of using either of the paths is equal in the routing protocol. Most router vendors, when presented with two equal costs paths, load share the traffic between them making sure that paths in the same flow will follow the same path. The path selection process is typically vendor-specific and generally relies on known source and destination IP addresses as well as other metrics such as vectors, available bandwidth, transmission latencies, and distance. 
     Distance in a router and/or networking context can refer to metrics other than physical distance, such as bandwidth or time latencies between routers thus characterizing hops. Unless the source IP address and destination IP address are the same, the traffic may take a different equal-cost path. The implications for path calibration are that the active probes sent across the network between Washington D.C. and San Jose may take the northern path through Chicago  172  while the customer&#39;s traffic may take the southern path through Dallas  173 , because while the destination IP address is the same, the source IP address is different. Thus, the path measured may not be the path that is actually taken by the customer&#39;s traffic. The present invention, among other things, intelligently controlled routes containing data traffic using a system and a technique to assure service levels of customer data traffic in accordance with the present invention. 
       FIG. 1E  illustrates an exemplary data network within a portion of a network system  80  of  FIG. 1C  including NSPs  92 , and a flow control system in accordance with a specific embodiment of the present invention. Exemplary flow control system  90  is configured to communicate with one or more network elements of the data network. Although flow control system  90  is shown external of and in communication with the elements of source network  94 , switch  96 , and router  99 , flow control system  90  can be wholly embodied in any of the elements shown, or alternatively, can be distributed, in portions, over each of the elements. In another embodiment, flow control system  90  resides on one or more servers or network elements within exemplary source network  94 . 
     An exemplary data network includes one or more source networks  94 . A source network  94  typically is a local network including one or more servers owned and operated by application service providers, managed service providers, content delivery networks, web hosting companies, individual enterprises, corporations, entities and the like. Such service providers typically communicate information to users that are further removed from the multi-homed network service providers  92 , such as NSP  1 , NSP  2 , NSP  3 , . . . and NSPn. In one example, network service providers  92  are coupled to a source network or source node, point, or address so as to be considered a first set of data networks. These NSPs, or first set of data networks, are in turn coupled to a second set of networks, wherein the second set is connected to multiple other networks, thus establishing one or more paths from a source to a destination and vice versa. 
     The multiple connections between router  98  and multiple network service providers  92  provide an operator of source network  94  with information to direct data traffic according to the best performing network service provider. Switch  96  operates to transfer bidirectional data  99 , such as IP data, bi-directionally from source network  94  to router  98 . Although a single router and switch is shown, one having ordinary skill in the art will appreciate that either additional routers and switches or other suitable devices can be substituted according to another embodiment of the present invention. Moreover, switch  96  need not be used to practice the subject invention. In a specific embodiment, router  98  includes one or more routers running an exemplary protocol, such as TCP/IP, UDP, or BGP (e.g., BGP4, used between autonomous systems implementing networking equipment manufactured by companies such as CisCO™ or Juniper™ implementations), for example, and preferably has route visibility across multiple network service providers (“NSPs”). 
     In an embodiment of flow control system  90 , system  90  operates to measure end-to-end (i.e., source to destination and destination to source) data traffic  95  in terms of flow characteristics, such as performance, cost, bandwidth, and the like. Flow control system  90  also generates statistics associated with data paths across multiple network service providers in real time, or near-real time. Such statistics are communicated to source network  94  for providing network engineering personnel, for example, with report information  91  such that on-the-fly reports are created to provide information related to route-change activity, traffic performance as delivered to selected destinations and transit provider usage (i.e., bandwidth), cost, and the like. 
     In one embodiment of the present invention, a local computing device uses report information  91  from system  90  to generate visual representations on, for example, a graphical user-friendly interface (“GUI”) where the representations are indicative of data traffic along one or more paths (e.g., paths between a source and a destination). Network or systems administration personnel, or any entity responsible with flow control, with access to source network  94  can provide control information  93  (including, for example, flow characteristics) to flow control system  90  to modify system operation by, for example, changing data traffic flow from an under-performing current, or default, path to a better performing path. Intervention by network administration personnel, however, is not necessary for flow control system  90  to operate in accordance with the present invention. 
     Flow control system  90  further functions to compare specific data traffic flows (i.e., both uni- and bi-directional traffic flows outbound from and inbound into the data network) to determine whether a particular traffic flow meets one or more rules of an associated flow policy. A flow policy, as referred to herein, includes a set of one or more rules that is associated with a particular data traffic flow related to particular system user (e.g., as denoted by IP address prefix). 
     Minimum criteria can represent the lower levels of a range of values that defines acceptable routing behavior associated with a particular traffic flow characteristic. For example, a rule can set: the maximum acceptable cost, with or without regard to network service provider cost; the maximum load or bandwidth usage associated with traffic flows through specific providers; a range of acceptable (or non-acceptable) service providers; the maximum acceptable latency or loss over one or more paths across multiple network service providers; acceptable ranges of performance for each network service provider, such as maximum burst limits, minimum performance commitments and range of costs (i.e., cost structures with regards to time of day, type of traffic, etc.); and any other data flow characteristic that can influence the measurement or the control of data traffic. 
     Flow control system  90  further operates to detect when one or more rules, or flow policies, are violated and then to take remedial action. That is, flow control system  90  enforces policies associated with data traffic flow by correcting detrimental deviations in performance (i.e., service level assurance), costs or bandwidth (i.e., load in terms of percent capacity available per path). Flow control system  90  makes such corrections based on real- or near-real time traffic analysis, local path diversity (i.e., modifying one or more egress paths from a data network), and visibility (as determined, for example, by active probing) into downstream available paths. For example, for a destination related to a specific traffic flow, flow control system  90  directs, or re-directs, traffic to one or more alternative paths to resolve a particular flow&#39;s deviation in terms of flow characteristics, from its flow policy. 
       FIG. 2  illustrates a specific embodiment of flow control system  90  of  FIG. 1D . In another embodiment, flow control system in  FIG. 2  is a reactive flow control system. That is, a reactive flow control system is designed to react to policy violations indicating sub-standard routing of data traffic over one or more data networks or service providers (i.e., addresses pass-fail criteria) rather than optimizing performance at some targeted level of acceptable operation. In yet another embodiment, flow control system of  FIG. 2 , as described below, operates to optimize performance and/or usage by selecting the path having the most desired specific performance characteristic, for example, that at least meet the minimum level of service. 
     Flow control system  200  can include controller  205 , passive calibrator  203 , active calibrator  208 , configuration element  211 , and usage collector  214 , each of which can be realized in hardware, software, or a combination thereof. For example, controller  205 , passive calibrator  203 , active calibrator  208 , configuration element  211 , and usage collector  214  are software modules designed to perform specific processes, as described herein, in accordance to the present invention. Such modules can reside in one or more computing devices, such as the computing devices shown in  FIG. 1A , or alternatively, over one or more user-type machines (i.e., servers) coupled over a data network or network system. 
     Exemplary passive calibrator  203 , active calibrator  208  and usage collector  214  are coupled to controller  205  to, in part, provide flow characteristics of data traffic. Controller  205  receives monitored flow characteristics as well as flow policies to be enforced. User or machine-generated rules pertaining to the flow policies  206  for route control are provided to controller  205 . Specific parameters or operating guidelines for the present invention can be entered at controller  205  to ensure flow control system  200  maintains an appropriate level of operation, monitoring, and alarm status. Controller  205  is configured to determine if a flow policy is violated, and upon detection of such a violation, then to select a remedial action to resolve the violation. Configuration element  211  is coupled to controller  205  to receive information to initiate remedial actions and is configured to communicate such actions to data director  220 . Thereafter, data director  220  implements the corrective action to resolve the pending violation, for example, by changing the traffic flow from the current path to a better performing path. 
     Additionally, flow control system  200  can include traffic repository  221  and flow policy repository  218 . Exemplary traffic repository  221  and flow policy repository  218  are databases, such as a storage device, configured to store a large number of records in one or more data structures. Traffic repository  221  is designed to store and to communicate information related to traffic flow and route characteristics, and flow policy repository  218  is designed to store and to communicate policy information or rules to govern the performance and cost of each of the data traffic flows. One having ordinary skill in the art of database management should appreciate that many database techniques may be employed to effectuate the repositories of the present invention. 
     In operation, flow control system  200  of  FIG. 2  monitors egress and ingress data flow  201 , such as IP data traffic, to determine whether data flow  201  to and from source network is within the performance tolerances set by the associated flow policy. Flow control system  200 , in one embodiment, receives data flow  201  by replication, such as by a network switch, by using a splitter, such as an optical splitter, or any other tapping means know to those having ordinary skill in the art. Data flow  202 , which is exactly, or near exactly, the same as the information contained within data flow  201 , is provided to passive calibrator  203 . 
     Passive calibrator  203  monitors the data traffic of data flow  201  and communicates information  204  related to the traffic and traffic performance to controller  205 . Controller  205  is configured to receive policy data  206  representing one or more policies that correspond to a particular traffic flow, such as a particular data flow. Moreover, the particular data flow can be associated with a certain user identified by a destination prefix, for example. By using policy data  206 , controller  205  determines the levels of performance, cost, and/or utilization that the particular traffic is to meet. For example, controller  205  determines whether a particular traffic flow of data flow  201  is meeting defined performance levels (i.e., service levels) as defined by one or more requirements or criteria, such as inbound and outbound network latency, packet loss, network jitter, and the like. 
     Active calibrator  208  functions to send and to receive one or more active probes  207 , of varying types, into and from the data networks. These probes are designed to measure network performance including, but not limited to, the path taken across one or more available providers (i.e., to determine if a provider is a transit AS rather than peer AS), next hop-in-use, and other network parameters. To activate active calibrator  208 , controller  205  sends an active probe request  209  to active calibrator  208 . Such a request is required if controller  205  determines that additional information regarding alternative paths or network system characteristics are necessary to better enforce policies in reactive flow control systems, or alternatively, to prevent such policy violations in optimized flow control systems. 
     Usage collector  214  is configured to receive NSP data  217  representing one or more network provider configurations. Generally, such configurations include the number of paths (“pipes”) associated with each provider and the size thereof. Additionally, NSP data  217  can relate to a provider&#39;s cost or billing structure and can also include each provider&#39;s associated set or subset of addresses, each provider&#39;s billing methods (i.e., byte/min, etc.), etc. Moreover, usage collector  214  is configured to collect usage information  213  from the network elements, such as switches, border routers, provider gear, and other devices used to transport data over data networks. Usage collector  214  is configured to provide controller  205  with provider utilization and billing information  215 , which represents aggregated data based upon NSP data  217  and usage information  213 . Usage data or utilization data (not limited to those embodiments described herein) can be measured in various ways to include connection or link time, data packet volume, and/or other metrics not included here specifically. Other utilization and billing information  215  includes data that represents cost, billing, utilization, etc., for each network service provider of interest. 
     One having ordinary skill in the art should appreciate that NSP data  217  can be provided to usage collector  214  in a variety of ways. For example, data describing, defining, controlling, or modifying data paths as used for the data flows described herein can be provided by an entity having authority to do so, such as a network engineer entering the data into a computing device using a GUI in source network  94  of  FIG. 1E , which for example, can represent information displayed in  FIG. 27 . 
     Moreover, usage collector  214  is configured to monitor usage characteristics defining a network service provider&#39;s data traffic capacity, costs, etc. Usage data  213  provided to usage collector  214  includes usage information and characteristics from network elements, such as switches, border routers, routers, provider gear, and other devices used to transport data over data networks. Usage refers to the data (i.e., data such as X Mb samples at time ( 0 )) that represents instantaneous or near instantaneous measurement of characteristics (i.e., usage characteristics, data volume, etc.) that define, for example, the load and available capacity of each network service provider. Utilization is the usage rate over time. For example, suppose the usage collector monitoring NSP 1  measures the system&#39;s utilization of NSP  1 , or capacity over time, as X Mb at time( 0 ) and Y Mb at time( 1 ). This raw data, or usage, is used to calculate utilization, or usage rate for NSPI (e.g., Y−X/time( 1 )−time( 0 )). Bandwidth is the total capacity for each path or hop available for traffic flow. In one embodiment, the usage can be measured in any hop in any path at any number of hops or networks from a first point. Load is typically defined as the amount of capacity a particular path is used to carry data traffic and can be expressed as load/bandwidth. 
     Usage collector  214  is designed to generate utilization and billing information  215  based upon usage information  1213  and NSP data  217 . Since each of the providers has different cost and billing structures, as well as methods of determining usage costs, usage collector  214  operates to aggregate usage information  213  accordingly to provide controller  205  with utilization and billing information  215 . Software applications or other means (e.g., by human manipulation) may be used to implement utilization and billing information for financial accounting purposes. 
     Usage collector  214  then provides the utilization billing information  215  to controller  205  for each network service provider of interest. One having ordinary skill in the art should appreciate that the usage collector can provide additional information based upon the provider usage information, to the controller, as needed to better effectuate route control. 
     Controller  205  collects information (e.g., aggregated performance and usage characteristics) from each of passive calibrator  203 , active calibrator  208 , usage collector  214 , and optionally traffic repository  221 . Based upon the information collected, controller  205  determines a course of action that best alleviates the policy violations in respect to the information represented by policy data  206  that is conveyed to controller  205 . Once the course of action is determined, controller  205  initiates and sends a network routing change request  212  to configuration element  211 . In a specific embodiment, controller  205  also provides data representing one or more alternate data paths that can be used to resolve a policy violation. 
     Configuration element  211  is designed to communicate routing changes in the network to data director  220 . Once configuration element  211  sends one or more routing changes, data director  220  then moves the subject data flow  201  from a current path to another path (e.g., from NSPI to NSP 2  to NSPn or a first path of NSPI to a second path of NSPI). Data director  220  thus operates to distribute traffic to these destinations across multiple network service provider links based on, for example, the cost and performance measured across each link. 
     In operation, configuration element  211  communicates one or more routing changes  210  with data director  220 , for example, by using a routing protocol such as BGP. Configuration element  211  functions to dynamically control routing behavior by modifying the source address, for example, of the traffic passing through configuration element  211 . The source address is modified in a way that improves application performance as well as cost requirements. 
     The following discussion is a more detailed description of each of the elements of an exemplary control system  200 . Referring back to active calibrator  208 , active calibrator  208  provides active mechanisms within system  200  for determining the nature of downstream or upstream paths. This information is typically not available in any conventional protocol used on data networks such as the Internet, and is collected external to the normal processes of networking. As shown in  FIG. 2 , active calibrator  208  is coupled to controller  205  to provide at least a destination prefix that is not meeting the policy requirements, such as minimum performance level. Once received, active calibrator  208  then initiates a calibration process that determines some, most, or all of the available network paths to the destination address as well as performance levels. Controller  205  is designed to select the most suitable probes that active calibrator  208  is to use, based on the particular policy requiring enforcement or correction, and thereafter to initiate active probing of network paths using active calibrator  208 . 
     In one embodiment, active calibration probes are communicated to available network or Internet paths via probe path  207 . The returning active calibration probes enter via probe path  207  into active calibrator  208 . Active calibrator then forwards probe information  209  to controller  205 , which contains or has access to performance information including alternate available paths. Controller  205  then determines how best to enforce the specifics of the policy associated with the subject traffic flow. Exemplary active calibrator  208  employs active calibration mechanisms to provide, for example, long term statistics describing flow characteristics. 
     In another embodiment of the present invention, active calibrator  208  resides in data director  220  within, or alternatively, can be integrated into controller  205 . There are several proprietary implementations of commercially available routers suitable to practice the present invention. One example of suitable active probes is the RMON probe. Cisco systems use Service Assurance Agent (“SAA”) that is derived from the remote monitoring (“RMON”) probes to send out active probes. SAA allows routers to measure and report network-originated application round trip times (“RTT”). Although not every probe mentioned below is available in SAA for network calibration, one skilled in the art would appreciate how each of the following might be implemented to practice one or more embodiments of the present invention. 
     An exemplary active calibrator  208  can use ICMP (Internet Control Message Protocol) echo request or other ping-type probes, lightweight TCP-based probes, Sting probes, “pathchar” probes, lightweight probes using User Datagram Protocol (“UDP”) packets with a predefined TTL (time to live), traceroute probes, or other active probes that are suitable for use by active calibrator  208  in accordance with the present invention. As used herein, “weight,” whether heavy or lightweight, is a local measure of whether a particular data route is preferred over another. A weight is given to a data route by a particular router using a route map and is intended for use only by that router. Thus, the lightweight probes referred to herein indicate that they are intended for a specific predetermined router, per a route map created in accordance with an embodiment of the present invention. 
     These probes are received by active calibrator  208  of  FIG. 2  and can be sent out by their source addresses. Such probes can be sourced and received on an exemplary stats computer system resident, for example, in the local premises, or as a stats process on a router. The active calibrator and its use of probes operate in accordance to probes described in a U.S. Patent Application, entitled “System and Method to Assure Network Service Levels with Intelligent Routing,” having U.S. patent application Ser. No. 09/833,219 and filed on Apr. 10, 2001, and is incorporated by reference for all purposes. 
     Exemplary passive calibrator  203  of  FIG. 2  is configured to receive, without interfering with, network communication data  201 , such as customer network or Internet traffic. Network communication data path  201  (i.e., including one or more IP data traffic flows), as monitored by passive calibrator  203 , includes the default or currently routed path of the data traffic that is provided to passive calibration element  203  from data director  220 . The currently routed path is, for example, the path (e.g., hop-by-hop) between routers that a packet would take, as determined by standard routing protocols, flow control policy, or other performances parameters. Passive calibrator  203  is coupled (i.e., electrically, optically, by radio waves, etc.) to controller  205  to provide information which indicates whether the specific IP data traffic is within the range of acceptable performance metrics, such as determined by a flow policy. Passive calibrator  203  operates to instantaneously monitor all traffic received via data flow  202  and is designed to overcome the complications of relying solely on active traffic analysis, such as EMCP, as shown with respect to  FIG. 1D . When the controller addresses policy violations, for example, passive calibrator  203  operates to overcome the complications of performing only active traffic analysis in the presence of multi-path (e.g., ECMP). 
     In another embodiment of the present invention, passive calibrator  203  examines the traffic stream in both directions (i.e., ingress and egress) and classifies each of the traffic streams into flows. The data traffic flows can be monitored within passive calibrator  203  according to the underlying protocol state (e.g., such as regarding TCP sessions) over time. As another example, passive calibrator  203  classifies the traffic flow according to round trip latency, percentage of packets lost, jitter or another data flow characteristic for each of the traffic paths. Such traffic flow information is used to characterize the “end-to-end” performance of the paths carrying the traffic flows, which includes flow rates, and is aggregated into a series of network prefixes. 
     As described above, passive calibrator  203  is coupled to store, fetch and update traffic and route information stored in traffic repository  221  (connection not shown). Exemplary traffic repository  221  is a database configured to store and to maintain data representing traffic and route information, which is useful to the end user employing a flow control system, such as system  200  of  FIG. 2 , as well as the operators of, for example, a network service provider. The data within traffic repository  221  includes long term statistics describe the flow characteristics of the data traffic. These statistics can be used for reporting, analysis purposes, and providing general feedback to a user of a flow control system according to the present invention. 
     Such feedback can consist, for example, of types of traffic being sent, source addresses, destination addresses, applications, traffic sent by ToS or DSCP (“DiffServ Code Point”) setting (which might be integrated into a differentiated billing system), volume of traffic, and the like. These statistics are fed into traffic repository  221  where, for example, a reporting engine or some other analysis application can access to the statistics. The information stored in traffic repository  221  includes data representing such traffic route characteristics arranged in any suitable data structure as would be appreciated by one skilled in the art. 
       FIG. 3  is a detailed functional block diagram showing exemplary elements of a passive calibrator  303  according to an embodiment of the present invention. Passive calibrator  303  includes, for example, passive flow analyzer  330 , export flow analyzer  331 , and content analyzer  332 . 
     In one embodiment, passive flow analyzer  330  performs passive analysis on the traffic to monitor current traffic flow characteristics so the controller can determine whether the monitored current traffic flow meets associated policy requirements. Export flow analyzer  331  performs passive analysis on exported flow records from a network device, such as from those devices (e.g., router) that advertise traffic type, source and destination addresses, and other information related to the traffic that it travels across service provider links. An example of such a network device is Cisco&#39;s NetFlow™ product. In another embodiment, passive flow analyzer  330  operates in accordance to the passive flow analyzer described in the above-mentioned U.S. patent application of Ser. No. 09/833,219. 
     Content Flow Analyzer  332  performs passive analysis of specific elements of data content, such as web site content. Export flow analyzer  331  and content flow analyzer  332  determine a set of relevant prefixes or a prefix list  334  that is associated with a specific user&#39;s policy. Prefix list  334  is sent as data representing such prefixes to an active detection process in the controller. Prefix list  334  can be one or more lists or data structures configured to store data representing performance and usage characteristics and are designed to be receive a query, for example, by the controller. Once queried, the passive flow analyzer provides the one or more prefix lists, or portions thereof, to the controller for use in determining a policy violation, for determining which routes or path comply with the flow policy, which path is the optimum path for routing data, and the like. An exemplary prefix list that can be generated by export flow analyzer  331  and content flow analyzer  332 , as well as passive flow analyzer  330 . 
       FIG. 17  shows an exemplary data structure  1900  suitable for providing for one or more of the prefix lists described herein. Data structure, or list,  1900  includes many IP addresses  1920  with many records  1910  associated with each address (e.g., destination) or prefix of variable granularity. Each record  1910  includes an address  1920  (or prefix), a number of occurrences during a time period  1930 , number of bytes sampled  1940 , time interval in which sampling occurred (delta t)  1950 , new prefix flag  1960  (1 represents new prefix, 0 represents old prefix), or the like. 
     List  1970  includes aggregate flow information for each address  1920  and/or prefix. For example, record  1975  include the following data: for address 1.2.4.7, this address was monitored four times during the sampling time interval (delta)t with a total flow volume of 360 bytes. With record  1990  having a new prefix flag set (i.e., first time this address has been monitored), new prefix list  1980  includes address 1.2.4.9 having one occurrence (first time) over (delta)t interval. One having ordinary skill in the art should appreciate that other relevant data may be monitored and can be stored in list  1900 . Moreover, the data representing address, occurrence, number of bytes, time interval, etc., can be used to manipulate the data such in a way that the controller can easily obtain. 
     For example, the data stored within a list  1920  can be aggregated according to address or prefix. As shown in  FIG. 17 , aggregate list  1995  includes the group of addresses corresponding to 1.2.4.X. For example, the record  1997  of aggregate addresses contains data indicating that the aggregation of addresses had been monitored five times during the time interval and had a total volume of 540 bytes. One having ordinary skill in the art should appreciate that addresses or prefixes can be grouped or aggregated in many ways. 
     Export flow analyzer  331  and content flow analyzer  332  also are configured to notify controller  305  when a previously unseen prefix has been added to the prefix list  334 . New prefix notification signal  335  enables the control element  1005  to establish a new baseline performance for this prefix and to seed the routing table with a non-default path, or alternative path (which can be non-BGP), if necessary. In one embodiment, export flow analyzer  331  and content flow analyzer  332  provide for monitoring of performance characteristics. 
     Content flow analyzer  332  is typically used when the main source of traffic flow  340  is web site or other content. Content source  341  can be configured such that special or premium content  342  that must be optimized can be identified by the flow control system by using, for example, an embedded URL  343 . URL  343  redirects the client to a content server running on the content flow analyzer  332 . Content flow analyzer  332  receives a request for the content element, which is generally an image file (e.g., 1×1 GIF) and is invisible or imperceptible in relation with the main original content, and responds to the client with the content element  344 . Content flow analyzer  332  then stores or logs this transaction in log files and, by using the log files, content flow analyzer  332  is able to perform aggregation and assemble content prefix list  334 . The list  334  is passed along to controller  205 , for example, for active service level monitoring and policy enforcement. 
       FIG. 4  illustrates a functional block diagram of an exemplary content flow analyzer  432 . Content flow analyzer  432  handles requests  420  for a small element of content, which is, for example, a 1×1 pixel image file that is imperceptible (although it need not be) on the resulting page. The small element is associated with the premium or generally specific pages of a larger set of content. The small element is, for example, a small redirect URL embedded within the content. 
     The small redirect URL acts to generate an HTTP request  420  in response to the small element of content. Content flow analyzer  432  sees this request  420  and responds  422  to it with, for example, a lightweight HTTP server  453 . This server is fast and lightweight, and does nothing other than respond with the image file. The lightweight web server  453  logs the IP address of the client requesting the web page, and sends one or more IP addresses to aggregator  454 . Aggregator  454  aggregates individual IP elements  424  into prefixes of varying granularity (e.g., /8 through /32) and also aggregates the frequency that each prefix is seen over an interval of time. 
     That is, aggregator  454  classifies prefixes according to frequency of occurrence and provides aggregated (i.e., grouped) prefixes  426  to prefix list generator  455 . Prefix list generator  455  creates destination prefix list  428  according, for example, to a prefix&#39;s importance in relation to the overall operation of the system as defined by the aggregated or grouped prefixes  426 . For example, each monitored traffic flow is examined to determine the performance characteristics associated with a destination prefix or address. 
     Aggregate prefixes  426  can be generally classified in terms of flow frequency, and average or total flow volume. Prefix list generator  455  sends updates to current prefix list  428  to controller  205  of  FIG. 2 , and also notifies other elements of the system with new prefix notification signal  432  when a new prefix is observed. Prefix list generator  455  stores the prefix information  430  to persistent storage for reporting and analysis purposes. A new prefix provides an additional alternate path or path segment that was unknown until a certain point of time. The new alternate path or path portion associated with the new prefix can provide for flow policy compliance, and thus can be used to re-route or modify the routing of data in accordance with am embodiment of the present invention to correct a policy violation. 
     Referring back to  FIG. 3 , export flow analyzer  331  operates in conjunction with network elements that can export (i.e., communicate) flow information in a format useable by analyzer  331 . One exemplary format is the Cisco NetFlow™ export format. Any network element designed to export flow information, such as router  345  or a layer 2 switch, thus is also configured to passively monitor the traffic it is processing and forwards export records  346  to export flow analyzer  331 . Export flow analyzer  331  functions to process export flow records  346 , aggregates the flows into prefix elements, and generates prefix list  334 . The prefix list  334  is generally a subset of all prefixes observed by the flow control system. A prefix can be selected from prefixes in the prefix list  334  based upon flow volume and flow frequency over an observation period. The selected prefix is placed into prefix list  334  before the list passed along to controller  205  of  FIG. 2 , for example. 
       FIG. 5  illustrates a functional block diagram of exemplary export flow analyzer  531 . Export flow analyzer  531  includes format interpreter  549 , parser  550  and prefix list generator  552 . Format interpreter  549  is configured to receive export flow datagrams  520  from the network elements designed to send them. Format interpreter  549  then communicates individual flow information  522  to parser  550 . Parser  550  operates to interpret destination IP elements from the flows monitored by the passive calibrator. Parser  550  also aggregates traffic flow according to total flow volume or transportation rate (e.g., in bytes/time unit) as well as flow frequency of destination addresses, for example, into aggregate elements. Thereafter, parser  550  sends the aggregate elements  524  to aggregator  551 . Aggregator  551  then generates prefix-level destination information  526  (i.e., aggregate prefix volume and frequency) at a variety of prefix granularities (e.g., from /8 up through /32). In other words, aggregator  551  determines the frequency, session, etc. or for a specific prefix and the aggregate volume of occurrences related to that prefix over an observed time interval. 
     Destination prefix list  528  is generated by prefix list generator  552  by, for example, ranking and organizing traffic flow characteristics related to prefixes in order of relative importance. List  528  contains data representing an aggregation of prefixes and is organized by relevance, as determined by the system or an entity to ensure policy enforcement. For example, one or more prefixes can be ordered in terms of flow frequency and average or total flow volume in relation to prefixes available in the overall system. Prefix list generator  552  sends updates to the current prefix list to controller  205  of  FIG. 2  and also notifies other elements of the system when a new prefix is observed via a new prefix notification signal  532 . Prefix list generator  552  stores prefix information  530  to persistent storage for reporting and analysis purposes. 
       FIG. 6  illustrates a function block diagram of an exemplary passive flow analyzer  630  of  FIG. 3 . In one embodiment, passive flow analyzer  630  is designed to generate prefix list  634  and new prefix notification signal  635  and generates aggregated flow data  680 , including network performance and usage statistics (e.g., data) grouped into relevant characteristics. For example, prefixes of a certain size can be aggregated, or grouped, from highest traffic volume to lowest as observed over time. The aggregated flow data  680  is communicated to controller  605  and are used by the controller to determine whether the current traffic flow violates or fails to conform to an associated flow policy for a given destination. The passive flow analyzer  630  also functions to store aggregated flow data  680  in traffic repository  621 , where it can be used for characterizing historical route and traffic flow performance. In another embodiment of the present invention, a prefix list generator is not included in the passive flow analyzer of  FIG. 6 . 
     Passive flow analyzer  630  uses a copy of the traffic  602  via a passive network tap or spanned switch port, as shown in  FIG. 2 , to monitor the network performance for traffic. Passive flow analyzer  630  also can monitor and characterize UDP traffic patterns for detection of anomalous behavior, such as non-periodic traffic flow, or the like. Passive flow analyzer  630  can use various neural network techniques to learn and understand normal UDP behavior for the application in question, and indicate when that behavior has changed, possibly indicating a service level violation which can be verified or explained with well known active probing techniques. 
     Additionally, passive flow analyzer  630  is designed to be “application-aware” according to how each of the particular traffic flows is classified. Traffic can be classified according to the classifier described in the above-mentioned U.S. patent application Ser. No. 09/833,219. Passive flow analyzer  630  can inspect the payload of each packet of traffic  602  to interpret the performance and operation of specific network applications, such as capture and interpretation of the Realtime Transport Control Protocol (“RTCP”) for voice over IP (“VoIP”), for example. 
     In  FIG. 6 , passive flow analyzer  330  includes packet capture engine  650 , packet parser  651 , correlation engine  652 , and aggregator  653 . Packet capture engine  650  is a passive receiver configured to receive traffic (e.g., IP data traffic) coming into and out of the network. Control signals are exchanged between aggregator  653  and controller  605  (e.g., requests from controller  605 ). Capture of traffic is used to facilitate traffic analysis and for determining whether a current traffic route meets minimum service levels or policy requirements. Packet capture engine  650  is designed to remove one, several or all packets from a traffic stream, including packets leaving the network and entering the network. Packet capture engine  250  operates to remove certain packets up, for example, from the network drivers in the kernel to user space by writing custom network drivers to capture part of a packet. Using DMA, the partial packet can be copied directly into user space without using the computer CPU. Such packets are typically removed according to one or more filters before they are captured. Such filters and the use thereof are well known in the art and can be designed to, for example, remove all types of TCP traffic, a specific address range or ranges, or any combination of source or destination address, protocol, packet size, or data match, etc. Several common libraries exist to perform this function, the most common being “libpcap.” Libpcap is a system-independent interface for packet capture written at the Lawrence Berkeley National Laboratory. Berkeley Packet Filter is another example of such capture program. 
     Parser  651  is coupled to receive captured raw packets and operates to deconstruct the packets and retrieve specific information about the packet from each in the traffic flow. Exemplary parser  651  extracts information from the IP and TCP headers. Such extracted information from the IP headers include source and destination IP addresses, DSCP information encoded in the ToS (i.e., “type of service”) bits, and the like. DSCP carries information about IP packet QoS requirements. Each DSCP defines the Per Hop Behavior of a traffic class. DiffServ has 64 code points so that it can define 64 different types of traffic classifications. TCP header information includes source and destination port numbers, sequence number, ACK number, the TCP flags (SYN, ACK, FIN etc.), the window size, and the like. 
     TCP elements parsed from the TCP headers are especially useful in determining whether a policy is being enforced, in terms of performance. An increasing amount of traffic, however, does not rely on TCP and instead uses UDP. UDP does not contain the necessary information to determine service levels according to conventional approaches. 
     To determine service levels to these destinations, the present invention might employ a statistically relevant amount of collateral TCP traffic going to the same prefix or a series of active probes to the same destinations, and/or have the analyzer parse deeper into the packet and understand the traffic at the application layer (e.g., layer 7), for example. There are some protocols running on UDP that have very specific requirements, which are different from most other data traffic on the network. These protocols can be loosely classified as “real-time” protocols and include things like streaming media and Voice over IP. Packet loss and latency, below a certain level, can be secondary concerns for real-time protocols. 
     In some cases, however, reducing the variance in inter-packet arrival times (i.e., network jitter) might be desirable. Many real time protocols and standards such as H.323 as defined by the International Telecommunications Union (ITU) can report the jitter in back channel communication known as the RTCP (“Real-Time Transport Control Protocol”), which is used to distribute time-dependent media data via IP multicast with feedback. If passive flow analyzer  630  of  FIG. 3  is “application-aware,” it can capture and observe the contents of the RTCP and be aware when the underlying network path is not meeting minimum jitter requirements. This can trigger an SLA violation in the same manner that 30% packet loss would when monitoring packet loss. 
     Correlator  652  operates to interpret and to group the packet elements (e.g., TCP and IP) from the packets to determine the current service level of the flow and then groups the packets into a specific traffic flow. Flows are reconstructed, or grouped, by matching source and destination IP addresses and port numbers, similar to the process of stateful monitoring of firewalls. Correlator  652  determines the current service level by measuring several traffic characteristics during a TCP transaction. For example, correlator  652  determines the round trip time (“RTT”) incurred on a network, and hence, this serves as a measure of latency for the network traffic. 
       FIG. 7  shows how correlator  652  of passive flow analyzer  630  of  FIG. 6 , placed near a source (e.g., client having a source address), can determine the network latency (“NL”) and server response time (“SRT”) for a TCP traffic stream.  FIG. 8  shows how correlator  652  of passive flow analyzer  630  of  FIG. 6 , placed near a destination (e.g., server having a destination address), can determine the network latency (“NL”) and server response time (“SRT”) for a TCP traffic stream 
     Correlator  652  of  FIG. 6  determines NL, for example, by estimating the difference  791  of  FIG. 7  in time between a TCP SYN packet and its corresponding TCP SYN ACK packet. The difference in time between SYN and SYN ACK  791  is a rough estimation of the RTT excluding the small amount of time  790  that the server takes to respond to SYN. The SYN ACK packet is handled in the kernel of most operating systems and is generally assumed to be near zero. For each new TCP stream that is initiated from the source, correlator  652  can observe a time instantaneous value for network latency. 
     Packet loss is calculated, as a percentage, by correlator  652  by maintaining the state of all of the retransmitted packets that occur. From this value, correlator  652  calculates percentage packet loss from a total count of segments sent. 
     Correlator  652  also determines SRT  792  of  FIG. 7 , for example, by estimating the delta time (i.e., difference)  793  between, for example, the HTTP GET message  795  and the first data segment received and then by subtracting the previous value for the RTT. This assumes that the previous value for the RTT has not changed beyond an operable range since the TCP handshake occurred. The measurement shown by  794  indicates that measured congestion increases in the path as SRT  792  correspondingly increases. For purposes of this example, it is assumed that the data segments in the initial HTTP GET are sent back to back. In  FIG. 7 , the passive flow analyzer  630  is deployed close to (i.e., minimal or negligible latency due to geographically different locations) the clients requesting content from the IP data network, such as the Internet. 
     Correlator  652  also determines SRT  892  of  FIG. 8 , for example, by estimating the delta time between the HTTP GET message  893  and the first data segment  894 . In  FIG. 8 , the passive flow analyzer  630  of  FIG. 6  is deployed on the server end as will occur for most content delivery installations. 
     Referring back to  FIG. 8 , SRT  892  determined by correlator  652  depends on its location along the path that the traffic traverses. If passive flow analyzer  630  of  FIG. 6  is on the client side, server response time  792  of  FIG. 7  can be estimated as the delta in time between the HTTP GET Request message and the first data segment returned minus the RTT observed before the GET Request as shown in  FIG. 7 . If passive flow analyzer  630  of  FIG. 6  is closer to the server side, the estimation is essentially the delta in time between the GET Request and the response as shown in  FIG. 8 . Congestion estimations are also possible by using the TCP Congestion Window (“cwnd”) and by identifying the delta in receive time between segments that were sent back to back by the server, where the TCP congestion window controls the number of packets a TCP flow may have in the network at any time. Correlator  652  is coupled to provide the above determined exemplary flow characteristics to aggregator  653 . 
     Referring back to  FIG. 6 , aggregator  653  primarily operates to group flows going to (or alternatively, coming from) each set of specific destinations together into one grouping. Aggregator  653  uses the service level statistic for each of the individual flows, received from Correlator  652 , to generate an aggregate of service level statistics for each grouping of flows that are to go to the same destinations in the data network, such as the Internet. Aggregator  653  is also coupled to traffic storage  621  to store such aggregated (i.e., grouped by address prefix) traffic flow characteristics. Traffic flow characteristics (or traffic profiles) are then used for future statistical manipulation and flow prediction. In a specific embodiment, storage  621  is the equivalent, or the same, as storage  221  of  FIG. 2 . 
     The granularity of the destinations is the same as the granularity of changes that can be made in the routing table. Nominally, flow control system of  FIG. 2  can install routes with prefixes of any length (i.e., 0/ to /32), though the general practice is not to do so. Aggregator  653 , therefore, can start aggregating flow statistics at the /32 level (i.e., class C networks) and continue all the way up to the /8 level (i.e., class A networks) into a data structure, such as a patricia or radix trie, or a parent-child data structure, or the like. In this way, it is possible to seek very quickly the necessary granularity of the routing change that needs to be made to ensure the service level is met. 
     Aggregation techniques employed by aggregator  653  are used. to maintain the system  200  of  FIG. 2  to acceptable performance service levels, such as determined by one or more flow policy requirements. Since network performance has been shown not to generally follow conventional statistical distribution, such as Gaussian or Poisson distribution, average calculations for service levels across all flows are not as reliable a measurement of a typical performance behavior during a time interval. If the service level agreement (SLA) or policy, however, states that the average service level must be maintained, then the outlying occurrences of poor performance will cause the average to be skewed, thus requiring corrective action to restore the minimum service levels being offered. A meaningful way to describe typical service levels being offered across data flows can be to use median values, rather than average values, in some embodiments of the present invention. A person having ordinary skill in the arts will appreciate that either technique is possible and will depend on the definition of the service level that must be maintained. 
       FIG. 9  illustrates how passive flow analyzer  930 , according to another embodiment of the present invention, is capable of packet capture and flow reconstruction across more than one network interface, each interface represented by a network interface card (“NIC”). In practice, many switch fabrics are constructed in a manner by tapping into a single point in the data stream or replicating a single port. The switch does not guarantee that passive flow analyzer  930  will see all of the traffic in both directions. Bi-directional traffic is required for optional flow reconstruction for passive analysis. In  FIG. 9 , the switch fabric shown can be passively tapped at tap points  921  at four places (as shown) and connected to passive flow analyzer  930  at four different network interface cards (NIC)  922 . Passive taps at tap points  921  can be mirrored switch ports, optical/electrical passive taps, or the like. Passive flow analyzer  930  can include either a single or combined aggregated flow reconstruction element  953  that can collect captured data from multiple network interfaces in order to perform flow reconstruction. 
       FIG. 10  illustrates yet another embodiment of the present invention where passive flow analyzer  630  of  FIG. 6  is distributed in nature.  FIG. 10  shows traffic flow  1020  bi-directionally traveling via several local traffic source points. Distributed local passive flow agents  1025  can be tapped passively at tap point  1024  into traffic flow  1020 . Passive flow agents  1025  are distributed such that each agent monitors and conveys individual flow characteristics. The traffic sources are distributed across a layer 3 infrastructure, for example, and are separated by one or more routers  1026 . This arrangement prevents the passive flow analyzer  930  of  FIG. 9  from collecting information across the same layer 2 switch fabric as in  FIG. 9 . Each of the passive flow agents  1025  performs local flow reconstruction and then exports flow data records  1027  over the network to a central passive flow analyzer  1028 , performs flow aggregation and service level analysis across all of the distributed passive flow agents  1025 . 
       FIG. 11  illustrates a more detailed functional block diagram depicting multiple passive flow agents  1125  separately distributed and a single central passive flow analyzer  1128 . Each passive flow agent  1125  includes packet capture  1150 , parser  1151  and correlator  1152  functions on each of the local traffic flows. Correlator  1152  exports flow records  1129  with substantial data reduction to central passive flow analyzer  1128 . Substantial data reduction reduces the amount of information forwarded to the central passive flow analyzer, which can be effectuated by using well-known encoding techniques. Central passive flow analyzer  1128  accepts flow export records  1129  from each passive flow agent  1125  and central aggregator  1153  performs prefix aggregation on each of the exported flows. Thus, the centrally aggregated flow information can be used to determine if a particular policy violation is occurring. 
       FIG. 12  illustrates a detailed block diagram of usage collector  214  of  FIG. 2 . Usage collector  1215  operates to collect usage information  1273  from network providers, such as byte counters (i.e., the amount of traffic transmitted to and received from network service providers). Usage collector  1215  uses this information to calculate network service provider utilization, load, etc., of data paths associated with the provider. 
     Usage collector  1215  also operates to reconstruct provider billing records. Usage collector  1215  accepts provider configuration information  1271  related to each network service provider (NSP) connection. This NSP configuration information  1271  details provider interfaces on the various routers  1272  (e.g., egress routers), provider next-hop IP addresses traceroute probes (to verify the current provider in use with trace probes), billing period start and end dates, circuit bandwidth for calculating the utilization and price per megabit/sec, minimum bandwidth commitment, burstable rates, provider sampling interval, provider billing algorithm, a utilization alarm threshold and the like. 
     In operation, exemplary raw collector  1274  sends a query  1290  (e.g., SNMP) to collect interface raw byte counters from routers  1272  on each of the provider circuits at a specified sampling interval. Provider circuits include paths, pipes (virtual and/or physical), T1, and the like. Raw Collector  1274  places the raw byte counters  1280  into persistent storage for later reporting and analysis. Raw collector  1274  sends the raw information to two other components: utilization monitor  1275  and bill reconstructor  1276 . 
     Utilization monitor  1275  calculates the ingress and egress circuit utilization for each provider using the raw byte counts and the NSP configuration information  1271 . In one example, NSP configuration information  1271  includes the bandwidth of the provider&#39;s circuits. Utilization information  264  includes data representing utilization trends for use with short range forecasting models (e.g., ARIMA, exponential smoothing, etc.) such that utilization monitor  1275  can determine whether bandwidth is trending up or down (i.e., increasing or decreasing in size) for a given service provider. 
     Bill reconstructor  1276  uses the billing information from NSP configuration data  1271  to reconstruct the current provider billable rate for the current billing period. Billing information includes information explaining the methods that specific providers use to calculate costs, such as a billing rate. Such methods of calculating bills for using a network provider are well known in the art. Bill reconstructor  1276  applies similar provider billing methods to the raw byte counters from raw collector  1274  to generate the bill and related billing rates, etc. The generated bills, which can be mapped into dollar amounts, are typically estimates since the sample times between the provider and usage collector  1215  generally do not match exactly. Bill reconstructor  1276  will send billing information  1261  to controller  1202  for use in peak avoidance and least cost routing. Peak avoidance can be defined as a method of avoiding using a path or path portion at a higher a billing rate, such as shown in  FIG. 15 . Least cost routing refers to a method of using or defaulting traffic to the least expensive provider. 
     Additionally the information can be sent to controller  1202  for use in the least cost fix method of selecting the cheapest if performance is of negligible or no consequence. That is, controller  1202  uses data from billing message  1261 , including billing rates, to determine an alternate path based in part on a path&#39;s free bandwidth (i.e., path does not incur additional cost to use), in accordance with the flow policy. 
     Referring back to  FIG. 2 , configuration element  211  is coupled to controller  205  and to data director  220 . Controller  205  provides the best path, as defined by a particular flow policy, to reach a destination prefix to configuration element  211 . Configuration element  211  operates to change the default routing behavior (i.e., current path) for the destination requiring corrective action. Configuration element  211  changes the routing behavior by, for example, sending a modified routing table of addresses to data director  220 . 
     Once data director  220  receives this information, data director  220  informs controller  205  that a route change has been implemented. Thereafter, controller  205  communicates signal  230  back to passive calibrator  202  to clear its state and to resume monitoring the destination. The destination is monitored to ensure that the updated path of the routing table, or path, meets minimum service levels (e.g., no violations of SLA, or no unacceptable deviations from agreed upon performance metrics as defined by the associated flow policy). 
     In one aspect, configuration element  211  resides in a route server. In another aspect, configuration element  211  resides in a router and is configured to modify a route map or table. In yet another aspect, configuration element  211  is adapted to provide configuration information, or routing table. In still yet another aspect, the path information is stored within the configuration element  211  according to whether it is related to inbound or outbound traffic. 
       FIG. 13  shows an example of yet another embodiment of the present invention, where configuration element  211  of  FIG. 2  resides in a network element, such as route server  1391 . Configuration element  1384  of  FIG. 13  operates similarly to other adaptations of configuration elements described herein. That is, configuration element  1384  modulates the current or default routes of data traffic and thus modifies the default routing behavior, for example, in a local deployment (e.g., Point of Presence, or “POP”). Route server  1391  (“RS”) receives a full set or subset of routing tables from the data networks of interest. 
     In one embodiment, the routing tables are received into route server  1391  by way of one or more default BGP4 feeds  1392  into BGP4 Engine  1382  from a full set or subset of the local transit providers. BGP4 Engine  1382  integrates, or merges, the routes into a single BGP4 routing table  1383  of best available routes. In another embodiment, route server  1391  maintains an iBGP session with all of the internal BGP capable routers rather than maintaining the BGP4 sessions as shown in  FIG. 13 . With a single iBGP session there is no need to configure all of the BGP sessions with the network service providers before making route changes. 
     Configuration element  1384  is designed to receive one or more BGP4 routing tables  1383  from BGP4 engine  1382  and can be adapted to receive one or more control signals and data resulting from the control processes of controller  1305 . In operations, configuration element  1384  receives, from controller  1305 , the necessary routing changes to be implemented in default routing table  1388 . Then, configuration element  1384  incorporates one or more changes in modified routing table  1389 . 
     Thus, configuration element  1384  operates to modify BGP4 routing table  1383  and to generate one or more modified BGP4 routing tables  1388 . Modified BGP4 routing table  1388  includes changed routing  1389 , advertisements of more specific routes, etc. New modified BGP4 routing table  1388  is then fed to all BGP clients in the network, which then is used to guide traffic to the destination. 
     For a given source address, the ingress point into a network is determined typically by the advertisements of routes made to downstream providers and a provider policy (set of rules that is set up by such providers). Eventually, the network service provider (e.g., “ISP”) that is hosting the destination will receive such advertisements. 
     Controller  205  of  FIG. 2  is designed to receive performance characteristics, such as latency, loss, jitter, etc., as monitored by the calibrator elements as well as usage characteristics, such as bandwidth, costs, etc., as monitored by the usage collector. Controller  205  is coupled to policy repository  218  to receive flow policies, which typically include service level agreement (“SLA”) performance metrics. These metrics, or requirements, are compared against the monitored performance and usage characteristics. If a particular policy is violated (i.e., one or more performance metrics are outside one or more expected ranges or values), controller  205  determines a subset of one or more alternate data paths that conform to the associated flow policy. In another example, controller  205  selects a best or optimized path as an alternate data path that best meets the performance requirements and usage requirements, as defined by the policy. 
     The active calibrator and the passive calibrator provide performance characteristics. Regarding the active calibrator, controller  205  initiates active calibration by request active probing. The active calibrator sends one or more calibration probes on probe path  207  out into the one or more data networks. The returning probes on probe path  207  provide information back to controller  205 , which contains the identities of available paths and performance information related thereto. 
     Regarding the passive calibrator, controller  205  is designed to receive real- or near-real time network performance characteristics (i.e., loss, latency, jitter, etc.) from passive calibrator  203  as monitor in traffic flows in which it has access. After, controller  205  provides a routing change, or update, to configuration element  211 , it also communicates a signal  230  to passive calibrator  203  when an updated route change is made to a specific destination. Signal  230  initiates the clearing of the state of passive calibrator  203  so that the calibrator resumes monitoring the specific destination to ensure that the updated route of the routing table, or path, is flow policy compliant. Clear state signal  338  of  FIG. 3  depicts the signal that comes from the controller to initiate the resetting of the passive flow analyzer&#39;s state. 
     In one example, controller  205  operates to interpret the aggregated flow data over an interval of time for each of the groupings of destination prefixes. And if a policy violation occurs, controller  205  determines which of the alternate paths is best suited for the prefix or traffic type associated with the current traffic flow. Controller  205  then sends the necessary routing changes to configuration element  211 . That is, controller  205  resolve policy violations relating to non-compliant network performance characteristics, in accordance with the associated flow policy. This process can be repeated until the policy violation is resolved. 
     In another example, controller  1202  of  FIG. 12  is designed to receive real or near-real time data representing network usage characteristics from usage collector  1215 , such as usage rate, billing rates, etc. Controller  1202  uses this information to resolve policy violations relating to non-compliant usages characteristics, in accordance with the associated flow policy. That is, prior to or during a route change, controller  1202  not only does the controller consider the performance of alternate paths, but also whether those alternate paths either avoid peak data traffic over a specific provider&#39;s path (i.e., adequate bandwidth related to time-of-day) or are the least cost paths in view of the flow policies. 
     To resolve usage-type policy violations, controller  1202  is configured to receive routing tables, for example, to determine which of the current traffic flows or routing of data on certain paths, or path portions thereof, are congested (i.e., loaded) with respect to a particular provider path or paths. Controller  1202  also is designed to receive data representing flow volumes for each of the alternate provider paths to determine which subset of flows of a set of traffic flows to or from a given destination prefix are in compliance with the associated flow policy in terms of traffic flow volume. 
     An exemplary controller of the present invention thus is designed to obtain information related to the performance and usage of data networks and the make corrective action to effectively and efficiently route data over paths or path portions that meet at least associated policy requirements. 
     The following discussion relates to flow policies and the application of such policies in resolving policy violations and in enforcing the policy requirements or metrics. Referring back to  FIG. 2 , controller  205  is coupled to policy repository  218  for receiving one or more policies. As described above, a policy is a set of rules or threshold values (i.e., maximums, minimums, and/or ranges of acceptable operations) that controller  205  uses these rules to compare against the actual flow characteristics of a specific traffic flow. For example, a policy can be the user-defined mechanism employed by controller  205  to detect specific traffic flows that are to be monitored and acted upon, if necessary. As an example, a policy can also specify how the particular policy should be enforced (i.e., in includes a hierarchical structure to resolve violations from highest to lowest precedence). Although an exemplary policy includes requirements, or rules, related to detection, performance, cost, and precedence, one having ordinary skill the art should appreciate that less, or additional parameters, can be measured and enforced according the present invention. 
     Detection is defined as the techniques or mechanisms by which flow control system  200  determines which traffic should be acted upon in response to a policy violation. The traffic flow can be identified, by name, by source or destination addresses, by source or destination ports, or any other known identification techniques. For example, a policy can be identified by address prefix. That is, system  200  will monitor the traffic flow to and/or from a specific prefix, and if necessary, can enforce the associated flow policy in accordance to its requirements. Further regarding detection, a policy defined for more specific prefixes can take precedence over more general prefixes. For example, a policy defined for a /24 prefix can take precedence over a /16 prefix even if the /16 prefix contains the specific /24. 
     Performance can be a policy requirement that describes one or more target performance levels (i.e., network/QoS policy parameters) or thresholds applied to a given prefix or prefix list. Although more than one performance-based policy requirement may be defined, in this example only a single policy is applied to a given prefix or prefix list. Exemplary performance requirements include loss, latency, jitter, and the like. 
     Moreover, such requirements can be configured either as, for example, an absolute, fixed value or as an Exponentially Weighted Moving Average (“EWMA”). Absolute value establishes a numerical threshold, such as expressed as a percentage or in time units over a configurable time window. The EWMA method establishes a moving threshold based on historic sampling that places an exponential weighting on the most recent samples, thereby asserting a threshold that can take into account current network conditions as they relate to historic conditions. 
     Cost is expressed in the policy definition in terms of precedence and whether the policy is predictive or reactive. Costs also can be characterized by usage collector  214  of  FIG. 2  through bill reconstruction and reconciliation of bandwidth utilization in both aggregate and very granular levels (e.g., by /24 destination network). Cost predictive requirements are used to proactively divert traffic from one provider to another in order to avoid establishing a peak (i.e., “peak avoidance”) that may trigger a new or higher billable rate. Cost reactive requirements are used to reactively divert traffic from one provider to another when a minimum commit rate or current billable rate is exceeded or when like cost requirements are not in compliance. 
     Typically, both cost predictive and reactive requirements result in a binary decision (i.e., a circuit or path, for example, is either in compliance with or in violation of a flow policy). In the case of predictive cost, the transit circuit is either in compliance, or soon to be violation of a flow policy. Regardless, an action must be taken to resolve the situation, unless cost is preceded by performance (i.e., performance requirements are to be addressed prior to making a cost-based change). 
     Precedence is a policy requirement that describes one or more target usage or utilization characteristics or levels. Precedence can include provider preference and maximum utilization (i.e., load) requirements. The provider preference requirement is, for example, an arbitrary ranking of providers that is used when an action must be taken, but when two or more transits may be selected in order to enforce the policy. The flow control system can automatically set the provider or path preference requirement if it is not configured explicitly by the system&#39;s operator. This requirement is then applied as a tiebreaker in deadlocked situations such that the provider with the highest preference wins the tie and thus receives the diverted traffic flow. 
     The maximum usage requirement can be used as either may also be used an actual operational threshold not to be exceeded or as a tiebreaker. Maximum usage is configured, for example, in the transit provider section of the configuration and takes either a percentage argument (i.e., in terms of available bandwidth), or alternatively, can be set as an absolute value in terms of Mb/s (i.e., not to exceed available bandwidth). 
     The following is an example of a policy used with a controller to determine whether the specific policy is in compliance, and if not, to determine the course of action. 
     For example, consider the following policy as used for a particular traffic flow: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 Policy Requirement 
                 Precedence 
                 Value or Threshold 
               
               
                   
                   
               
             
            
               
                   
                 Loss 
                 10 
                 2% 
               
               
                   
                 Latency 
                 20 
                 EWMA 
               
               
                   
                 Cost 
                 30 
                 Predictive 
               
               
                   
                 Maximum usage 
                 40 
               
               
                   
                 Provider Preference 
                 50 
               
               
                   
                   
               
            
           
         
       
     
     Suppose that the traffic flow is associated with a prefix of 24.0.34.0/24, is currently carrying traffic at 240 kbits/sec, and is reached via provider  1  of 3. Provider  1  is currently carrying 2 Mbits/sec and has a minimum commit of 5 Mbits/sec. 
     The controller of the flow control system using the policy can monitor the alternate traffic routes, or paths, and can determine the following flow characteristics as they relate to the providers: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Requirement 
                 Value for ISP1 
                 Value for ISP2 
                 Value for ISP3 
               
               
                   
               
             
            
               
                 Loss 
                 5% (violation) 
                 Not available 
                 Not available 
               
               
                 Latency 
                 140 ms 
                 Not available 
                 Not available 
               
               
                 Cost 
                 In compliance 
                 In violation 
                 In violation 
               
               
                 Max Usage/as 
                 5 Mb/s 
                 5 Mb/s 
                 5 Mb/s 
               
               
                 Measured 
                 2 Mb/s 
                 4 Mb/s 
                 5.5 Mb/s 
               
               
                 Latency 
                 (compliance) 
                 (compliance) 
                 (violation) 
               
               
                   
                 100 ms 
                 100 ms 
                 100 ms 
               
               
                   
               
            
           
         
       
     
     In this case, ISP 1  is in a violation state since loss of 5% exceeds the maximum loss requirement of 2% and since loss has been designated with the precedence of 10, with 50 being the lowest. Corrective action must be taken. The policy will be enforced without latency or loss information (i.e., because there is, for example, no visibility into the performance of the other links). In this case, the controller may initiate active probing using the active calibrator to determine whether the other ISPs (including ISP 2  and ISP 3 ) are in compliance. Alternatively, the controller might determine the course of action based on the next parameter in the policy where the requirement is known (e.g., cost in this case). Since ISP  2  is in compliance and ISP  3  is not, ISP  2  would be chosen by the controller. If the two were both in compliance, the controller would go to the next ranked requirement, which is MaxUtil. If this is the case, ISP 2  is still selected. 
     In summary, the policy, such as the above exemplary policy, is input into the controller  205  of  FIG. 2  and is associated with, for example, a specific prefix. The general detection method (absolute, baseline/historical, etc.) can be specified as per prefix, thus specifying hard or absolute thresholds for some destinations that are well known, while using a baseline method for other destinations. The policy also defines the resolution method (e.g. procedure) to be used in the combination with performance metrics that must be met before the violation is considered resolved. Other parameters such as cost and utilization thresholds can be set per prefix. This gives the controller an indication of which prefixes should not be moved for cost or utilization reasons and which prefixes should be moved under any circumstances. 
     In order for controller  205  to handle peering connections, controller  205  communicates with the data director  220  to retrieve reachability information (i.e., routing tables) for the specific prefix that is about to be changed. In the case of transit circuits, controller  205  uses active calibrator  207  to determine reachability information (i.e., routing tables) for a given destination by, for example, sending active probes to the destination and then waiting for the response. Although peering connections can often be unreachable, it is possible for active probes to succeed since some providers may not effectively filter traffic at a peering point and instead rely on an honor-like system to ensure that only traffic to those advertised destinations is received. 
       FIG. 14  illustrates how the availability of “free” bandwidth is expressed for a given provider and as measured by usage collector  214  of  FIG. 2 . Over any given time period from t 0  though t 1 , current usage rate  1602  and the current billable rate  1600  is determined. As shown, time point t 0 . 5   1603  represents an over-sampled time point. Difference  1601  between these two values represents an amount of bandwidth available to be used without incurring any additional cost (i.e., “free” bandwidth). The free bandwidth per provider can be used to select a subset of compliant providers when a performance-based policy is in violation by the current or default provider. Additionally, this information can be used to apply cost and/or load-based policies for each provider. 
       FIG. 15  depicts how usage collector  214  calculates the time-continuous billable rate as shown in  FIG. 14 . Most providers start out with a minimum commitment level  1710 . If the current usage starts out below that commitment, the free bandwidth  1711  is shown below level  1710 . Samples are collected at twice the provider sampling rate, for example, to ensure that an accurate rate is being calculated (i.e., this is a conservative estimate and if the rate deviates from the provider rate, it will be higher and represent an overestimation of the billable rate). The small tick marks on the time axis represent the samples collected by the system (i.e., over-sampling). When enough samples are collected, the billable rate, which generally can be expressed as the 95 th  percentile of most or all rate samples, may exceed the minimum commitment as shown by successively higher tiers  1713  of the billable rate in  FIG. 15 . When the traffic drops back down below this rate, a new billable rate  1714  is set and the system again has free bandwidth  1718  below level  1714  available for use. 
       FIG. 16  shows how an exemplary system  200  can detect a cost-based policy violation. Suppose the cost policy requirement is defined to be an absolute threshold, as shown by  1813 . This threshold can be an absolute rate or a set dollar amount to spend (which is converted by the system to an average billable rate). On a sample-by-sample basis, the actual traffic rate  1814  should be such that a new billable rate above  1813  is never established. Using short range forecasting techniques, the traffic rate for the next few samples  1815  can be forecasted, and if this forecast predicts that a new billable rate  1816  will be established, controller  205  of  FIG. 2  can react by moving traffic off of this provider. In some embodiments of the present invention, using data contained in a routing table enables data traffic flow to be altered between multiple providers in a multi-homed networking configuration. Using convergence point analysis, which is described below, some embodiments of the present invention can improve the efficiency of conventional data traffic flow techniques and technologies so as to maximize efficiency by reducing the amount of traffic, particularly where multi-homed networking configurations exist. 
     In accordance with one embodiment of the present invention, an exemplary method and system establishes a reference for monitoring the performance of candidate paths over which data flows between a source and a number of destinations within, for example, a particular address space. The paths are monitored to determine whether the associated flow characteristics, such as performance, cost, bandwidth, and the like, are suitable for routing data in accordance with a policy. As candidate path performance changes over time, such as degradations in performance, the method and system changes the routing of data. 
     To establish a reference, the topology of the network and its candidate paths are discovered by, for example, “path tracing.” That is, the network topology is identified by the structural and/or functional features of the candidate paths, including nodes on each of the paths. In one embodiment, one or more discovery probes “trace” the paths of available candidate routes. To trace the paths, discovery probes generate data for distinguishing the candidate paths by identifying the nodes on the paths and by comparing path performance (e.g., in terms of flow characteristics). This data can be gathered and stored in the exemplary data structures of  FIGS. 20C ,  21 A and  24 , as described below, for route control purposes. The results of path tracing can yield data representing characteristics (e.g., RTT, loss, etc.) from which candidate paths can be described. Statistical analysis of the data gathered from path tracing can be used to construct (i.e., model) and identify available candidate paths in which to route data over. One having ordinary skill the art should appreciate that other methods of discovering candidate paths are within the scope of the present invention. 
     In one embodiment of the present invention, a discovery probe is a path trace probe configured to determine at least the performance characteristics associated with a candidate path. Path trace probes can also be used to identify nodes (e.g., network elements or the like), address spaces (e.g., subnetworks), specific destinations (e.g., identified by a unique network identifier, such as a “/32” IP address), and other aspects of a network. Once discovered, the information obtained from path traced probes can be considered in the decision on how to select appropriate paths for optimal route control. 
     In another embodiment, an exemplary flow control system is configured to use passive flow analysis, as described above, to identify and characterize the performance of candidate paths. Hence, passive flow analysis and discovery probe path tracing can both be used to obtain data flow information, such as data path latency, round trip times (RTT) in data pathing, and other like characteristics. This information is useful in generating a topological model or map of candidate paths from which to guide data routing decisions. As will be shown, by leveraging topology information aggregated in routing tables or other data structures, for example, according to an exemplary method of the present invention, the volume of monitoring probe traffic can be reduced, which, among other things, minimizes triggering security measures unnecessarily. Moreover, appropriate lengths of advertisements can also be determined to route data according to an optimized aggregation of destinations (e.g., destinations described by subset of addresses). With optimized aggregation of destinations, computational overhead (computing power, memory, etc.) is reduced. 
     Once candidate paths are discovered and described, each candidate path is evaluated to identify a reference to monitor data flows. For example, the reference could be any common node that is associated with two or more paths. A common point or node where at least two candidate paths intersect, or converge, is referred herein as a “convergence point.” A property of most convergence points is that between a node designated as the convergence point and a destination each of the candidate paths share the same path. That is, the diversity in each of the candidate paths become non-existent (i.e., path diversity is zero). Since the nodes located between the convergence point and the destination are the same on non-diverse portions of the candidate paths, only the convergence point need be monitored (e.g., by active probing) to determine the flow characteristics along the candidate paths between a source and a destination. 
     In accordance with convergence point analysis methodologies of the present invention, convergence and sub-convergence points are identified and monitored to determine an efficient data route. Sub-convergence points are points that have less than the largest number of paths that converge into a non-diverse path portion. For example, node  1867  of  FIG. 18  is sub-convergence point since only two paths of interest converge at node  1867 , whereas three paths intersect at node  1875 . With three paths (i.e., the largest number of converging paths) converging at node  1875 , this node is denoted as the convergence point. 
     In one embodiment of the present invention, convergence points are used to monitor one or more addresses aggregated in a specific address space that can be identified by a destination prefix, which can be monitored by one monitoring probe, such as an active probe. In another embodiment of the present invention, a convergence point can be monitored for addresses associated with multiple destination prefixes. For example, a convergence point can be used to monitor a specific destination described by 10.0.1.124/32 as well as other destinations included in an address space identified as 10.0.1.0/22, which includes multiple subnetworks, one of which is 10.0.1.0/24. In some embodiments, multiple path traces to a convergence point over multiple paths can be employed to determine at what level of granularity is optimum at which to aggregate a set of addresses. The resulting aggregated set of addresses can also be referred to as an address space. An exemplary convergence point analysis methodology is further described below with regard to  FIGS. 21A and 24 , with particular use of convergence point and next hop information, respectively. Convergence point analysis is designed to at least reduce much of the overhead associated with sending numerous active probes to cover most or all of the destinations. 
     Once path trace probes discover candidate paths between a source and a destination, and the network topology is defined, convergence points can be established to provide a reference for monitoring path performance. By monitoring the reference as a probe point, the number of active measurements that encounter network security measures, such as filtered probes, are reduced. It should be noted that “a source” can refer to one or more entities that generally provide data flow. A source can also refer to a network element, such a router, for communicating data along the paths. Further, a source (such as Sources A, B, and C below) can also refer to egress routers associated with (and sometimes a hop within) a specific NSP. “A destination” can refer to a single destination (e.g., IP address) as well as an address space in which a subset number of destinations (i.e., subset of IP addresses) reside. The terms source and destination can be used interchangeably. 
     In some embodiments, convergence points can be used to provide a reference where nodes cannot be identified and/or are nonresponsive. Nonresponsive nodes hinders the development of a comprehensive understanding of the network topology. Without compensating for the loss of identifying nonresponsive, route control most likely will not be optimal. 
     Nonresponsive nodes are observed when a candidate path includes a data filter, a firewall, or any other security or traffic minimization mechanism. An example of a nonresponsive node is a node that filters traffic in accordance with a NSP&#39;s policy. By using convergence points as a reference probe point proximate (e.g., one node or hop from a nonresponsive node) to the nonresponsive node, paths downstream (i.e., between the convergence point and destination(s)) can be characterized for purposes of route control. 
     As will be described below in connection with  FIGS. 22 and 23 , for example, specific embodiments of the present invention provides for improved route control techniques over that of conventional route control techniques in that security features of destination networks are neither alarmed nor triggered in response to excessive active probing. 
     After candidate paths are discovered and convergence points identified, the convergence points are monitored to determine whether a path over which data is routed is compliant with at least one policy (i.e., flow characteristics are within acceptable service levels). Active probing of a convergence point application yields, for example, RTT, loss, latency, as well as other performance characteristics for the diverse portion (i.e., between the source and a convergence point) of the network path(s). Consequently, the result(s) from a single active probe can be reported for prefixes sharing a convergence point without actively probing nodes associated with each path related to a destination prefix. 
     Again, by actively probing convergence points where multiple paths intersect, the number of points that need to be actively probed is reduced. This is possible because the convergence points can represent an aggregation of many destinations, where one probe can characterize the path or paths associated with a destination related to the convergence point. Unlike path tracing, which can require diverse probing of numerous different points to discover available paths, active probing in accordance with an embodiment of the present invention monitors specific probe points to determine whether a path&#39;s performance has changed. Such changes can prompt a route change from the current path over which data is routed to another path that can alleviate at least the noncompliant performance characteristic associated with the current path. Such route changes can be implemented by an exemplary system described in connection with  FIGS. 2 ,  25 , etc. 
     In accordance with an exemplary convergence point analysis method of an embodiment of the present invention, active probes are generated by the active calibrator ( FIG. 2 ) and are directed to probe a specific convergence point. In other words, this reduces the need to generate large numbers of probes for relevant addresses associated with shorter advertisements (again, shorter advertisements of addresses and netmasks are indicative of larger amounts of addresses that require probing) that otherwise are subject to probing. In conventional systems, by contrast, a large volume of active probes are required to determine acceptable, alternate candidate routes. The corresponding large volume of active probing can themselves thereby degrade network performance by congesting routes. Additionally, increased amounts of probes may be unwittingly generated if a point fails to respond to active probing. As discussed above, path trace probing can determine which probed nodes are convergence points. When discovered, the active calibrator of an exemplary flow control system generates and sends an active probe to a convergence point. When determined, the convergence point is monitored for changes using active probing (i.e., by periodically sending an active probe to the specific convergence point). 
       FIG. 18  is representative of several data networks for which route control in accordance with an embodiment of the present invention can be employed. An exemplary network arrangement  1800  of five network service providers (NSPs)  1810 ,  1820 ,  1830 ,  1840 ,  1850  is shown along with three distinct data paths  1860 ,  1870 , and  1880 . The three candidate paths  1860 ,  1870 ,  1880  represent data paths traversing NSPs  1810 ,  1820 ,  1830 ,  1840 ,  1850  to transfer data between a source and a destination. Along each data path are numerous nodes or “points”  1861  which represent connective points in the transmission of data via one or more network. The portion of a path between two nodes can be a “hop,” but is not limited as such. A route can also be composed of several hops between a source and a destination node. 
     Again, convergence points, generally embodied as nodes on a network topology, are located at the intersection of two or more converging data routes. The use of convergence points, as described above, according with an embodiment of the present invention enables the determination of the most efficient data route or routes between a source and a destination along a network topology where multiple data paths are present. Convergence point analysis will be described in greater detail below in connection with  FIGS. 18 through 28  below. 
     In  FIG. 18 , three distinct data paths are illustrated. Data path  1860  extends from the source through NSP 1   1810 , NSP 4   1840 , and NSP 5   1850  to the destination. Data path  1870  extends from the source through NSP 2   1820 , NSP 4   1840 , and NSP 5   1850  to the destination. Data path  1880  extends from the source through NSP 3   1830  and NSP 5   1850  to the destination. A source data flow is communicated first through NSPs  1810 ,  1820 ,  1830 . Data then passes through NSPs  1840 ,  1850 . In a multi-homed situation, source data flows can enter a data path through multiple NSPs which, although not shown in  FIG. 18 , is not meant to be a limitation of the present invention. In  FIG. 18 , though, data path  1870  intersects with data path  1860  at convergence point  1867 . Path trace probes can be transmitted along data paths  1860 ,  1870 , and  1880  to discover any convergence point, such as  1867  or  1875 . Responsive probe data is received from path trace probing one or more points along data paths  1860 ,  1870 , and  1880  to construct available candidate paths. In particular, active probing of convergence points and responsive data is analyzed by active calibrator  208  and controller  205  to efficiently control data routing, as described above with regard to controller  205  of  FIG. 2 . Multi-homed organizations such as a business enterprise with widely-dispersed geographic resources using multiple network service providers can be associated with sources A, B, and C in  FIG. 18  from which to communicate data via the NSPs shown. 
     In other embodiments of the present invention, active probes can be sent to a node that is proximate to (e.g., one hop away from) the destination. In this embodiment, a destination (or intermediate node) may have failed to respond to active probing and answer packets, resulting from network administrative measures such as a firewall or filtering of packet data. 
     NSPs  1810 ,  1820 ,  1830 ,  1840 , and  1850  can represent distinct communication networks that provide and operate backbone components of various electronic data networks such as the Internet, Arpanet, etc. Examples of NSPs include AT&amp;T, Cable &amp; Wireless, Sprint, UUNet, Verizon, Deutsche Telekom, British Telecom, and others, but the invention is not intended to be limited to these companies. 
     In the example illustrated in  FIG. 18 , data paths  1860  and  1870  converge at convergence point  1867 . Moreover, the hop(s) and path portion between points  1867  and  1875 , which include node  1865 , has a network path diversity equivalent to zero because both paths no longer have diverse paths (i.e., both points share a hop). At a node in NSP 5   1850 , all three candidate paths converge at convergence point  1875 . Where the remaining path to the destination is common, performance experienced on this segment of the data path will be common for candidate paths. That is, the network path diversity for each data path  1860 ,  1870 , and  1880  is zero. 
       FIG. 19A  is an illustration of nodes associated with exemplary network  19 A 00  including candidate paths A and B. Although individual nodes are represented, such as A 1 , B 1 , B 2 , etc., one or more nodes can be included in a single AS, thus representing a single hop across that AS. Typically, however, a single hop can be represented between each node along paths A and B. Although represented in  FIG. 19A  for purposes of illustration and explanation, one of ordinary skill in the art would comprehend that the path portion between each of the nodes need not necessarily limit its representation to a hop. 
     Exemplary network  19 A 00  of  FIG. 19A  illustrates two sources (Source A and Source B) and a specific destination computing device  1952  having a specific IP address of 10.0.1.125/32. Computing device  1952  is associated with address space  1951 , which can be described as 10.0.1.0/24. Also shown are exemplary data structures  19 A 60 ,  19 A 70  and  19 A 80 , which can reside in repository  2511  of  FIG. 25  (but are not limited thereto), for relating data representing nodes characteristics, such as node identifiers. Although each node in  19 A 60  and  19 A 70  is represented as a number, such as “first, second, etc.,” the nodes can also be distinguished by their relative distance from the source, hop count, by TTL values over each path to reach a convergence point (e.g., convergence point  1 ), or any other known method of distinguishing such nodes. 
     Data structures  19 A 60 ,  19 A 70  and  19 A 80  illustrate but one possible way to determine which nodes on candidate paths are convergence points. Data structures  19 A 60  and  19 A 70  are designed to store data representing relationships in records  19 A 66  between each node  19 A 62  on a path and a node characteristic, such as a node identifier  19 A 64 . In a process similar to that in with respect to  2220  of  FIG. 22 , a path trace probe is sent to each node encountered along that path, with the results recorded. For example, along the Path A (e.g., from SA to node A 10 ), each node  19 A 62  such as the “ . . . fifth, sixth, seventh . . . ” nodes on Path A will be associated with an identifier  19 A 64 . In this case, identifiers “A 5 , A 6 , and A 7 ” are associated with the “ . . . fifth, sixth, seventh . . . ” nodes. Similarly, Path B (e.g., from SB to node B  14 ) is discovered and corresponding nodes identified. The results of discovery can be stored in data structure  19 A 70 . 
     Logic within an exemplary flow control system (not shown) is configured to compare each node to determine whether it has been identified, such as described in regard to  2230  of  FIG. 22 . Data structure  19 A 80  is used to record an instance when a node on one path is found to lie on another path. In this case, a common point between paths are recorded as an identified node  19 A 82 , such as “A 6 , B  10 ” in record  19 A 88 . If the flow control system determines that “A 6 , B 10 ” is a convergence point, it is so identified and recorded as “CPI” as a convergence ID  19 A 84  in record  19 A 88 . In this case, if the node identifier is an IP address, the IP address of CP I (i.e., A 6  and B  10 ) can be recorded in  19 A 86  as “66.185.23.1.” Also, data structure  19 A 80  shows that a convergence point CPI can be associated with one or more destinations  19 A 90  (e.g., destination network). Here, convergence point CPI is shown to be related to both destination networks 10.0.1.0/24 and 10.0.2.0/24 and thus can be a reference probe point for both. It is noteworthy that identifiers  19 A 64  can employ an IP address (rather than the alphanumeric label shown in this example) or any other known identification means. 
     After node  1910  is identified as a convergence point, this node can be actively probed periodically, or as deemed necessary, to determine whether a path to destination  1952  is performing in accordance with the relevant policy. In this example, no other convergence point has been discovered and the path portion from node  1910  to address space  1951  is determined to be non-diverse. And since computing device  1952  resides the address space defined as 10.0.1.0/24, then node  1910  is a suitable probe point to monitor traffic flows between address space  1951  and Sources A and B. Hence, an active probe sent to node  1910  can at least ascertain the performance of a path of interest. 
     Consider the following example, which illustrates when active probing of node  1910  is performed to monitor traffic flows between a source and a destination. In this case, assume that K 1  represents the RTT of 30 milliseconds (ms), K 2  represents the RTT of 20 ms and K 3  represents a RTT of 20 ms. Further, suppose the policy governing route control in this example has a margin or tolerance of 5 ms. That is, a current route&#39;s performance will not trigger corrective action until the performance degrades beyond 5 ms. In practice, such margins are configurable by a user. Note that K 3  is common to both Paths A and B and cannot be avoided (data communicated along both paths must traverse the corresponding path portion), since the K 3  is associated with a non-diverse path. These RTTs can be determined by actively probing each path from Source A and B to node  1910 . With all other flow characteristics begin equal, a flow control system will direct the traffic flow of interest over Path B (i.e., between SB and destination) because its total RTT is measured to be 40 ms (K 2 +K 3 ), which is more desirable than the RTT of 50 ms (K 1 +K 3 ) over Path A (i.e., between SA and destination). 
     At some time later, the convergence point at node  1910  is actively probed and K 2  is determined to have increased to 70 ms. But K 1  remains unchanged. Since Path B is now less desirable with a RTT of 90 ms than Path A, the flow control system will take appropriate action to route data flows of interest over Path A rather than Path B. For example, the flow control system (not shown) will announce that packets destined to address space  1951  should be routed via a router at Source A. Although RTT was monitored, any other flow characteristic, or combination thereof, can be monitored in accordance with the present invention. 
     In view of  FIG. 19A , and as a further example of the use of convergence points and their relationship to one or more destinations (e.g., address space), consider the following. In this case, node  1910  is no longer a convergence point and node  19 A 55  is determined to be the only convergence point associated with destination computing device  1952  having an IP address of 10.0.1.125/32. That is, both Path A and Path B converge at a node  19 A 55 . Since node  19 A 55  is uniquely related to destination device  1952 , the active probing of this node does not provide flow characteristics of paths between the source(s) and any other destination. Thus, in this example, active probing with respect to this destination cannot be reduced as is the case when node  1910  serves as a reference for address space  1951 . 
     An artisan of ordinary skill should appreciate that although only two sources are depicted in  FIG. 19A , any number of sources is suitable to practice the present invention. Further, each source node Source A and Source B can be, in some embodiments, routers designed to receive announcements from an exemplary flow control system. Sources A and B can be associated with or more entities and/or locations.  FIG. 25  illustrates an exemplary flow control system  200  where three source nodes (not shown) each are associated respectively with NSPs A, B, and C. In this case, the sources are associated with a single entity. Further, although machine  1952  is shown as a computer, one skilled in the art should recognize that any network element (e.g., router), subnetwork (e.g., LAN), server, or other destination item can be substituted for destination computing device  1952 . Although  FIG. 19A  (and  FIG. 19B ) describe specific addresses that in practice may not be used in a manner described herein (e.g., aggregated two address to form a /31 subnetwork), these Figures are for purposes of illustration and explanation. Further the present invention is not restricted to /32 addresses and prefixes, and can accommodate any number of addresses, such as /128. 
       FIG. 19B  depicts a relationship of destination devices and/or networks and an exemplary addressing scheme, such as IP addressing, to further illustrate how convergence points can provide a reference for a set of addresses. Although  FIG. 19B  shows only four computing devices, it should be understood that many more computing devices and/or destinations are possible. Destination devices  19 B 02 ,  19 B 04 ,  19 B 32 , and  19 B 34  are respectfully designated with specific addresses 10.0.1.125/32, 10.0.1.124/32, 10.0.1.126/32, and 10.0.1.127/32. Also, destination devices  19 B 01  and  19 B 99  represent the first and last machines of 256 computing devices that comprise an aggregated subnetwork identified as 10.0.1.0/24. Generally, contiguous specific addresses such as these are distributed within a common subnetwork address prefix, but for purposes of this example they are not. 
     In one embodiment, subsets of address (i.e., a smaller address space) are related to supersets of addresses (i.e., a larger address space) in a binary manner. The least significant byte  19 B 06  of address 10.0.1.125/32 is 01111101 and the least significant byte  19 B 08  of 10.0.1.124/32 is 01111100. It therefore can be said that the bit boundary (i.e., where the addresses differ only at one bit location) is the least significant bit of both bytes. If this bit is disregarded as “don&#39;t care,” or “X,” then both addresses can be described by a least significant byte  19 B 10 . Similarly, the least significant byte  19 B 36  of address 10.0.1.126/32 is 01111110 and the least significant byte  19 B 38  of 10.0.1.127/32 is 01111111. And if the least significant bit is also disregarded here as “don&#39;t care,” or “X,” then both addresses can be described by least significant byte  19 B 40 . Moreover, if the first two least significant bits can be disregarded, then all four specific addresses can be represented by least significant byte  19 B 50  and designated by address space  19 B 52  having an address/prefix of 10.0.1.123/30. Collectively, these addresses (i.e., address space) can be monitored by a convergence point.  FIG. 19B  also shows that all 256 computing devices can be aggregated in increasingly larger networks, such as from 10.0.1.0/29 to 10.0.1.0/24. It should be noted that address spaces related to a convergence point need not be of contiguous addresses or limited to only single bit boundaries (e.g., aggregation can occur for every even prefix, such as /30, /28, /26, etc.). 
       FIG. 20C  depicts an exemplary data structure  20 C 50  for leveraging the relationships between convergence points and addressing schemes to provide for route control in accordance with an embodiment of the present invention. In this example, data structure  20 C 50  includes specific addresses  20 C 51  relating to the computing devices of  FIG. 19C , which are populated in data structure  20 C 50 . Prefix flags  20 C 52  indicates whether any of the specific addresses  20 C 51  can be aggregated to an appropriate prefix level. CP  20 C 53  includes identified nodes that are convergence points. In this case, data structure  20 C 50  includes data representing that convergence point “w” of CP  20 C 53  is associated with each address  20 C 51  in records  20 C 56 . Addresses  20 C 51  associated with records  20 C 54  and  20 C 56 , however, do not include data representing a relationship to convergence point “w.” Rather, records  20 C 54  and  20 C 60  indicate that addresses 10.0.1.64/32 and 10.0.1.128/32 are not related to a convergence point. 
     A flow control system includes logic  20 C 20  to determine whether any of the prefix flags are to be set. Since all the addresses in records  20 C 56  share convergence point “w,” logic  20 C 20  operates to set the flags to an appropriate level of aggregation. However, since addresses 10.0.1.64/32 and 10.0.1.128/32 are not related to a convergence point, the corresponding convergence point field  20 C 53  is left vacant. 
     A flow control system operates, for example, to set the “/30” prefix flags since this level of aggregation sufficiently describes each of the addresses in records  20 C 56 . However, the /30 with respect to addresses 10.0.1.64/32 and 10.0.1.128/32 are not set. Logic  20 C 22  detects the set /30 prefix flags and then selects and associates a single route announcement of 10.0.1.124/30 to each address for routing data. That is, the flow control system includes logic  20 C 22  to associate an aggregated address space  20 C 55  (“Ag Add Sp”), if applicable. In the case of records  20 C 54  and  20 C 60 , no level of aggregation is set and these routes most likely will announced in accordance with conventional route selection techniques. 
     With address 10.0.1.124/32 to 10.0.1.127/32 aggregated, each packet  2541  of  FIG. 25  that leaves a particular source for one of the specific addresses will be matched to the /30 route and will be directed to the appropriate data path. The data structures shown in  FIG. 20C  are but one way to associate convergence points to address spaces for the purpose of obtaining an optimize route announcement. For example,  FIGS. 21A and 2113  depict an alternate data structure for another exemplary method of obtaining an optimized route announcement in accordance with another embodiment of the present invention. 
       FIG. 19C  depicts an exemplary network  19 C 00  including at least four paths from Sources A and B to destination address spaces  1951  and  1953 . Path A (i.e., SA between address space  1951 ) and Path B (i.e., SB between address space  1951 ), as well as convergence point at node  1910 , are discovered and identified in a manner similar to that of network  19 A 00  of  FIG. 19A . In  FIG. 19C , however, another network is discovered having an address space  1953  defined as 10.0.5.0/24, which includes router  1954  having an IP address of 10.0.5.192/32. The discovery of the network associated with address space  1953  could have been accomplished by passive flow analysis and/or other known discovery techniques, such as using manual methods, netflow, checkpoint, etc. Moreover, a second convergence point is present at node  1955 , which can be a reference for address space  1953 . 
     With a convergence point at node  1955 , the traffic flows along the path portions SB-B 48  (path defined by a portion from SB through nodes B 4  and BB 8  to a destination, where SB denotes Source B) and SA-A 3 -AA 7  (path defined by a portion from SA through nodes A 3  and AA 7  to a destination, where SA denotes Source A) can be monitored. And with a convergence point at node  1910 , the traffic flows along path portions SA-A 6  and SB-B 10  can also be monitored. With reference points for each address space, routing of data can be adapted to pick optimal paths according to the topological and/or geographic diversity between destinations. For example, suppose address space  1953  is located around Boston, Mass., U.S.A., address space  1951  is located around San Francisco, Calif., U.S.A., and the source is generally located in Los Angeles, Calif., U.S.A. 
     By using convergence points associated respective address spaces, data flows can be routed over the most appropriate paths. Between Source A and node  1955  (i.e., path of SA-A 3 -AA 7 ) and Source B and node  1955  (i.e., path of SB-B 4 -BB 8 ), active probing, for example, determines that the path of SA-A 3 -AA 7  is most desired to communicate data flows between the source in Los Angeles and the address space in Boston. Whereas, between Sources A or B and node  1910 , the path of SB-B 10  is the most optimum to route date between Los Angeles and San Francisco. 
     Without using convergence point methodologies, however, preliminary route selection techniques, such as those performed by BGP, will be employed. In this case, suppose that BGP preliminary route selection determines that the best way to route data from the source to address space  1951  is to announce a route 10.0.0.0/19 to, for example, a router at source A. That is, all packets matched against 10.0.0.0/19 will be routed out Source A. Although this may be appropriate for data flows to address space  1951 , this announcement requires data flows to address space  1953  to traverse path SA-A 6 -A 10 , which in this example includes path portions in Chicago, Ill. and New York City. Such detours increase transit time, latency, etc. Therefore, while some preliminary route selections by, for example, BGP may be appropriate for some data flows, such route selections hinder other data flows that are required to be routed in accordance with the preliminary route selections. Consequently, convergence point methodology in accordance with a specific embodiment allows for route selections that are the most appropriate for the destinations of interest. 
       FIG. 19D  depicts a network similar to that of  19 A 00  of  FIG. 19A , but includes another source, Source C, another path, and additional address space. Again, a convergence point is a node where at least two paths intersect. For example, node  1910  represents a convergence point for path A (i.e., SA through node A 6 ), path B (i.e., SB through node B 10 ), and path C (path defined by path portion SC through node C 8 , where SC denotes Source C). In discovering paths, and consequently convergence points, path tracing probes are sent along the paths to discover the available candidate paths. With respect to  FIG. 19D , paths A, B, and C represent the available candidate paths in the illustrated example. However, paths A, B and C are of varying number of hops. Path A, up to node/convergence point  1910 , represents 6 hops. In contrast, path trace probes Path B only reaches node  1920  after 6 hops from source B, thereby falling  4  hops short of node and convergence point  1910 . Path C, ultimately, never reaches the convergence point at node  1910 , but instead reaches node and convergence point  1930 , and requires 1 hop more than path A to node  1930 . 
     Thus, up through node and convergence point  1930 , path A represents the shortest route between the source and destination addresses or address space, since the hop-length is equidistant (1 hop, identified as  1940 ) from node and convergence point  1930  to destinations  1950  and  1960 . Beyond destinations  1950  and  1960 , there may be numerous addresses represented only as an aggregate of addresses or address spaces identifying several exemplary IP addresses and prefix, such as 10.0.0.0/24, 10.0.1.0/24, 10.0.3.0/24, 10.1.0.0/24, and 10.1.1.0/24. Further detail of this exemplary address space is depicted in  FIG. 19E  and discussed below. 
     Upon discovering the topology of the network routes including convergence points  1910  and  1930 , flow control system  200  ( FIG. 2 ) has discovered paths A, B, and C and identified convergence points at nodes  1910  and  1930 . Active probes can be generated by active calibrator  208  ( FIG. 2 ) and sent to nodes/convergence point  1930 . Responsive data representing node and/or path characteristics (e.g., RTT, loss, jitter, etc.) are generated by active probing and aggregated in a data structure such as a data table, although not limited necessarily to that specific structure (as discussed below in  FIG. 26 ). The data from path traces is analyzed to yield information, such as IP addresses and prefixes identifying a node and convergence point address and prefix. Active probes, in turn, result in retrieving responsive data representing characteristics such as RTT/loss, jitter, and other performance metrics. The responsive data, which represents performance characteristics, is stored in a data structure and referenced for comparison to previous like responsive data to determine whether a control change is required to modify the data traffic flow. If responsive data representing a measured performance metric matches the stored performance metrics, then no change has occurred and a control change may not be required. For example, if responsive data in relation to a specific node is measured to have a RTT of 1 Oms, and if that metric is equivalent to stored responsive data, then no corrective action is required. However, if a difference between the responsive data and the stored performance metrics (received from previous probing) is observed such that the difference is noncompliant or violates a specific policy, then a control change may be required by controller  205  ( FIG. 2 ). 
     Referring to  FIG. 19D , path A will be path traced along its complete length, through node and convergence point  1930 . However, active probing will stop at convergence point  1930  because it represents the closest convergence point prior to reaching destinations  1950  and  1960 . Path B will be path traced only as far as node and convergence point  1910 , as the path diversity with respect to Path A is equivalent to zero from that point onwards to the destination. That is, Path A and Path B share the same nodes from convergence point  1930  to the destination along which data is communicated. Path C will be path traced to point  1930  and, from that point onwards to the destination, will not be path traced. 
       FIG. 19D  also includes route information  1901  from the SA-A 6  path, route information  1902  from the SB-B 10  path and route information  1903  from the SC-C 8  path. This route information can be generated in accordance with any networking protocol, such as BGP, and provides a list of one or more routes for reaching destinations. Such route information is depicted in  FIG. 20A . In  FIG. 20A , routes received into the source from Source A (i.e., Next Hop A, or NH-A) is stored in exemplary data structure  20 A 10 . Likewise, similar routes to reachable destinations are recorded in data structure  20 A 12  (with respect to Source B) and data structure  20 A 14  (with respect to Source C). These data structures will be discussed further below in the context of  FIG. 19F . 
       FIG. 19E  illustrates a subset of probe points generated from active and/or path trace probing. In this figure, the data routes between convergence point  1930  and destinations  2010  and  2020  comprise 5 path portions, each of which can be a hop. Regardless of the number of hops or portions of paths A, B, and C prior to convergence point  1930 , from thereon, every path has an additional 5 segments between convergence point  1930  and destinations  2010  and  2020 , but within a smaller address space. Further, each of the IP addresses beyond destinations  2010  and  2020  are also shown. Sub-destinations, represented by network clouds  2030 ,  2040 ,  2050 ,  2060 , and  2070  can include IP addresses of specific destinations beyond destination points  2010  and  2020 . These points can represent ingress and/or egress points beyond destination points  2010  and  2020 . Examples of sub-destinations may be branch servers within a LAN or WAN, backup servers, hubs, or other components for servicing multiple destinations. The common path portions from convergence point  1930  to destinations  2010 ,  2020 , and  2030  through  2070  contain zero network path diversity. 
       FIG. 19F  is a more detailed network  19 F 00  showing at least nine paths from Sources A, B, and C to three convergence point related to specific sets of addresses. Similar to  FIG. 19D , address space  19 D 50 , which includes a small address space  19 D 51  of subsets of addresses identified by 10.0.0.0/24, 10.0.1.0/24, and 10.0.3.0/24, and address space  19 D 60 , which includes subsets of addresses identified by 10.1.0.0./24 and 10.1.1.0/24, are both associated to convergence point  1  at node  1930 . Further, the three paths from the sources via convergence point  1  to the destination can be identified by path SA-A 7 , path SBB 11 , and path SC-C 8 . 
     Further to exemplary network  19 F 00  is address space  19 D 12 , which includes subsets of addresses identified by 10.0.4.0/24 and 10.0.5.0/24. Address space  19 D 12  is shown to be related to convergence point  2  at node  19 D 11  and is reachable from Source A via path SA-AA 4 , from Source B via path SB-BB 5 , and/or from Source C via path SC-CC 4 . Similarly, address space  19 D 22  identified by 10.0.6.0/23 includes a smaller address space  19 D 23 , which includes a subset of addresses identified by 10.0.6.0/24. At least address space  19 D 23  is reachable from Source A via path SA-AAA 3 , from Source B via path SB-BBB 3 , and/or from Source C via path SC-CCC 5 , where each of these paths traverses through convergence point  3  at node  19 D 15 . 
     In one embodiment, address spaces  19 D 12 ,  19 D 51 ,  19 D 60 , and  19 D 23  have been discovered by passively analyzing traffic flows between those address spaces and the sources, whereas the candidate paths and the nodes thereof have been discovered by discovery probes. Address space  19 D 55  identified by 10.0.2.0/24 and address space  19 D 24  identified by 10.0.7.0/24, however, are not yet discovered. Hence, undiscovered address spaces  1913 D 55  and  19 D 24  are shown in broken lines. 
     In accordance with a specific embodiment, undiscovered address spaces and subsets of address thereof are presumed to be related to the convergence point associated with other address spaces in a binary, parent-child lineage. For example, undiscovered 10.0.7.0/24 is presumed to be a subset of 10.0.6.0/23, and undiscovered 10.0.2.0/24 is presumed to be a subset of 10.0.0.0/22 since other sibling address spaces 10.0.0.0/24, 10.0.1.0/24 and 10.0.3.0/24 share the same parent or superset of address spaces, as shown in  FIG. 21A . If, however, address space  19 D 55  identified by 10.0.2.0/24 is subsequently identified and found not to share the same convergence point (i.e., convergence point  1 ) associated with address space  19 D 51 , but rather shares convergence point  2  (or any other convergence point other than convergence point  1 ), then address space  19 D 13  will represent addresses identified by 10.0.2.0/24. 
       FIG. 20A  depicts exemplary routes received from the discovered candidate paths of network  19 F 00  of  FIG. 19F . For example, routes  20 A 20  received from paths SAA 7 , SA-AA 4 , and SA-AAA 3  are recorded in data structure  20 A 10  along with next hop  20 A 22  and other information  20 A 24  that might be used to make routing decisions. Next hop  20 A 22  information of structure  20 A 10  are all “As” because the associate routes are reachable from source A. The routes  20 A 20  reachable via Source B and Source C are recorded in data structures  20 A 12  and  20 A 14 , respectively. Routes received from Source B into, for example, a flow control system are associated with Next hop B, or NH-B, as shown in Next Hop B  20 A 22 , whereas routes received form Source C are associated with Next hop C, or NH-C, as shown in Next Hop C  20 A 22 . 
     Records  20 A 50  indicate that routes to 10.0.0.0./16 can be reached via any Next Hop NH-A, NH-B, or NH-C. Likewise records  20 A 70  indicate that routes to address spaces 4.0.0.0/19, 10.4.0.0/16 and 12.0.0.0/8 can be reached via all Next Hops A, B, and C. Again, such routes can be received by certain networking protocols, such as BGP. 
       FIG. 20B  illustrates how an exemplary flow control system in accordance with a specific embodiment uses route information that is recorded in exemplary data structures  20 B 12  and  20 B 60  to optimize the announcements of routes, which in turn, optimizes the routing of data between the source(s) and destination(s). In one example, a preliminary route selection process  20 B 10  is performed on the data representing routes (and accompanying information, such as next hop, etc.) from tables  20 A 10 ,  20 A 12 , and  20 A 14  in  FIG. 20A . Process  20 B 10  generates data representing routing information that can be populated in at least one data structure  20 B 12 , as shown in  FIG. 20B , which illustrates new relationships between routes  20 B 14  and next hop  20 B 16  information (as well as other information  20 B 18  known in the art), for example. In a specific embodiment of the present invention, process  20 B 10  is performed in accordance with BGP active route selection criteria. It should be noted that process  20 B 10  is optional in some embodiments and need not be required. 
     To illustrate the preliminary route selection process  20 B 10 , consider the selection of route 10.0.0.0/16 and its next hop of C, wherein process  20 B 10  operates to select routes to minimize the number of ASes that data traffic is to traverse. Although the tables of  FIG. 20A  indicates that routing data to these routes through either next hops A, B, or C (i.e., through sources A, B, or C) is possible, process  20 B  10  determines and selects data flows to these routes via next hop C because, in this instance, path SA-A 7  (from source A to address space  19 D 60 ) of  FIG. 19F  has the least number of transit AS hops (not shown) for the majority of routes to address space 10.0.0.0/16. Thus, this route is designated to route data through next hop C, which in some embodiments, can be a routing device from which data flows to the destination. Under preliminary route selection process  20 B 10 , this route (i.e., 10.0.0.0/16) will be announced to next hop C for route control. 
     For routes related to address space 10.0.0.0/16, consider that a convergence point (i.e., convergence point one) was found by route control process  20 B 42  to be related to a subset of addresses constituting that address. And suppose that routing data according to these more specific addresses (e.g., 10.0.0.0/24 10.0.1.0/24, 10.1.1.0/24, and 10.0.3.0/24) has been determined by route control process  20 B 42  to provide better data routing with respect to at least one flow characteristic (e.g., for enforcing a policy) than a more general route of 10.0.0.0/16. Further, route control determines that routing data to the more specific address spaces via source A rather than the preliminarily select source C would provide for optimum routing as determined, for example, by passive flow analysis. Route control process  20 B 42  would then select the more specific routes to route data and/or the optimum next hop, as indicated in data structure portion  20 B 30 . 
     Next, consider that a route control process  20 B 40  in accordance with a specific embodiment operates to further optimize data representing the route announcements  20 B 30 . Given the topological information available to an exemplary flow control process, such as the information described in regard to  FIG. 19F , the flow control process can operate to optimize the route announcement for routes 10.0.3.0/24 and 10.0.1.0/24. Since address space  19 D 50  of  FIG. 19F  is presumed to represent destination address spaces 10.0.0.0/24 10.0.1.0/24, 10.0.2.0/24, and 10.0.3.0/24, address space  19 D 50  can be identified as 10.0.0.0/22. Hence, data representing an updated route announcement  20 B 32  will be placed in data structure  20 B 60  as route  20 B 62 , which is used to route data flows and packets therein. For flows going to 10.0.0.0/24, 10.0.1.0/24, and 10.0.3.0/24, the packets destined to addresses represented as 10.0.0.0/22 will be directed accordingly via next hop A.  FIG. 21A  illustrates an example of how the optimized route can be determined. 
     In addition, route control process  20 B 40  operates to optimize data representing route announcements  20 B 30  for route 10.1.1.0/24. Since address space  19 B 60  includes 10.1.1.0/24 and 10.1.0.0/24, this address space can be identified as 10.1.0.0/23. Accordingly, data representing an updated route announcement  20 B 34  will be placed in data structure  20 B 60  as route  20 B 62 , which is used to route data flows and packets therein to address space  19 B 60 . Again,  FIG. 21A  illustrates how this route can be optimized for routing data. 
     In another example, consider that route control  20 B 45  determines that at least two subsets of addresses (e.g., 10.0.6.0/24 and 10.0.4.0/24) constitute the address space defined by 10.0.0.0/16. Further, suppose that route control  20 B 45  determines that data flows between the source and these address spaces are to preliminarily be routed via next hop A, respectively. In this instance, the more specific address spaces identified by 10.0.6.0/24 and 10.0.4.0/24 are related to (different) convergence point  2  (at node  19 D 15 ) and convergence point  3  (at node  19 D 11 ), respectively. According to the criteria of preliminary route selection process  20 B 10 , data flows to be routed between the source and the destination address space  19 D 23  of  FIG. 19F  are routed via next hop C, as indicated in the next hop field  20 B 16  of data structure  20 B 12  of  FIG. 20B . Similarly, data flows between the source and destination address space  19 B 12  are routed via next hop C as well. As in the other example, process  20 B 10  operates to minimize the number of ASes on path over which data flows. Using this criterion, path SC-CCC 5  via next hop C is selected and recorded in the next hop field  20 B 16  for routing data to address spaces 10.0.4.0/24 and 10.0.6.0/24. It is noteworthy that next hop C has been selected according to process  20 B 10 , regardless of the flow characteristics associated with these paths to address spaces 10.0.4.0/24 and 10.0.6.0/24. Hence, the default routing behavior may not provide for optimum data transport. 
     An exemplary flow control system employing route control process  20 B 40  is configured to further determine the optimum path in which to route data over, by way of, for example, passive analyzation techniques described herein. In this example, the flow control system uses route control process  20 B 45  to select paths that provide a path that either satisfies a specific policy, or is the optimum path in which to route data over. Consider that process  20 B 45  determines that next hop C provide for satisfactory data transport, but rather next hop B does provide for optimal data transport. In this case, process  20 B 45  selects next hop B and associates data representing next hop B into the next hop fields related to routes 10.0.6.0/24 and 10.0.4.0/24 in data structure  20 B 36 . 
     Route control process  20 B 50  determines that routes 10.0.6.0/24 and 10.0.4.0/24 are related to next hop B. That is, data flows between the source and destination address spaces 10.0.6.0/24 and 10.0.4.0/24 should at least route via next hop B. Process  20 B 50 , however, operates to further optimize the designation (for route announcement, for example) in which to route data by updating route field  20 B 62  with a substitute route of 10.0.4.0/22. In this case, with routes 10.0.6.0/24 and 10.0.4.0/24 related to the same next hop, the respective address spaces can be aggregated.  FIG. 24  illustrates how this updated route can be determined. 
     It should be noted that route control processes  20 B 40 ,  20 B 45  and  20 B 50  can be distributed throughout the flow control system and networks. In a specific embodiment, these processes and/or modules can reside in control module  2525  of flow control process  200  in  FIG. 25 . Additionally, data structures  20 B 12  and  20 B 60  can be located anywhere in the flow control system and networks. In a specific embodiment, data structure  20 B 12  resides in router  2545  in repository  2598  of  FIG. 25  and data structure  20 B 60  resides in router  2545  in repository  2599 . Such data structures can be combined and can be of any data structure known in the art. Also, these data structures can be located in separate routers. 
       FIG. 21A  illustrates an exemplary data structure  2100  for storing and comparing convergence point information for aggregating routes and information thereof, and to announce routes as determined by, for example, convergence point analysis. Data structure  2100  includes information relating to convergence points, relationships between convergence points and address spaces, discovered and undiscovered address spaces, and other similar information that describes features of network  19 F 00  of  FIG. 19F . Although data structure  2100  of  FIG. 21A  is represented as a multiple-level binary data structure, any other data structure known in the art that can relate information pertinent to topological-based route control, as described herein, is suitable to practice the present invention. In the example shown in  FIG. 21A , the data structure is a four-level, binary tree-type data structure shown as a subset of a larger thirty-two-level structure (or of any other number of levels), having parent-child relationships between various points on a network and corresponding levels of granularity of address prefix or netmask. The relationship between parent address space and child address space is illustrated, for example, in connection with the discussion of  FIG. 19B . 
     It should be noted that the example shown in  FIG. 21A  illustrates a portion of a more comprehensive data structure covering numerous relationships. This data structure represents exemplary structural relationships between data representing address space and data representing convergence points. These relationships facilitate combining subsets of address spaces to achieve the ability to determine common destinations under a single convergence point. Thus, the subsets of addresses can be monitored by a single probe. Some embodiments of the present invention avoid voluminous data traffic volume from probing all points above and below convergence points as found with conventional data flow control systems. 
     In a specific embodiment, each data cell of data structure  2100  is represented by a “circle” and is “linked” to a parent data cell representing a higher level of address aggregation and/or a child data cell representing a lower level of address aggregation. A data cell represents a portion of the network of interest, which can be described as an address space, for example, in terms of an IP address and a prefix (i.e., netmask). For example, data cell  2120  represents an address space defined by 10.0.0.0/22. Its parent data cell is data cell  2110 , which represents an address space defined by 10.0.0.0/21, and one of its child data cells is data cell  2122 , which represents an address space defined by 10.0.0.0/23. Data cells, such as  2120 , indicate their parent-child relationships as being “linked” by one or more lines, as the case may be. Further, each data cell contains data representing one or more convergence points that are associated with the represented address space. For example, data cell  2122  contains data identifying convergence point  1  (i.e., “I”) as related to the address space 10.0.0.0/23. As shown in  FIG. 19F , convergence point  1  at node  1930  lies on a path between the source and address space  19 D 51 , and again, provides a reference to address space  19 D 51  for actively probing the data path between the source(s) and destination(s). 
     In general, parent data cells represent an address space that includes an aggregation of its child data cells. For example, data cell  2122  is a parent cell to data cells  2124  and  2126 . The address spaces associated with 10.0.0.0/24 (data cell  2124 ) and 10.0.1.0/24 (data cell  2126 ) can be expressed as 10.0.[00000000].0/24 and 10.0.[00000001].0/24, respectively, where the third byte of the addresses is expressed in binary. When these address spaces contain the same convergence point (i.e., “1”), the address spaces can effectively be aggregated because convergence point  1  can be used to monitor traffic flow characteristics associated with the path(s) from the source to the destinations identified by both 10.0.[00000000. 10.0.[00000001.XXXXXXXX]/24 and 10.0.[00000001.XXXXXXXX]/24. Hence, the least significant bit of the third byte can be represented by an “X” as a “don&#39;t care.” Therefore, both address spaces can be aggregated and identified by 10.0.0000000X.0/24, which in turn can be described as address space 10.0.0.0/23 (i.e., data cell  2122 ). Once aggregated as 10.0.0.0/23, data flows destined to either address spaces associated with 10.0.0.0/24 and 10.0.1.0/24 can be routed according to the aggregated address by an exemplary flow control system, as shown in  FIG. 25 , and in accordance with the exemplary methods described in connection with  FIG. 20B . 
     Data cell  2110  is the parent data cell for each of the child data cells shown in  FIG. 21A , except for cells  2134 ,  2136 , and  2138 . The exclusion of data cells  2134 ,  2136 , and  2138  is discussed below. Data cell  2110  is also the highest level address space in the network topology illustrated in  FIG. 19F  and contains data representing three convergence points  1 ,  2 , and  3 . Parent data cells generally contain the convergence points associated with each of its child data cells. Data cell  2120  is also a parent data cell, but for data cells  2122 ,  2124 ,  2126 ,  2128 ,  2130 , and  2132 . Again, data cell  2120  is identified as address space 10.0.0.0/22 and contains a single convergence point  1  identified by an IP address of 66.185.23.1. 
     Likewise, data cell  2140  is a parent data cell for the data cells  2142 ,  2144 ,  2146 ,  2148 ,  2150 , and  2152 . But data cell  2140  contains data representing convergence points  2  and  3 , which are respectively identified with IP addresses 66.185.75.1 and 209.74.3.1. Because the address space 10.0.4.0/22 includes two convergence points, the performance of the paths between the source(s) and this address space related to data cell  2140  cannot be adequately monitored by a specific convergence point. Therefore, child data cells  2142  (i.e., 10.0.4.0/23) and  2144  (i.e., 10.0.6.0/23) will not be aggregated (without additional information, e.g., next hop) to form the address space represented by data cell  2140 . 
     As discussed above, data cell  2134  and its children data cells  2136  and  2138  are excluded from address aggregation into address spaces represented by data cells  2120  and  2110 . Data cells  2134 ,  2136  and  2138  are thus deemed “disjoint” because they are not direct descendants from either of data cells  2120  and  2110 . Data cells  2134 ,  2136  and  2138  do, however, contain the same convergence point  1 , as shown in  FIG. 19F . For data cells  2134  (i.e., 10.1.0.0/23) and its children to be in a direct parent-child relationship, these cells would be required to be at least linked to an address space identified by 10.0000000X.0.0/16, if, for example, all address spaces described by 10.0.0.0/16 are related to a single convergence point. 
     As discussed in connection with  FIG. 19F , address spaces  19 D 24  (i.e., 10.0.7.0/24) and  19 D 55  (i.e., 10.0.2.0/24) have yet to be discovered, unlike the other address spaces represented by data cells in  FIG. 21A . As shown in  FIG. 21A , the broken lines of the circle representing data cells  2130  and  2152  indicate that these are undiscovered address space. If discovered in the network topology by path trace probing, by passive flow analysis methodologies, or the like, data cells  2152  and  2130  will then populate data structure  2100  and will include their respective convergence points. For example, the IP address space of node  2130  (IP address/netmask=10.0.2.0/24) is shown to be undiscovered by at least the passive flow analyzer of the present invention  630  ( FIG. 6 ) and, therefore, is not populated in the data structure as no traffic is flowing to that destination. 
     In the case that address space  19 D 55  (i.e., 10.0.2.0/24) of  FIG. 19F  is discovered and found to be related to convergence point  1 , then in  FIG. 21A , the address space 10.0.0.0/22 of data cell  2120  remains a proper level of aggregation. In other words, convergence point  1  is sufficient to monitor all address spaces within 10.0.0.0/22. If, however, 10.0.2.0/24 is discovered to be address space  19 D 13  of  FIG. 19F , then this address space would be related to convergence point  2  (or any other convergence point) rather than convergence point  1 . Consequently, the address space 10.0.0.0/22 would no longer be an appropriate level of aggregation. 
       FIG. 21B  depicts an exemplary portion of data structure  2100  of  FIG. 21A  in response to discovering address space 10.0.2.0/24 related to convergence point  2 . As shown, data cell  21 B 30  contains data representing convergence point  2 . And its parent data cells  21 B 20  (i.e., 10.0.2.0/23) and  21 B 28  (i.e., 10.0.0.0/22) contain both convergence points  1  and  2 . With convergence point  2  being “pushed up” through data cells  21 B 20  and  21 B 28 , the address spaces related to these cells are no longer appropriate to aggregate to 10.0.0.0/22. Thus, the level of aggregation is “pushed down” through to child data cells having one convergence point. For example, data cell  2122  contains only convergence point  1 , which indicates that 10.0.0.0/23 is an appropriate level of aggregation. Data cells  21 B 30  and  2132  have only one convergence point (convergence points  2  and  1 , respectively). Therefore, 10.0.2.0/24 and 10.0.3.0/24 are appropriate levels of aggregation for addresses. 
     Data structure  2100  can reside in repository  2511  of an exemplary flow control system  200 , as shown in  FIG. 25 . Data structure  2100  of  FIG. 21A , however is not limited to reside therein and can reside any where within the flow control system and networks. In a specific embodiment of the present invention, flow control system  200  (and/or controller/control module  2525 ) of  FIG. 25  and data structure  2100  of  FIG. 21A  are used to govern route control process  20 B 40  of  FIG. 2013 , for example. 
     In one example, flow control system  200  operates upon the specific route that is associated with 10.0.3.0/24 of data structure  20 B 30  (e.g., portion of 201312). To determine whether this specific route is optimized in its level of aggregation, the flow control system determines that first it is not optimized. To provide an optimized level of aggregation in which to announce (and route data), the flow control system determines a data cell that corresponds to the specific route&#39;s level of aggregation. That is, specific route 10.0.3.0/24 is matched to data cell  2132  of  FIG. 21A . Then, the flow control system moves up through the parent-child linkages until a parent (or grandparent, etc.) data cell represents the largest number of addresses (i.e., largest address space) while containing one convergence point. In this case, that is data cell  2120 . Therefore, the proper level of aggregation represented by data cell  2120  is 10.0.0.0/22, which is placed into data structure  20 B 60  in the form of route update  20 B 23 , as shown in  FIG. 2013 . The above process is similarly followed for the specific route associated with 10.0.1.0/24 of data structure  20 B 30 . 
     In another example, the specific route related to 10.1.1.0/24 of data structure  20 B 30  is processed by route control process  20 B 40  of  FIG. 2013 . This preliminary route is matched against data cells in data structure  2100 , which in this example, resides in repository  2511 . Consider that flow control system  200  matches the preliminary route to the address space of 10.1.1.0/24 at data cell  2138 . The flow control system then moves up through the parent-child linkages until a parent (or grandparent, etc.) data cell represents the largest number of addresses (i.e., largest address space) while containing one convergence point. In this case, data cell  2134 , which represents 10.1.0.0/23, is found to be the largest address space in the parent-child linkage. Hence, address space 10.1.0.0/23 is the appropriate address and prefix to use to route data from between the source and one or more destination within 10.1.0.0/23. 
     Returning to the first example where the proper level of aggregation was determined to be 10.0.0.0/22, which was placed into data structure  20 B 60  in the form of route update  20 B 23  shown in  FIG. 20B . Next suppose that an address space 10.0.2.0/24 related to convergence point  2  is discovered, as shown in  FIG. 21B . Flow control system  200 , whether periodically or in response to a certain event, then detects the discovery and adjusts the proper levels of aggregation as discussed above in connection with  FIG. 21B . The flow control system then will withdraw the 10.0.0.0/22 route and will replace it with 10.0.0.0/23, 10.0.2.0/24 and 10.0.3.0/24, which are appropriate levels of aggregation as determined above. In a specific embodiment, the updated routes 10.0.0.0/23, 10.0.2.0/24 and 10.0.3.0/24 are placed in a data structure  2599  of router  2545  of  FIG. 25  for providing for appropriate routing of data. 
     As actively probed convergence points reveal changes in network performance, other convergence points can be substituted when data paths are modified to provide optimum data routing. Theses changes affect one or more parent-child relationships in data structure  2100 , and thereby change the proper levels of aggregation for numerous address spaces. Consequently, exemplary data structure  20 B 60  of  FIG. 20B  will change to accommodate new routes. 
     Thus, route control in accordance with an exemplary embodiment of the present invention uses tree-oriented analyses such as those illustrated and described as in  FIG. 21A . By analyzing a series of points in a determinate fashion, the number of active probes that are sent to specific nodes is minimized, thus reducing the amount of route control data traffic and increasing the overall efficiency of data routing and control. Using a data tree structure to analyze convergence points, the construction of efficient network data paths is possible by analyzing the relationships between each point (node) to identify the shortest prefix, which would indicate a convergence point related to the largest set of addresses in an address space. This is the prefix length that can be announced in order to adjust the primary data path in reaction to a network degradation incurred at a destination point. 
     It should be noted that other data structures, such as described in  FIG. 20C , and methods of route control by way of optimized routing announcements (to the egress routers), for example, are within the scope and spirit of the present invention. 
       FIG. 22  is a control flowchart  2200  illustrating an example of the method of determining characteristics associated with each hop and point. For example, in  FIG. 19D , each point along path A can be path trace probed in sequence, thereby generating responsive data which is stored in a repository or other data structure for constructing a map of the network topology. The example shown in  FIG. 22 , a path trace is started on one or more candidate paths in step  2210 . In step  2220 , the IP address of each hop can be recorded in a data structure and checked against previously recorded data. At  2230 , each hop discovered by a returning probe is checked to see if it has either been probed or recorded previously. At decision point  2240 , the decision as to whether each hop has been seen (e.g., probed and/or recorded) previously is determined by comparing the probe-generated information (such as an updated IP address) to stored data such as archived IP addresses contained within a data structure. If the hop has been previously probed and/or recorded and information matches previously recorded hops (signifying the discovery of a convergence point), the candidate path trace is halted and the sub-convergence point is recorded in step  2250  and  2260 . 
     If the hop was not seen (e.g., probed and/or recorded) previously, another decision point as to whether the path trace should be ended occurs at step  2270 . If, however, the candidate path trace reveals a sub-convergence point, it is recorded in a data structure at step  2260 . If the hop has not been probed or recorded previously, then another condition-determining decision occurs at step  2270 . In step  2270 , one of four possible conditions may result in the termination of the overall path tracing condition. The first condition is whether the probe has reached its intended destination. The second condition is whether a predetermined number of probes fail to generated responsive data such as convergence point characteristics, data, or parameters. Third, if a routing loop is encountered, the path tracing condition will be ended. Fourth, if unknown ICMP code is encountered, then the path trace is ended. If path trace probing is halted, then the process is done as reflected in step  2280 . The number of failures to be seen before ending the probe can be pre-set as a stored rule for use by the active calibrator  208  ( FIG. 2 ), either by the system, user or another means.  FIG. 23  shows logic that can further reduce the number of path trace probes to a destination, further reducing the possibility of triggering security measures. Logic processes, as described above, halt all path traces, including the first probes to reach the destination, except when all candidate paths have a convergence point. 
       FIG. 23  illustrates an exemplary control flowchart  2300  for a method further describing the end condition of step  2270  in  FIG. 22 , in accordance with another embodiment of the present invention. In this method, probe points such as convergence points are discovered and/or established regardless of whether transit AS or destinations filter or prevent probe information from returning back. More specifically, the method establishes an alternate point in which to probe if either a transit AS or a destination prevents the generation of information in response to probes. In one embodiment, the method establishes as an alternate probe point a node one hop removed from a non-responsive node. Again, a sequential path trace is started in step  2310 , for example, by controller  205  of  FIG. 2 . A probe is sent to a next hop in step  2320  and, in step  2330 , determines if the probe provides data about nodes along one or more paths in response to the path trace probe. If responsive data is received, then the path trace to a specific node is considered complete in step  2370 . 
     If there is no answer to the path trace, then the system must determine the then-current location of the probe. In step  2340 , the flow control system determines if the target node (i.e., a convergence point) was non-responsive to the probe and, if so whether it was proximate to an intended destination. By comparing characteristics of a particular node to data stored in traffic repository  221  ( FIG. 2 ), controller  205  can determine whether the IP address, among other characteristics matches a recorded IP address for a known transit AS. Controller  205  can also determine whether the probe has reached its probe depth, or whether the probe has failed. For example, a probe depth of “Y’ might specify that three failed probing attempts are allowed before probing is halted. The probe depth specifies a limit which prevents excessive probing from, for example, triggering security measures to be implemented. Examples of security measures which might be implemented can be similar to those in response, for example, to a denial of service attack. If the target node is nonresponsive then the system, in step  2350  determines whether the probe reached its destination or in the transit AS of the destination, which is the AS directly upstream from the destination. Generally, the upstream AS can be identified, for example, by the BGP daemon (described below in connection with  FIG. 25 ). If a probe is non-responsive, then this may indicate a filtered address or “black hole” which, when recorded in a data structure such as a repository or database, can indicate a network problem, latency, or obstruction, thus invoking alternate data routing and route control to determine an alternate path. 
     If an answer is received, then the system determines if the hop reached its desired destination or sub-convergence point at step  2360 . If it is the last hop, then the path trace is recorded as completed. A new active probe session is started, targeting the convergence point whose IP address is the last recorded convergence point in the repository or other data structure as shown in step  2370 . If the hop is answered from step  2330  and if the hop is at its destination convergence point, the path trace is considered complete. If not, then the next probe (i.e., incremental time to live) is sent, restarting at step  2320 . 
     Additional logic shown in  FIG. 23  can be applied using data (e.g., nonresponses, lack of response to particular probes, etc.) from a data structure to determine if filtering is occurring close to the destination or if the filtering is happening in the middle mile. If the filter is seen close to the destination the system may not be able to resolve a complete data path to the destination filters. If the problem is seen in the middle mile the system can continue to look for valid hops after the maximum number of probes is sent. In some embodiments, a system wide limit can be set as a redundant measure to handle cases of routing loops or other pathologies that occur in the network. 
       FIG. 24  shows an another exemplary data structure in accordance with another embodiment of the present invention that incorporates, for example, source-specific information such as “next hop” information. Next hop information can supplement exemplary convergence point methodologies according the present invention. “Next hop” is information related to a network path portion or node located one hop from a particular node (e.g., source node). In one embodiment, next hop information can include identifiers of egress router that are located on specific paths between the source node and one or more destination addresses. A next hop can be an address (i.e., identifier) from a routing table or other data structure that directs data traffic flow (i.e., routing table of BGPd as shown in  FIG. 26 ). For example, a router may have an IP address of 66.185.23.1 and designated by “NH-A.” Data traffic routed over this link or NSP will have a next hop address of “NH-A” in the local routing table. This router represents as a node or point may be associated with convergence points within a specific address space, as designated and announced by specific prefix length (e.g., /19). However, next hop information is not necessarily associated with convergence points. In another embodiment, next hop identifiers A, B and C, as described herein can refer to Source A node (e.g., router), Source B node, and Source C node, respectively. 
     The destinations in the network of  FIG. 21A  are also reflected in  FIG. 24  as  2424 ,  2426 ,  2430 ,  2436 ,  2438 ,  2446 ,  2448 ,  2450 , and  2452 . Next hop information for each of these destination prefixes (e.g., 10.0.3.0/24) can be determined, in one embodiment, by using the routing table of BGPd on the current internal routing table of controller  205  ( FIG. 2 ). In the example of  FIG. 24 , there are two potential routes with two potential next hops, indicated by “NH-A” and “NH-B.” An exemplary flow control system, for each destination network of  FIG. 24 , does a route lookup and stores next hop information in a repository or storage application with convergence point information. 
     Adding next hop information to the data structure  2   100  of  FIG. 21A , as shown in  FIG. 24 , can be used to select the appropriate prefix length that should be announced (e.g., to network routers identified by next hop information). Consider data cells  2142  and  2144  of  FIG. 21A , which each have different (but one) convergence points. In accordance with an exemplary convergence point methodology, the specific address spaces identified as 10.0.4.0/23 and 10.0.6.0/23 are to be used for routing data. However, consider the next example where next hop information is used to supplement convergence point information. 
     As shown in  FIG. 24 , suppose two destination address spaces prefixes at 10.0.4.0/23 and 10.0.6.0/23 share different convergence points ( 2  and  3 ) yet share the same next hop (NH-B). Therefore, it is appropriate to announce 10.0.4.0/22 associated with data cell  2440  to network routers. However, if network degradation occurs thereafter at 10.0.5.0/24 and requires resolution by routing over NH-A rather than NH-B, the aggregation point is lowered (“push down”) to 10.0.4.0/23 because it shares convergence point  2  via next hop NH-A. Address space 10.0.4.0/23 becomes associated with the new announced route to network routers. Destination 10.0.6.0/23, however is, still is routed over NH-B since the problem did not affect this portion of the address space (since it is related to a path associated with convergence point  3 ). This routing can be affected by leaving the more general route of 10.0.4.0/22 via NH-B in place (the more specific 10.0.4.0/23 over NH-A will take precedence in the routing table) or 10.0.4.0/22 can be withdrawn and replaced with 10.0.6.0/23 over NHB. 
     Data structure  2100  of  FIG. 24  can reside in repository  2511  of an exemplary flow control system  200 , as shown in  FIG. 25 . Data structure  2   100  of  FIG. 24 , however it is not limited to reside therein and can reside any where within the flow control system and networks. In a specific embodiment of the present invention, flow control system  200  (and/or controller/control module  2525 ) of  FIG. 25  and data structure  2100  of  FIG. 24  are used to govern, or embody, route control process  20 B 50  of  FIG. 2013 , for example. 
     In one example, flow control system  200  is used to control the routing of data over network  19 F 00  of  FIG. 19F . The flow control system determines that after passively monitoring the data traffic over paths from each source to each address space  19 D 12  (i.e., 10.0.4.0/24) and  19 D 23  (i.e., 10.0.6.0/24) that paths passing through Source B have the most desirable path performance characteristics (e.g., favorable in terms of RTT, loss, latency, etc). As shown in  FIG. 20B , the route control process  20 B 45  of flow control system  200  operates to override the preliminary next hop information, as determined by the preliminary route selection process  20 B 10 . In this case, next hop C, which is associated with 10.0.6.0/24, is changed to next hop B in data structure  20 B 36 . Similarly, next hop C associated with 10.0.4.0/24 is changed to next hop B in data structure  20 B 36 . 
     Route control process  20 B 50  of the flow control system further operates on route and next hop information from  20 B 36 . To determine whether the preliminary route(s) are optimized in its level of aggregation, the flow control system determines whether it is not optimized. To provide an optimized level of aggregation in which to announce (and route data), the flow control system determines a data cell that corresponds to a preliminary route&#39;s level of aggregation. 
     The route control process  20 B 50  evaluates the preliminary route(s) of 10.0.4.0/24 and 10.0.6.0/24 against the address spaces associated with the data cells of  FIG. 24 . Then, the flow control system moves up through the parent-child linkages until a parent (or grandparent, etc.) data cell represents the largest number of addresses (i.e., largest address space) while containing, for example, one convergence point. For preliminary route 10.0.4.0/24, the largest address space containing just convergence point  2  in this example is data cell  2442 . For preliminary route 10.0.6.0/24, the largest address space containing just convergence point  3  in this example is data cell  2444 . Also, route control process  20 B 50  determines whether data cells  2442  and  2444  and their respective address spaces relate to one next hop identifier. In this case, it is NH-B. Although children nodes  2442  and  2444  of parent node  2440  have different, albeit one, convergence points, nodes  2442  and  2444  are related to the same next hop identifier NH-B. Therefore, the proper level of aggregation represented by the parent data cell  2440  is 10.0.4.0/22, which is placed into data structure  20 B 60  in the form of route update  20 B 38 , as shown in  FIG. 20B . 
       FIG. 25  illustrates an exemplary network  2500  coupled to a flow control system in accordance with an embodiment of the present invention. A data repository  2510 , router  2515 , passive flow analyzer  2520 , control module  2525 , daemon application  2530 , repository  2511 , source router  2545 , and intermediate nodes  2547 . Destination nodes  2550  are reached via network A  2560  and network B  2570  by routing data traffic flow over Internet backbone  2580  through convergence point  2585 . Destination nodes  2550  can also represent intermediate nodes in a destination AS. Beyond convergence point  2585 , destination nodes  2550  are encompassed by address space  2590 . In exemplary embodiments of the present invention, a third-party vendor may provide the BGP daemon application  2530  for protocol-driven standardization of data networking communications. BGP daemons may be written in various languages and formats such as C or C#, generally incorporating the latest versions of BGP, such as BGP4. One having ordinary skill should appreciate how to script a BGP daemon suitable to practice the present invention. However, it is foreseeable that other protocols may replace BGP and the description herein is not intended to limit daemon application  2530  to only those incorporating BGP. Other standards bodies such as the IETF may release new RFCs for new protocols and alternative embodiments of the present invention may use these daemons. 
     Along candidate paths are nodes  2547 , shown passing through network A  2560  and network B  2570 . Node  2589  is found along candidate data routes between source router  2545  and convergence point  2585 . Beyond convergence point  2585 , several destination nodes  2550  exist as represented by aggregate address space  2590 . Internet  2580  is a typical electronic network which connects to network A  2560  and network B  2570 , but may be embodied by alternative electronic networks such as a LAN, WAN, or other type of distributed computing network. 
     Operating in a manner similar to a first-order data filter that can analyze prefix addresses for problems, which might degrade or adversely affect data routes. Probe signals that are generated to provide diagnostic data on data routes are sent to the control module  2525 . 
     Repository  2511  is but one vehicle to store data described herein according to any appropriate data structure. Additionally, although router  2545  is shown to be one routing device, the routing functionality can be distributed across any number of routing devices. Moreover, data structures  2598  and  2599  can be combined, or alternatively, data structure  2598  can be modified by the flow control system so as to be transformed into data structure  2599 . One having ordinary skilled in the art should recognize that the flow control system and peripheral network elements can be arranged in any fashion, functionally and structurally, to practice the present invention. 
       FIG. 26  is an illustration of an exemplary data structure  2610 , which can be implemented by a routing table, repository, database, or any of a number of other data structures. Data structure  2610  may be used to store data and other information for use by flow control system  200  ( FIG. 2 ). Data such as IP addresses, prefix/netmask, latency, next hop in information, next hop out information, convergence point identification, user configurable operating parameters, and other data may be stored in data structure  2610 . Data gathered in response to path trace and active probing may also be used. Using recorded information such as IP addresses or conditions recorded in data structure  2610  enables the creation of a topological network map, from which efficient data routes are constructed. Candidate path convergence point IP addresses are stored in data structure  2610  for topologically-mapping network data routes. Aggregating IP addresses of convergence points between a source and a destination node or point enables efficient data route control in accordance with an embodiment of the present invention. 
     In the simplest embodiment of route control, a probe point can be set to be one hop prior to a destination (as discussed above) or a point along a data route where, for example, probes fail to generate responsive information because they are continuously filtered such as described in connection with  FIG. 23 . In another embodiment that uses convergence point analysis, the network probe point is the first common hop along all of the candidate paths. By sending active probes to each of these points, any responsive information received by the system is recorded in data structure  2610  for use in constructing a topologically-aware network map. Again, as convergence points represent points in the network where path diversity is zero, these points are mapped by the present invention to determine an efficient data route. 
     The scaling benefits of an embodiment of the present invention are illustrated in the graph of  FIG. 27 . Scaling benefits may occur within a network aggregation such as the one illustrated in  FIG. 19D  where one or more convergence points such as  1930  exist.  FIG. 27  illustrates the number of destination networks behind the lowest-level prefix convergence points observed over an hour, in accordance with an embodiment of the present invention. The effects are fairly uniform with an average of 100 networks behind each convergence IP. Measuring just the convergence point yields a 100 to 1 gain in scaling or efficiency, that is, a single measurement today can do the work of 100 measurements of the past. When the number of NSPs is reduced, some destinations may observe little or no network path diversity. High density convergence points may emerge and, when probing to these high density convergence points, they may be only a few hops away. The majority of the network path may have zero network path diversity. Thus, convergence point analysis can effectively measure the level of path diversity offered by the correct set of NSPs. 
     Further, end-to-end measurements are good at indicating deviations from normal operating parameters and detecting performance problems. However, effects on non-diverse portions of a path can cloud end-to-end provider/NSP comparisons. End-to-end measurement and control techniques such as TCP probes, ICMP/UDP probes that traverse non-diverse portions of the path, measurement techniques such as web objects and other application based measurements are often confused by last-mile congestion. Because of queuing and other effects, any measurements through congestion can vary by large amounts (e.g. latency that varies by +/−100s of ms is not uncommon). If the congestion occurs on a non-diverse, “last mile” link, any given provider may appear to have substantially better or poorer performance for any given measurement due to these random effects. Thus, last-mile conditions, which cannot be solved with routing, may cloud the eventual routing decision that is made based on these poor and highly variable measurements. Whenever possible, more accurate measurements can be made by avoiding the shared portion of the route or path. 
     This effect is illustrated in  FIG. 28 .  FIG. 28  shows a route where a performance problem (high latency, +63 ms, at the highlighted link) occurs beyond the convergence point. This high latency is a problem that cannot be solved through routing, as every available path traverses the shared hop where the problem occurs. Any technique that measures through that congestion will experience highly variable measurements as described above. It is not possible to make an accurate decision using end-to-end measurements under these circumstances. Measuring instead to the convergence point allows an effective assessment of all the candidate paths relative to the diversity being offered along the route. By measuring up to the point of the path that can be controlled by routing, the embodiment is not subject to the variable effects on the non-diverse path. Thus being aware of these situations, the product is prevented from making route changes that attempt resolution of problems it cannot effectively solve. 
     Unless a flow control system recognizes the above-discussed situations by measuring only the portion of a path that is relevant (i.e., up to a convergence point), spurious route changes and churn can occur. As discussed, where congestion exists, the variance in latency can be very-high. For example, one sample may vary by 100s of ms from a next, to the same destination, as part of the same flow. Using an embodiment of the present invention, these effects can be isolated to a last-mile link beyond the convergence point where no path diversity exists. While passive analysis observes these as performance problems, embodiments of the present invention can recognize that a data flow is already on the best-performing path available. If the route control product assesses candidate paths in an end-to-end manner such as TCP probes, web objects or destination-based probes, the candidates would appear to differ by the same 100s of ms, packet-by-packet. This will cause some paths to appear to perform better at some times and other paths to appear to perform at a degraded level at other times, resulting from last mile effects. Routing changes based on such measurements may result in needless changes, route churn, or other spurious and ineffectual actions. 
     Convergence point analysis presents a common probe point for all destination prefixes seen beyond this point. Using this analysis significantly reduces the probe volume that must be sent because a single probe result can be used for all downstream destination prefixes. Measured “middle mile” or diverse path performance to the convergence point is relevant for all of these prefixes. 
     Additionally the type of route view shown in  FIG. 28  is useful for the network operator or engineer, especially when troubleshooting problems related to a specific destination. This reporting capability is an important aspect of the embodiment. The view into each route shown in  FIG. 28 , including the individual links and relative performance over each link allows the operators to quickly assess each route and understand the intermediate providers that are traversed, the relative performance of each of those providers, where the route converges, what percentage of the route is actually diverse over the current set of providers, as well as a quick indication of any and all problem areas such as poor performance that were encountered on the path. In general, such a report is very useful not simply for troubleshooting actual problems, but understanding every detail about how the providers are able to reach this particular destination. By storing such reports over time, it is possible to find and report on historical intermediate route changes for each destination. Additionally the ability to detect certain events deep in the network allows the system to monitor the egress network all the way to each destination. Such a capability is common for local area networks, but no system exists that correlates such data over the wide area network. 
     This in-depth topology analysis allows the system to determine some root cause analysis for each network event or performance problem that is seen. Events include but are not limited to routing loops, black holes, high congestion, peering problems, and other routing anomalies. By observing these effects historically it is possible to report on the temporal nature of each of these events and report on the overall impact each event had, both in terms of the number of destinations affected, the duration of the event, and how much traffic volume was impacted throughout the event. This event-based reporting is very useful for the network operators to understand the overall impact each network event had on the operations and applications. It is also possible to highlight the actions that the embodiment took to isolate and route around the problem. Such reporting capabilities serve to highlight the effectiveness of the route control products in realizing performance improvements and isolating the impact of various network events. 
     As discussed,  FIG. 28  illustrates the overall diversity that is offered to the indicated destination. This diversity can be expressed as a percentage of the total path. For example, in  FIG. 28 , two of the three paths have 6 diverse links and 5 non-diverse links, each being (6/11=0.54) roughly 54% diverse. The remaining link has 5 diverse and 5 non-diverse links and is thus 50% diverse. Averaging all of these together yields a total diversity of 53% to this destination. Thus there is a good chance (47%) that a problem will occur on this path that cannot be resolved with route control. If this is not acceptable diversity, the network planners might consider adding another provider that converges closer to the eventual destination, thus offering better reach to that destination, and lowering the risk that any given network failure will impact the application. Thus, as a capacity planning tool, understanding the available path diversity to all destinations allows the operators and network planners to assess the risk of an “unsolvable” problem occurring. In general, low path diversity=high risk of such problems. 
     Collecting the path diversity calculations for all of the observed routes allows for a general assessment of the overall path diversity being offered by the providers. This information can be collected and calculated from the topology assessment and reported to the user for network planning purposes.  FIG. 29  illustrates one embodiment of such a report. In  FIG. 29 , all of the paths to the destinations of interest are assessed for diversity and plotted from 0% diverse to 100% diverse. The line in  FIG. 29  represents the number of destinations or prefixes that correspond to the various diversity percentages. Each destination can be weighted by the amount of traffic being sent to that destination over the duration of the report as shown by the bars of the chart. Thus, at a glance, the network planner can assess the overall path diversity available over the current provider selection and understand how well the mix of providers in use is able to reach the important destinations of the users. 
     Furthermore, as shown in  FIG. 30 , a breakdown of the total path length for each percentage is possible, making it easy to spot aberrations based on abnormally short or long path lengths.  FIG. 30  illustrates the path lengths for a subset of the paths shown in  FIG. 29 . Although any subset can be selected,  FIG. 30  illustrates the path lengths for the paths shown in  FIG. 29  having 50%-75% diversity. Showing the total hop count, again weighted by destination volume, allows the operators to easily see how far the physical path length of each destination is by volume. As a supplement to these reports, it is possible to plot the top Autonomous Systems (i.e. destinations) that are in each of the operating regions. This allows the operators to easily see which destination networks are getting poor path diversity. If those destinations are important enough, additional or different network connectivity can be brought in that is better able to reach those important networks. 
       FIG. 31  represents the volume of traffic to and the distance of a number of destinations and reflects another possible report that can be generated once the topology is known. A common analysis by network engineers is to understand which destination Autonomous Systems (AS) are sending or receiving the highest volume of traffic and the distance of those destinations. If an important destination is far away, efforts can be made or changes in network connectivity can be made to bring those destinations closer to the local application.  FIG. 31  is one possible way to represent this information, though other similar views to addresses these issues are possible. 
       FIG. 31  shows the top N destination Autonomous Systems by volume. The number N can be configured and in this example the top 30 are shown and identified by name (e.g. GIGAMEDIA-AS-AP, AS3215, KIX, etc). The thickness of the line to each destination Autonomous System name represents the relative volume of traffic. The distance of the destination is shown as the number of AS hops (1, 2, 3, 4, 5, 6) traversed to reach the destination. This is equivalent to counting the large ovals of  FIG. 28  on the way to the destination, each of which represents an intermediate AS hop. The total volume of all N top destinations is represented by the thickness of the line at the far left of the figure. 
     This figure allows the operators and engineers to see at a glance which destinations are important by volume and the distance to those destinations, in terms of intermediate providers traversed. An ability to mouse over each line or destination name to obtain numerical volume using a ‘tool-tip’ menu is an aspect of this report that is not illustrated.  FIG. 31  is an effective aggregation of the topology information collected by the underlying system to analyze aspects of the existing network such as connectivity and load. 
     Referring back to  FIG. 19D , the results of the topology discovery (or path trace) probes are recorded for detecting future network degradations at points related to one of the destination prefixes (10.0.0.0/24). Path traces are started over paths A, B, and C recording the path hop by hop. With convergence point analysis only the probes over candidate A reach the destination, unless a change in the topology is discovered or no convergence point exists, in which case the probes will be sent to the destination(s). This reduces the volume of traffic that can cause security alerts at the endpoints.  FIG. 22  shows the control flow process for path tracing. 
     A common problem in conventional topology discovery probes results when intermediate service providers filter the response to traceroute packets. This results in several hops within that provider that do not respond. Conventional topology discovery probes may confuse these filters with security filters that are commonly implemented near a destination. If the approach is to continue increasing the time-to-live (TTL) rate of active probing until a valid hop is returned, this will not generate a response when the trace is hitting a filter at the destination. A simple embodiment is to administratively set a depth at which the system will give up if no valid hop returns. For example, a configuration that sets the max loss filter at 3 hops would halt the trace if three concurrent hops did not return a result. At the destination the filtering device will see the packets for all three hops and may trigger security notifications to the system administrator or cause pre-set security reactions to occur. If the filtering occurs in the middle mile, the problem may cause only a small portion of the path to be recognized and thus minimize the optimization of the data route. 
     Returning to  FIG. 19D , the sub-convergence point  1910  and the convergence point  1930  are recorded. When additional prefixes are discovered (such as point  1950  at IP address/prefix 10.0.3.0/24 and point  1960  located at IP address/prefix 10.1.0.0/24) the path trace methodology discovers the same convergence point  1930  at IP address 66.185.23.1. This is added to the repository of convergence points and a single probe is generated and sent to convergence point  1930  for 10.0.0.0/24 whereupon it is recorded as a result to 10.0.1.0/24, 10.0.3.0/24, 10.1.0.0/24, and 10.1.1.0/24, all of which have the same convergence point. This greatly reduces the volume of probe traffic over conventional methods of route control. In other embodiments of the present invention, convergence point analysis can be used in data networks where the data network provides the communication means, such as physical inter connective links comprising copper wire, fiber optic cable, or the like, for transmitting and receiving signals. Similarly, wireless communication means, such as radio waves or the like, are also understood to provide means to transfer. information from a source to a destination. 
     As is well known in the art of network communications, data networks are configured to communicate electrical information, such as a computer data signal comprising data (e.g., binary data bits) superimposed upon a radio or any other carrier wave. A person having ordinary skill in the art would appreciate that a carrier wave is electromagnetic energy propagated from a source by radiation, optical or conduction waves and is suitable for embodying an information-bearing signal, such as a computer data signal. In one embodiment, a carrier wave behaves, or is modulated, according to a network protocol, such as Ethernet, IEEE 1394, TCP/IP, or any other communication protocol, so as to include computer data information. In some embodiments, the computer data signal includes a computer program for practicing the present invention. 
     The carrier wave can be, for example, a direct current, an alternating current, or a pulse chain. In modulation of the carrier wave, it may be processed in such a way that its amplitude, frequency, or some other property varies so as to embody data for transfer. 
     It should be noted that the route control processes discussed above were separated to emphasize the functionality of the processes, and that theses process can be constituents of the processes underlying the flow control system and/or the controller. Also, the data structures described above were also separated to better illustrate certain aspects of the present invention. In one embodiment, a single repository and/or data structure comprise each of the data structures described above. 
     Although the foregoing description uses convergence points as exemplary probe points or proxy points, the invention is not limited to the use of convergence points. Other means of point identification are contemplated by the invention and include using other intermediate hops along the data path, common address points inside a destination network block, such as the broadcast address, common network infrastructure elements, such as gateway routers or DNS servers, techniques, such as triangulation of third-party measurements, as well as other similar means. For example, a proxy point can be selected as the last known hop along a data path before an administrative boundary blocks the measurement. Common administrative boundaries, such as network firewalls block measurements to the destination end point. In order to measure the destination, the probing element typically has to “back off” by one hop in order to collect data and avoid security mechanisms or firewalls. This “N−1” hop is the last point on the data path that will respond to measurement and is an example of a very simple proxy point for the destination. Other common proxy points are well-known addresses inside a destination network. Addresses, such as the gateway address, typically “.1” of any address block (e.g. 24.0.16.0/24 uses 24.0.16.1 as the default router gateway address) can be a proxy point for many destinations in the network. Other addresses, such as the broadcast address, “.255”, the network address itself, “.0”, or other similar proxy points also can be used. 
     Other means of point identification involve common network infrastructure elements, such as DNS servers or gateway routers. For example, when a DNS request is issued from a client it is sent from the client&#39;s local DNS server. Measuring the performance to this DNS server can be used as a proxy for the destination performance. When multiple clients share a DNS server (as is common) this measurement can be used as a proxy for all those clients. When a DNS request is observed locally, some active measurements (i.e. active probes, pings, etc.) can be made to the originating DNS server. The path that represents the best performance (or lowest link utilization) to the DNS server can be used for the upcoming transaction. To enable subsequent decisions, the Time To Live (TTL) of the response should be set low. This allows subsequent responses that may differ due to dynamic changes in network performance or link load. 
     The use of DNS servers is a common technique for global load balancing. However, in order to use DNS servers for more explicit routing, the client address space needs to be mapped to the DNS server. In addition, the use of DNS servers to identify proxy points assumes proximity of the client and the DNS server. 
     Another approach to identifying proxy points is to use third-party measurements from a variety of locations throughout the network to identify common points representing a set of destinations. This approach commonly involves triangulation of third-party measurements to a set of destinations, e.g. an entire Autonomous System, to identify common proxy points for those destinations. Once identified, the proxy points can be communicated to the edge device making the measurements for routing and other purposes. In this case, the performance measurements from the third-party servers are accurate, but an assumption is made that the topology view from the third-party servers closely matches that of the source, at least close to the destinations. Thus, an extensive array of third-party measurements may be needed for this approach to be effective. 
     Although the present invention has been discussed with respect to specific embodiments, one of ordinary skill in the art will realize that these embodiments are merely illustrative, and not restrictive, of the invention. For example, although the above description describes route control as relating to Internet data, it should be understood that the present invention relates to networks and route control in general and need not be restricted to Internet data and signals and can be applied to the fields of communication and networks in general. The scope of the invention is to be determined solely by the appended claims. 
     In the foregoing specification, the invention is described with reference to specific embodiments thereof, but those skilled in the art will recognize that while the invention is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular applications, its usefulness is not limited thereto and it can be utilized in any number of environments and applications without departing from the broader spirit and scope thereof. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive.