Patent Publication Number: US-7212495-B2

Title: Signaling for reserving a communications path

Description:
§ 0. RELATED APPLICATIONS 
     Benefit is claimed, under 35 U.S.C. § 119(e)(1), to the filing date of provisional patent application Ser. No. 60/270,399, entitled “HARDWARE IMPLEMENTATION OF A SIGNALING PROTOCOL”, filed on Feb. 21, 2001 and listing Ramesh Karri, Malathi Veeraraghavan, Brian Douglas and Haobo Wang as the inventors, for any inventions disclosed in the manner provided by 35 U.S.C. § 112, ¶ 1. This provisional application is expressly incorporated herein by reference. However, the invention is not intended to be limited by any statements in that provisional application. Rather, that provisional application should be considered to describe exemplary embodiments of the invention. 
    
    
     § 1. BACKGROUND OF THE INVENTION 
     § 1.1 Field of the Invention 
     The present invention concerns signaling used to reserve a communications path having certain characteristics. More specifically, the present invention concerns, a high-speed, high capacity call signaling protocol. 
     § 1.2 Description of Related Art 
     The description of art in this section is not, and should not be interpreted to be, an admission that such art is prior art to the present invention. Circuit switched and packet switched networks are introduced in §1.2.1. The need for label switched paths, their operation, and their establishment is introduced in § § 1.2.2–1.2.4, respectively. Finally, the need for higher capacity, high speed call signaling is introduced § 1.2.5. 
     §1.2.1 Circuit Switched Networks and Packet Switched Networks 
     Circuit switched networks establish a connection between hosts (parties to a communication) for the duration of their communication (“call”). The public switched telephone network (“PSTN”) is an example of a circuit switched network, where parties to a call are provided with a connection for the duration of the call. Hence, circuit switched networks are said to be “connection-oriented”. Unfortunately, many communications applications, circuit switched networks use network resources inefficiently. Consider for example, the communications of short, infrequent “bursts” of data between hosts. Providing a connection for the duration of a call between such hosts simply wastes communications resources when no data is being transferred. Such inefficiencies have lead to “connectionless” packet switched networks. 
     Packet switched networks traditionally forward addressed data (referred to as “packets” in the specification below without loss of generality), typically on a best efforts basis, from a source to a destination. Many large packet switched networks are made up of interconnected nodes (referred to as “routers” in the specification below without loss of generality). The routers may be geographically distributed throughout a region and connected by links (e.g., optical fiber, copper cable, wireless transmission channels, etc.). In such a network, each router typically interfaces with (e.g., terminates) multiple links. 
     Packets traverse the network by being forwarded from router to router until they reach their destinations (as typically specified by so-called layer-3 addresses in the packet headers). Unlike switches, which establish a connection for the duration of a “call” or “session” to send data received on a given input port out on a given output port, routers determine the destination addresses of received packets and, based on these destination addresses, determine, in each case, the appropriate link on which to send them. Hence, such networks are said to be “connectionless”. Routers may use protocols to discover the topology of the network, and algorithms to determine the most efficient ways to forward packets towards a particular destination address(es). Since the network topology can change, packets destined for the same address may be routed differently. Such packets can even arrive out of sequence. 
     § 1.2.2 The Need for Label Switched Paths 
     In some cases, it may be considered desirable to establish a fixed path through at least a part of a packet switched network for at least some packets. More specifically, merely using known routing protocols (e.g., shortest path algorithms) to determine paths is becoming unacceptable in light of the ever-increasing volume of Internet traffic and the mission-critical nature of some Internet applications. Such known routing protocols can actually contribute to network congestion if they do not account for bandwidth availability and traffic characteristics when constructing routing (and forwarding) tables. 
     Traffic engineering permits network administrators to map traffic flows onto an existing physical topology. In this way, network administrators can move traffic flows away from congested shortest paths to a less congested path, or paths. Alternatively, paths can be determined autonomously, even on demand. Label-switching can be used to establish a fixed path from a head-end node (e.g., an ingress router) to a tail-end node (e.g., an egress router). The fixed path may be determined using known signaling protocols such as RSVP and LDP. Once a path is determined, each router in the path may be configured (manually, or via some signaling mechanism) to forward packets to a peer (e.g., a “downstream” or “upstream” neighbor) router in the path. Routers in the path determine that a given set of packets (e.g., a flow) are to be sent over the fixed path (as opposed to being routed individually) based on unique labels added to the packets. Analogs of label switched paths can also be used in circuit switched networks. For example, generalized MPLS (GMPLS) can be used in circuit switched networks having switches, optical cross-connects, SONET/SDH cross-connects, etc. In MPLS a label is provided, explicitly, in the data. However, in GMPLS, a label to be associated with data can be provided explicitly, in the data, or can be inferred from something external to the data, such as a port on which the data was received, or a time slot in which the data was carried, for example. 
     § 1.2.3 Operations of Label Switched Paths 
     Recognizing that the operation of forwarding a packet, based on address information, to a next hop can be thought of as two steps—partitioning the entire set of possible packets or, other data to be communicated (referred to as “packets” in the specification without loss of generality), into a set of forwarding equivalence classes (“FECs”), and mapping each FEC to a next hop. As far as the forwarding decision is concerned, different packets which get mapped to the same FEC are indistinguishable. In one technique concerning label switched paths, dubbed “multiprotocol label switching” (or “MPLS”), a particular packet is assigned to a particular FEC just once, as the packet enters the label-switched domain (part of the) network. The FEC to which the packet is assigned is encoded as a label, typically a short, fixed length value. Thus, at subsequent nodes, no further header analysis need be done—all subsequent forwarding over the label-switched domain is driven by the labels. A label-switched path is defined by the concatenation of one or more label-switched hops, allowing a packet to be forwarded from one label-switching router (LSR) to another across the MPLS domain. 
     Recall that a label may be a short, fixed-length value carried in the packet&#39;s header (or may be inferred from something external to the data such as the port number on which the data was received (e.g., in the case of optical cross-connects), or the time slot in which the data was carried (e.g., in the case of SONET/SDH cross connects) of addressed data or of a cell) to identify a forwarding equivalence class (or “FEC”). Recall further that a FEC is a set of packets (or more generally data) that are forwarded over the same path through a network, sometimes even if their ultimate destinations are different. At the ingress edge of the network, each packet is assigned an initial label (e.g., based on all or a part of its layer 3 destination address). More specifically, an ingress label-switching router interprets the destination address of an unlabeled packet, performs a longest-match routing table lookup, maps the packet to an FEC, assigns a label to the packet and forwards it to the next hop in the label-switched path. 
     In the MPLS domain, the label-switching routers (LSRs) ignore the packet&#39;s network layer header and simply forward the packet using label-swapping. More specifically, when a labeled packet arrives at a label-switching router (LSR), the input port number and the label are used as lookup keys into an MPLS forwarding table. When a match is found, the forwarding component retrieves the associated outgoing label, the outgoing interface (or port), and the next hop address from the forwarding table. The incoming label is replaced with the outgoing label and the packet is directed to the outgoing interface for transmission to the next hop in the label-switched path. 
     When the labeled packet arrives at the egress label-switching router, if the next hop is not a label-switching router, the egress label-switching router discards (“pops”) the label and forwards the packet using conventional longest-match IP forwarding. 
     § 1.2.4 Establishing Label Switched Paths 
     In the foregoing example, each label-switching router had appropriate forwarding labels. However, these labels must be provided to the label-switching routers in some way. Although labels may be manually assigned on all routers involved in the path, in which case no signaling operations by the nodes are needed, in most cases, the signaling protocols are used to set up a path and distribute labels. For example, the label distribution protocol (LDP) and the resource reservation protocol (RSVP) have been used to signal paths. Nodes using these signaling protocols basically use a FEC to bind a label with a received label, and communicate a {label,FEC} binding to a peer or neighbor node, to establish of a label-switched path. Most signaling protocols are implemented in software. However, such software implementation limits the speed at which paths can be established (or at which calls can be set up and torn down). 
     § 1.2.5 The Need for Higher Capacity, Higher Speed Call Signaling 
     Connection (or call) setup and release procedures and the associated message exchanges constitute a signaling protocol. A controller in the switch processes the signaling messages and programs the switch fabric. Setting up a connection in a connection-oriented network basically includes four steps. First, a path for the connection is determined. Routing tables created from data collected by the routing protocols may be used for determining segments or links of such a path. Second, connection admission control (CAC) may be performed. CAC procedure determines if the resources requested by the call are available, reserves these resources, and selects channel identifiers (e.g., interface numbers and time slots in Time Division Multiplexed (TDM) circuit switches; interface numbers and wavelength numbers in WDM circuit switches; interface numbers, Virtual Path Identifiers/Virtual Channel Identifiers in ATM switches; interface numbers and labels in MultiProtocol Label Switches; a combination of source and destination IP addresses, source and destination port numbers, protocol type, in IP switches). Third, switch fabrics (or forwarding information) of switches or nodes in the path are programmed. This may entail programming schedulers and creating table entries that map incoming channel identifiers to outgoing channel identifiers. Fourth, the state information of active connections is updated and connection references are managed. 
     Following data transfer, releasing the resources reserved for the connection tears down a connection. This entails deleting the connection entries from the various data tables. 
     Generally, existing signaling protocol messages are complex with many parameters. Furthermore, state information associated with individual calls can become unwieldy. Consequently, such signaling protocols have traditionally been implemented in software. The call handling capacities of such software-implemented signaling protocols is on the order of 1000–10,000 calls/sec. 
     The need to speed up call or connection signaling, and to increase the capacity of call signaling, in both packet-switched and circuit switched networks, is now introduced. 
     Given industry momentum to transport voice telephony traffic over packet-switched networks, there is an increasing need for delay guarantees for interactive sessions. Interactive voice traffic has a one-way maximum delay requirement of 150 ms for excellent quality voice and 400 ms for acceptable quality voice. These delay guarantees are difficult to provide in connectionless IP networks and is a primary driver for connection-oriented packet-switched networks. 
     Telecommunications service providers are deploying ATM networks with TDM-ATM gateways to relieve the capacity exhaust problem in their tandem switches that interconnect central offices. On-demand setup and release of ATM virtual circuits is needed to support the large number of voice calls. Consider admitting voice calls into a Fore Systems&#39; ASX-4000 ATM switch which has a 40 Gbps switch fabric and which supports a maximum of 224 ports. In the worst case, when all virtual circuits are for voice calls that use of 32 Kbps voice coding, 1.25M (=40 Gbps/32 Kbps) calls can be held simultaneously. The mean holding time of voice calls has been measured to be 3 minutes. To keep the switch interfaces fully loaded, the signaling protocol processor should handle 1.25M/180 sec=7000 calls/sec. If 8 Kbps voice coding is used, then this number increases to 28000 calls/sec. This example illustrates the need for scalable, high-capacity, call/connection signaling protocols. 
     In practice, all flows are not voice calls, and hence arguably, the call handling capacities of switches need not be as high as projected. However, telephony voice is just one form of interactive communication. Supporting human-to-computer and computer-to-computer interactive communications on connection-oriented networks will require scaling of call handling capacities. The delay needs of human-to-computer interactive applications such as telnet and web accesses have been studied. For the telnet application, a delay of 200 ms has been reported. Empirical data also shows that only 10 KB are exchanged per flow on average. A 1 Tb/s switch could handle 100M of such flows/sec in the limit. The inventors believe that a software implementation of RSVP cannot support flow-based QoS control of such a large number of flows. 
     Some believe that a trend back to circuit switching will occur because they assume that bandwidth will soon become a commodity. Very large WDM switch fabrics and support for large number of wavelengths per fiber confirm this trend. If bandwidth becomes a commodity, sending data in packets to exploit silences in bursty traffic will become unimportant. Instead a lightpath can be set up end-to-end in an all-optical bit-rate-transparent WDM network. The ability to set up and release lightpaths on demand to allow for sharing of resources at the call level is the technology that would enable this. 
     Switched lightpaths (i.e., lightpaths set up and released on-demand) have already been proposed. Bandwidth trading services allow customers to trade bandwidth for wire service on a daily and even hourly basis. Optical Networks has proposed dynamic management of lightpaths in its Optical Link Management Protocol (OLMP) suite. Switched lightpaths can also be used for web mirroring. If holding times of lightpaths are long (as in leased lines) or if the number of lightpaths needed are small (as in initial web mirroring deployments), the call handling capacities of WDM switches could be managed by implementing signaling protocols in software. However, in the near future the present inventors believe that bandwidth trading will occur on a per-second basis and that the use of personal web site mirrors will become widespread. To support these emerging applications, call-handling capacities of WDM switches should be at least an order of magnitude higher than that afforded by software implemented signaling protocols. 
     WDM lightpaths are ideal for large end-to-end bulk-data transfers. In 1975, Miyahara and Schwartz showed that for large file transfers, at comparable data rates, circuit-switched networks outperform packet-switched networks from both a delay and throughput point of view. Since there is no burstiness involved in such bulk transfers of stored files from one computer to another, high-bandwidth WDM lightpaths can be set up on demand and released after downloading the file (the application data is transported directly on the WDM layer without TCP/IP). This implies that given the large number of end hosts, large call handling capacities could indeed be needed. Consider using a 1152×1152 Xros optical switch. Assuming that 10 MB files are transferred at 10 Gb/s in the worst case and assuming that end hosts can keep up with data arriving at this rate, a call handling capacity of (1152×(10×8))×10 ms=14400 calls/sec is required. 
     Fore Systems&#39; ASX-4000 switch supports  1200  calls/sec and about 100,000 connections. In Tb/s switch fabrics these numbers will increase by another two orders of magnitude. YESSIR can support 1550 voice over IP calls/sec. An OC-3 connection can support 2400 64 Kb/s voice calls. Hence, in the worst case a Tb/s IP router should support over 15 million simultaneous calls (when all IP flows are voice calls). 
     Toward building large-scale switches, the current industry focus is on increasing packet handling capacities of switch fabrics from Gb/s to Tb/s. Although an increase in packet handling capacities and line card data rates requires a corresponding increase in call handling capacities of switches, this problem has received little attention. This is because most of the work on scalability of packet switch fabrics has targeted connectionless internet protocol (IP) routers, while call handling arises only in connection-oriented networks. However, in the last few years, resource reservation to support Quality-of-Service (QoS) guaranteed flows has gained attention. Internet Engineering Task Force (IETF) is addressing this issue by augmenting IP routers with connection-oriented capabilities. 
     QoS control solutions such as Integrated Services (Intserv) and Differentiated Services (Diffserv) are being developed and evaluated based on the premise that call handling capacities do not scale with packet handling capacities of switch fabrics. This assumption has also relegated circuit-switched networks, including high-speed Wavelength Division Multiplexed (WDM) networks, to just serve as wires. 
     As can be appreciated from the foregoing examples and trends, the time for call or connection signaling should be decreased, and the capacity of call signaling should be increased. This is particularly true given the increasing capacity, both in terms of number of calls that can be services and connection throughput, of switches and routers. 
     § 2. SUMMARY OF THE INVENTION 
     The present invention provides a call signaling protocol that uses simplified messaging and novel data structures. Messages may include messages to set up, confirm set up, tear down, and confirm tear down of a connection. 
     The available capacity of communications links may be tracked so that it can be quickly determined whether or not a link can handle a call. 
     Segments (e.g., time slots, wavelengths, etc.) of a link having enough available capacity may be allocated by a separate operation. Connection state information is also tracked. 
     The signaling protocol can be implemented in hardware. Such an implementation enables high-speed, high-capacity, call signaling. 
    
    
     
       § 3. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an communications network in which the present invention may operate. 
         FIG. 2  illustrates an exemplary node of the present invention. 
         FIG. 3  illustrates an exemplary switch fabric that may be managed by the present invention. 
         FIG. 4  illustrates an exemplary setup message that may be used by a call signaling method of the present invention. 
         FIG. 5  illustrates an exemplary setup success message that may be used by a call signaling method of the present invention. 
         FIG. 6  illustrates an exemplary release or release confirm message that may be used by a call signaling method of the present invention. 
         FIG. 7  is a state machine illustrating exemplary setup and release functions that may be used by a call signaling method of the present invention. 
         FIG. 8  is a state diagram illustrating the different states of a connection. 
         FIG. 9  illustrates an exemplary switch mapping table that may be managed by a call switching method of the present invention. 
         FIG. 10  illustrates an exemplary state table that may be managed by a call switching method of the present invention. 
         FIG. 11  illustrates an exemplary connectivity table that may be managed by a call switching method of the present invention. 
         FIG. 12  illustrates an exemplary routing table that may be used by the present invention. 
         FIG. 13  illustrates an exemplary connection admission control (CAC) table that may be managed by a call switching method of the present invention. 
         FIG. 14  illustrates the relationship between several exemplary tables. 
         FIG. 15  is a flow diagram of an exemplary connection setup method. 
         FIG. 16  is a flow diagram of an exemplary connection setup success method. 
         FIG. 17  is a flow diagram of an exemplary connection release method. 
         FIG. 18  is a flow diagram of an exemplary connection release confirm method. 
         FIG. 19  illustrates an exemplary segmented communication resource table that may be used by the present invention. 
         FIG. 20  is a flow diagram of an exemplary segmented communication resource method. 
         FIG. 21  illustrates an exemplary connection reference number table that may be used by the present invention. 
         FIG. 22  is a flow diagram of an exemplary segmented connection reference number method. 
         FIG. 23  illustrates an exemplary apparatus that may be used with the present invention. 
         FIG. 24  illustrates the architecture of a WILDFORCE reconfigurable board. 
         FIG. 25  illustrates an exemplary connectivity table implemented in an exemplary embodiment of the present invention. 
         FIG. 26  illustrates an exemplary routing table implemented in an exemplary embodiment of the present invention. 
         FIG. 27  illustrates an exemplary CAC table implemented in an exemplary embodiment of the present invention. 
         FIG. 28  illustrates an exemplary state table implemented in an exemplary embodiment of the present invention. 
         FIG. 29  illustrates an exemplary switch mapping table implemented in an exemplary embodiment of the present invention. 
         FIG. 30  illustrates different control signals to access memory. 
         FIGS. 31 and 32  illustrate different states of a processor and a memory interface. 
         FIGS. 33–36  illustrate timing diagrams for an exemplary embodiment of the signaling protocol of the present invention implemented in hardware. 
         FIG. 37  is a table summarizing the results of the timing diagrams of  FIGS. 33–36 . 
     
    
    
     § 4. DETAILED DESCRIPTION 
     The present invention involves methods, apparatus and data structures for providing a high-speed, high capacity signaling protocol. The following description is presented to enable one skilled in the art to make and use the invention, and is provided in the context of particular applications and their requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles set forth below may be applied to other embodiments and applications. Thus, the present invention is not intended to be limited to the embodiments shown and the inventors regards their invention as the following disclosed methods, apparatus and data structures and any other patentable subject matter. 
     In the following, an exemplary environment in which the present invention may operate is described in § 4.1. Then, high-level operations and states of the present invention are described in § 4.2. Thereafter, exemplary methods, data structures and apparatus that may be used to effect those operations are described in § 4.3. Examples illustrating operations preformed by exemplary embodiments of the invention are then provided in § 4.4. The results of a simulation performed on the exemplary embodiment are described in § 4.5. Finally, some conclusions regarding the present invention are set forth in § 4.6. 
     § 4.1 Environment in Which the Present Invention May Operate 
     The present invention may be used in communication networks including nodes for forwarding addressed data, such as packets. The present invention may be used to configure such nodes for potential dedicated connections between two host devices. 
       FIG. 1  includes an exemplary communications network (or transport network)  100  in which the present invention may operate. The network  100  includes an ingress node  105  coupled with a first device (e.g., a source device or call initiating device)  102 , an egress node  110  coupled with a second device (e.g., a destination device or a called device)  112 , and a connection  115 . This connection  115  may be part of a circuit-switched network or a connection-oriented packet-switched network, and may be formed by at least one intermediate node, or by a link between the nodes  105  and  110 . 
       FIG. 2  is an exemplary node, e.g., a label-switching router (LSR)  200  in which the present invention may be used. The router  200  may include a logical data plane  205  and a logical control plane  210 . The data plane includes forwarding operation(s)  278 , forwarding information  276 , IN ports  215 ,  220  and OUT ports  225 ,  230 . These ports may serve to terminate communications links (not shown). The forwarding operation(s)  278  may forward data received on the IN ports  215 ,  220 . Based on the forwarding information  276 , which may include IN ports, IN labels, OUT ports and OUT labels in a packet-switched network, destination information in the received data, or communications resource identifier in a circuit-switched network, the router  200  transmits the data through the appropriate OUT port  225 ,  230 . 
     The control plane  210  may include routing information  265 , temporary storage  260 , connectivity information  270 , call state information  280 , connection admission control (CAC) information  285 , switch mapping information  290 , segmented communications resource (e.g., a multiplexed link such as a TDM link, a WDM link, etc.) operation(s)  297 , segmented communications resource information  296 , connection identification (e.g., reference number) operation(s)  287 , connection identification (e.g., reference number) information  289  and signaling operations  235 . 
     Routing information  265  is used by a signaling protocol to form a part of a connection. The routing information  265  includes information that may be used to determine through which port a particular destination can be reached. Temporary storage  260  may be used to store data for functions performed by signaling operations  235 . Connectivity information  270  correlates a connection identifier from a directly upstream node in a connection to a corresponding connection identifier in a present node. State information  280  includes information about the state of a connection. CAC information  285  is referenced to determine available bandwidth on a link that can be used as a part of a connection to a given destination address. Switch mapping information  290  is used to program the forwarding information  276  of the data plane. Switch mapping information  290  may be used to correlate incoming and outgoing interface identifiers and communications resource identifiers, so that the forwarding operation(s)  278  can forward incoming data to corresponding OUT ports. 
     Segmented communications resource operation(s)  297  allocates the communication resources of the router  200 . Communication resource availability is stored in segmented communications resource information  295 . Connection identifier (e.g., reference number) operation(s)  287  assigns a local identifier (e.g., reference number) to each of the different connections being handled by the router  200 . Reference number availability information is stored in connection identifier (e.g., reference number information  289 . 
     Signaling operations  235  include connection set up operation(s)  240 , connection set up success operation(s)  245 , connection release operation(s)  250  and connection release confirm operation(s)  255 . The connection set up operation(s)  240  establishes a connection to the next node in path that leads to a destination. That is, it  240  finds a path from the present node to the next node and allocates the necessary bandwidth between the nodes. The next node executes the same operation  240 , and so on, until the destination node is reached and the call is coupled to the called device. The connection set up success operation(s)  245  confirms the establishment (or failure) of a connection. The release operation(s)  250  and the release confirm operation(s)  255 , are used to release any allocated bandwidth once a connection is torn down. These operation(s)  250 ,  255  are also used in the event of an error in connection set up operation. Further interactions between these operations as it pertains to the present invention will be described below. 
     More specifically, the signaling operation  235  may be effected by a signaling protocol processing engine may be part of a switch fabric board. An exemplary switch fabric board  300  is shown in  FIG. 3 . The switch fabric board  300  includes de-multiplexers  305 , a space switch  310  and multiplexers  315 . Signals on the incoming interfaces to the switch fabric are de-multiplexed to the space switch&#39;s cross connect rate. The input and output ports to the space switch  310  are uniquely identified by the (interface number, time-slot number) pair. Signals on the output ports of the space switch  310  are multiplexed (e.g., up) to the (e.g., higher) rate of the output interfaces of the switch fabric for transmission to the next node. An example switch fabric is the SONET/SDH TADM device from Lucent Technologies, Inc. that supports 155, 622, and 2488 Mbits/s SONET/SDH interfaces with a cross-connect rate of STS-1 granularity between receive ports. It supports STS48/STM-16, quad STD-12/STM-4 and quad STS-3/STM-1 interface rates. 
     Switch fabric board  300  may have a generic microprocessor interface  325 . The switch fabric board  300  can be configured through the local data bus  320 , either by the microprocessor  325 , or by the signaling protocol processor  330 . The signaling protocol processor  330  may process signaling protocol messages and dynamically configure the switch fabric  300  by writing to the switch mapping table  335 , while the microprocessor  325  may perform traffic monitoring and network management by reading registers  340 ,  345 ,  350 ,  355 ,  360 . Processing signaling messages entails maintaining the state information  360  associated with each connection in the switch fabric and mandates the use of memory in the design. External RAM to maintain the state information may be used. Less frequently used and/or more complicated operations such as routing, exception and error handling tasks may be implemented in software and carried out in the background concurrent with the signaling protocol processing. More frequently used and/or less complicated operations may be performed in hardware for providing faster call handling capacities. The signaling messages may be transported over network and data link layer protocols such as IP and Ethernet. Appropriate link termination boards may be used to strip these link or network layer protocol headers before sending the signaling message to the signaling hardware for processing. 
     § 4.2 High-Level Functions, Messages and States of the Present Invention 
     High-level functions that may be performed by the present invention include establishing a connection, tearing down a connection, allocating communication resources, and allocating connection identifiers (e.g., reference numbers). The Setup and Setup-Success messages may be used by the connection establishing function of the present invention to establish a new connection. An exemplary setup message  400  is shown in  FIG. 4 , and an exemplary setup success message  500  in shown in  FIG. 5 . Release and Release-confirm messages may be used by the connection tearing function of the invention to release a previously established connection. Exemplary Release and Release-confirm messages  600  are shown in  FIG. 6 . 
     The setup message  400  includes information that is used to create a connection for a device coupled to an ingress node. It is an exemplary embodiment used in a TDM network. The exemplary setup message  400  includes a field identifying the message length, the time to live (TTL), the message type, the connection reference of the previous node, the destination IP address, the source IP address, the previous node&#39;s IP address, the minimum requested bandwidth, the maximum requested bandwidth, the interface number, a segmented communications resource identifier (e.g., a time-slot number), pad bits and a checksum. 
     The fields of the exemplary setup success message  500  include the message length, the bandwidth allocated, the message type, the connection reference number of the sender, the connection reference number of the current node, pad bits, and a checksum. 
     The fields of the exemplary release and release confirm messages  600  include the message length, the cause of the release, the message type, the connection reference number of the sender, the connection reference number of the current node, pad bits, and a checksum. 
     The state machine  700  shown in  FIG. 7  illustrates a high level diagram describing the steps of the setup and release functions perform by the invention. The state machine reflects core functions that may be performed by an exemplary signaling protocol: memory reads and writes. For simplicity, those states during which the protocol either waits for memory or writes data to the outgoing messages registers are not shown in the state machine. 
     A connection may be in one of four states.  FIG. 8  is a state diagram illustrating these four different states, and the messages that change the state of the connection. These four states are closed  805 , setup sent  810 , established  815 , and release sent  820 . 
     When a connection does not exists it is in the closed state  805 . While setup messages are being transmitted  830  to couple a source device and a destination device, the connection is in the setup sent state  810 . If an error occurs and a release or release confirm message is received  835  , the connection goes to a release sent state  820 . If a setup success message is received  845  , the connection is in an established state  815 . Once a release message is received  840  , the connection goes to a release sent state. Finally, when a release confirm is received  825  , the connection returns to a closed state  805 . 
     The states of the nodes that make up the connection include a normal state, when no errors are occurring and the signaling protocols is functioning in a normal manner, and an error state, when an error occurs during an operation of a signaling protocol. 
     With reference to the exemplary embodiment of  FIG. 3 , a set up function of the invention is now described. Setting up a new connection includes Setup message and Setup-Success message processing. Setup message processing begins with finding the address, from the routing table  345 , of a next link (on the connection to the destination at the requested data rate) and an outgoing interface terminating that link. This information is used as an index into the connection admission control (CAC) table  355  to determine if the bandwidth available on the interface can support the call. These connection admission control steps (rd_route→rd_CAC in the state machine) are repeated until an outgoing interface on a path to the destination device with sufficient bandwidth is found. Once an outgoing interface with sufficient bandwidth is found, the available bandwidth associated with that interface is updated in the CAC table  355  (wr cac state) to reflect admission of the call and a locally generated connection identifier (e.g., reference number) is associated with this connection (rd cxn rf state). On the other hand, if an interface with a sufficient bandwidth is not found, an error code is set and the machine transitions into the error state. 
     Following connection admission control, a set up message is generated as follows and sent to the next node. While most of the entries in the incoming setup message are directly copied into the outgoing message, only the connection reference and IP address entries associated with the node receiving this message are modified. The address of the next node, outgoing interface number to which it is connected, connection identifier (e.g., reference number) of the message sender and the maximum bandwidth are stored in a scratch register. The requested bandwidth is allocated on the outgoing interface by allocating as many time-slots as are necessary (one at a time) and the switch is programmed by writing the outgoing interface/time-slot pairs into the switch mapping table  335  (rd ts→wr switch). These pairs are also written into the outgoing message. The state information is saved into the state table  360  using the connection reference number as the index with the state of the connection set to setup sent. Finally, the outgoing message is transmitted. 
     Processing the setup-success message  500  begins with indexing into the state table  360  using the connection reference number in the message. Then the state of the connection is changed from setup sent to established. At the same time, the setup success message is updated using the connection identifier (e.g., reference number) from the state table and sent. If, on the other hand, the state of the state table entry is not setup sent, an error code is set and the machine transitions into the error state. The release and release confirm messages are similarly processed as shown in the state machine and will be discussed below. 
     The segmented communications resource (e.g., a time-slot on a TDM link, a wavelength on a WDM link, etc.) allocating function of the invention allocates the bandwidth of the switch fabric to the connections that use the router. For example in a TDM network time-slots are allocated and in a WDM network, wavelengths are allocated. When a connection is set up at a router, the router identifies the connection by giving it an identifier (e.g., a reference number). Therefore, the present invention includes a connection identifier (e.g., reference number) allocating function. 
     § 4.3 Exemplary Data Structures, Methods and Apparatus 
     Exemplary methods and data structures for effecting the functions summarized in § 4.2 are described in this section. More specifically, § 4.3.1 describes exemplary data structures, § 4.3.2 describes exemplary connection setup operations, § 4.3.3 describes an exemplary connection setup success operations, § 4.3.4 describes exemplary connection release operations, § 4.3.5 describes exemplary connection release confirm operations, § 4.3.6 describes exemplary segmented communication resource operations and § 4.3.7 describes exemplary connection identifier (e.g., reference number) operations. Then, exemplary apparatus that may be used to effect the functions summarized in § 4.2 are described in § 4.3.8. 
     § 4.3.1 Exemplary Data Structures 
     One embodiment of the signaling protocol of the present invention maintains and/or uses five data structures. These data structures include, a switch mapping table, a state table, a connectivity table, a routing table, and a CAC table. Exemplary data tables are shown in  FIGS. 9 ,  10 ,  11 ,  12 , and  13 , respectively. The exemplary switch-mapping table  900  is used to configure the input-output paths of the switch. Configuring a switch may be effected by modifying the contents of this table. The state of each active connection is maintained in the state table  1000 . The connectivity table  1100 , the routing table  1200  and the CAC table  1300  maintain information used to allocate resources and determines next links of connections. 
     The exemplary switch-mapping table  900  includes information used to program the switch once the connection has been established. The table  900  maps incoming channel identifiers (e.g., time-slot/interface pairs) to outgoing channel identifiers (e.g., time-slot/interface pairs). The index into the exemplary switch-mapping table  900  may be 20-bits wide and may be obtained by concatenating the 12-bit connection identifier (e.g., reference number) chosen during call setup with an 8-bit offset associated with an amount of bandwidth allocated for the connection. For example, an OC12 connection through a switch with an OC-1 cross connect rate will have 12 entries in the switch mapping table. 
     The state table  1000  tracks active connections through a switch. The connection reference number in the table is used to index entries in the state table  1000  at a switch. The state table  1000  maintains the state of the connection, the bandwidth allocated for the connection, and the connection reference numbers and IP addresses of the adjacent upstream (previous) and the adjacent downstream (next) node. As mentioned above, a connection can be in one of many states. The state information about a connection is used to determine the messages that are created and sent in response to receiving a setup success message. In addition, the state table  1000  maintains a pointer into the corresponding entry in the switch-mapping table  900 . Overall, each state table entry is, e.g., 112-bits wide. 
     The interface numbers delivered in a setup message (Recall, e.g., 400.) specify outgoing interfaces on the previous switch, but the incoming interface numbers are necessary for programming the local switch. For this purpose, each switch has a connectivity table  1100  that maps the outgoing interfaces of the upstream (previous) switch into the incoming interfaces of the local switch. In one embodiment it may be assumed that one outgoing interface on the upstream (previous) switch is connected to one incoming interface of the current switch. In other embodiments, each connection may be associated with multiple interfaces. The index to entries in the connectivity table  1100  is, e.g., 40-bits wide, and is obtained by appending the 8-bit interface number received in the setup message to the end of the 32-bit IP address of the node that sent the message. Information contained in the connectivity table is assembled by the host system and may not be modified by the signaling protocol. 
     Calls are routed based on destination IP addresses contained in setup messages and the bandwidth requested by the call. Optional next-hop addresses (or alternatively, outgoing links and ports) are maintained for each destination in the routing table  1200 . If a first of the optional addresses is associated with a link that does not have sufficient bandwidth to support the call, then the next optional address is tried. The routing table  1200  returns a 32-bit IP address to the next-hop node that can support a connection to the destination address. Once again, the entries of the routing table are maintained by the host system. With a 42-bit address, the routing table  1200  has the largest address space of any table at the node. The next node address is written into the state table  1000  after the routing table lookup. 
     Connection admission is determined by the availability of bandwidth on a particular interface. The connection admission control (CAC) table  1300  holds the interface number, total bandwidth and the available bandwidth associated with the next-hop. Separating the CAC table  1300  from the routing table  1200  simplifies updating the bandwidth information. 
     The relationships between some of the tables used by the protocol are shown in  FIG. 14 . Arrow  1405  shows how the next hop IP address field  1405 ″ of the state table  1420  is populated by the next hop field  1405 ′ of the routing table  1425 . Arrow  1408  represents the information in the next hop address field  1405 ′ also being used to index the CAC table  1435 . From the CAC table  1435  an OUT interface  1410 ′ is determined and, as represented by arrow  1415 , bandwidth is reserved by decrementing the available bandwidth for that particular IP address. Arrow  1410  represents the outgoing interface field  1410 ″ of the switch mapping table  1430  being populated by the out interface information  1410 ′ in the CAC table  1435 . 
     § 4.3.2 Exemplary Connection Setup Operations 
       FIG. 15  is a flow diagram of an exemplary method  240 ′ that may be used to effect various connection setup operations  240 . The exemplary connection setup method  240 ′ of  FIG. 15  starts at block  1504 . In trigger event block  1508  one of three events may occur. First, if a setup message is received from an upstream (previous) node. Then the method  240 ′ proceeds to block  1512 , where routing information  265  is used to determine the next node in the potential connection. 
     Then the method  240 ′ proceeds to decision block  1516 . If the routing information  265  includes an appropriate next node address, the method  2401  proceeds to block  1524 , but if the routing information does not include an appropriate next node address, the method proceeds to block  1520 . In block  1520 , an error occurrence is indicated and recovery operations are initiated. Due to the complexity of at least some recovery operations, some recovery operations are performed in software, and may include executing a routing program to determine the next node address for the connection. Then the method  240 ′ is left via return node  1560 . 
     Referring back to decision block  1516 , assuming a suitable next node address is determined, method  240 ′ proceeds to block  1524 , where the amount of bandwidth available for the next node address is determined using the CAC table  285 . Then the method  240 ′ proceeds to decision block  1528  where it is determined whether or not the available bandwidth for the next node address satisfies the requirements of the connection. If the bandwidth requirements of the connection cannot be met, the method  240 ′ returns to step  1512 , where another next node address is determined. Referring, again to block  1528 , when if a next node address with the required bandwidth is found, the method  240 ′ proceeds to block  1532 . 
     At block  1532 , the CAC table  285  is updated to reflect bandwidth allocated to the connection. (e.g., to decrease the capacity of the link). Then the method  240 ′ proceeds to block  1536 , where a connection identifier (reference number) allocation request is transmitted. Then method  240 ′ proceeds to return node  1560  where it waits for a connection identifier (reference number). 
     The connection reference number operation(s)  287  receives the request and generates returns a connection identifier (reference number). Returning to trigger event block  1508 , when a connection reference number is received by the connection setup method  240 ′, processing proceeds to block  1540 . At block  1540 , an interface number and an allocation control signal are transmitted to the segmented communications resource operation  297 . Then method  240 ′ proceeds to return node  1560  where it waits for allocated bandwidth information from that operation  297 . 
     Once again returning to trigger event block  1508 , if allocated bandwidth information is received, the method  240 ′ proceeds to block  1544 , where the connection identifier, bandwidth allocation, incoming channel identifier, and outgoing channel identifier fields of the switch mapping information  290  are updated with the acquired information. In block  1548  the local connection identifier, upstream connection identifier, state, upstream node address, down stream node address and a pointer to switch mapping table fields of the state information  280  are updated. 
     Then the method  420 ′ proceeds to block  1552 , where a setup message for the next node is generated. In block  1556 , the generated set up message is transmitted through the forwarding operation  278  to the determined next node. If the present node is the destination node, the blocks  1552  and  1556  are not performed. Then, the method  240 ′ is left via return node  1560 . 
     § 4.3.3 Exemplary Connection Setup Success Operations 
       FIG. 16  is a flow diagram of an exemplary method  245 ′ that may be used to effect various connection setup success operations  245 . The exemplary connection setup success method  245 ′ of  FIG. 16  starts at block  1604  and proceeds to trigger event block  1608 . If the method  245 ′ receives a connection setup success message from a downstream node in a potential connection, then the method  245 ′ proceeds from block  1608  to block  1612 . At block  1612  the switch mapping information  290 , stored in the control plane of the present node, is written to the forwarding information  276  in the data plane of the node. Then, the method  245 ′ proceeds to block  1616 , where the state information  280  is updated to an “established” state. 
     Then the method  245 ′ proceeds to block  1620  where a set up success message is generated and transmitted to a upstream (previous) node on the potential connection. If the node receiving the setup success message is the source node, block  1620  is not performed, and the potential connection becomes a connection. Then the method  245 ′ is left via return node  1624 . 
     A setup success operation  245  is started at the egress node of a connection. Setup success messages travel upstream through the connection, and when the ingress node receives a setup success message the connection is established and data may begin to transmit. 
     § 4.3.4 Exemplary Connection Release Operations 
       FIG. 17  is a flow diagram of an exemplary method  250 ′ that may be used to effect various connection release operations  250 . The exemplary connection release method  250 ′ of  FIG. 17  starts at block  1704 . Then, the method  250 ′ proceeds to trigger event block  1708 . When a node that is part of a connection receives a connection release message, the method  250 ′ proceeds to block  1712 . In block  1712 , using information (e.g., the connection reference number) received in the received connection release message and the state information  280 , the next node address is determined. Using the next node address, the present node finds corresponding bandwidth information in the CAC information  285 . Then the method  250 ′, at block  1716 , updates the CAC information  285  to indicate the release of bandwidth that was reserved by the connection being released. 
     From block  1716 , the method  250 ′ proceeds to block  1720 , where an interface number, a segmented communications resource identifier and a deallocate control signal are sent to the segmented communications resource operation(s)  297 . At the segmented communications resource operation(s)  297 , the bandwidth reserved for the connection is released. Then, the method  250 ′, proceeds to block  1724 , where a connection release message for/to the next node in the connection is generated and transmitted. In block  1728 , a connection release confirm message for/to the previous node, i.e., the node that sent the connection release message, in the connection is generated and transmitted. Then, the method  250 ′ is left via return node  1732 . 
     § 4.3.5 Exemplary Connection Release Confirm Operations 
       FIG. 18  is a flow diagram of an exemplary method  255 ′ that may be used to effect various connection release confirm operations  255 . The exemplary connection release confirm method  255 ′ of  FIG. 18  starts at block  1804 . At trigger event determination block  1808 , a node that is part of a connection may receive a connection release confirm message. If this message is received, the method  255 ′ proceeds to decision block  1810 , where the state of the connection is determined. 
     If the connection is in a release sent state, the method  255 ′ proceeds to block  1836 . At this point the present node has already performed the connection release method  250 ′, and any reserved bandwidth has already been released. At block  1836 , the present node transmits a connection identifier (reference number) deallocation request to the connection identifier (reference number) operation  287 . The connection identifier (reference number) operation  287  will set the provided connection reference number as available so it may be used by another connection. Then, the method  255 ′ is left via return node  1832 . 
     Referring again to decision block  1810 , if the present node is in a setup sent state, the method  2551  proceeds to block  1812 . This event occurs when a next node in a potential connection encounters an error (e.g., the next node cannot guarantee the requested bandwidth for the connection). If a next node encounters an error, it transmits a connection release confirm message to the sourcing node, which is in a setup sent state. 
     At block  1812 , the present node proceeds to tear down the potential connection. It uses information received in the message (e.g., the connection identifier (reference number)) and the state information  280 , to determine the next node address. Using the next node address the present node finds corresponding bandwidth information in the CAC information  285 . Then the method  2551 , at block  1816 , updates the CAC information  285  to indicate the release of reserved bandwidth. 
     From block  1816 , the method  2551  proceeds to block  1820 , where an interface number, a segmented communications resource identifier and a deallocate control signal are transmitted to the segmented communications resource operation(s)  297 . At the segmented communications resource operation(s)  297 , the bandwidth reserved for the connection is released. Then, the method  255 ′, proceeds to block  1824 , where generation and transmission of a connection release message for/to the upstream (previous) node in the connection occurs. Then, the method  255 ′ is left via return node  1832 . 
     § 4.3.6 Exemplary Segmented Communication Resource Operations 
     The bandwidth of a connection and the cross connect rate of the switch fabric determine the total number of segmented communications resource segments (e.g., time-slots) that are assigned to the connection. A hardware-based implementation for managing the time-slots on a switch interface is described. Time-slot availability is stored at segmented communications resource information  295  (e.g., in a table). An exemplary time-slot table  1900  is shown in  FIG. 19 . The time-slot table  1900  at a switch has as many entries as there are interfaces (e.g., ports) on the switch. Each entry is a bit-vector with the bit-position determining the time-slot number and the bit-value determining availability (‘0’) or use (‘1’) of the time-slot. In one exemplary embodiment, table  1900 , which may be stored in RAM, is implemented with an integrated priority decoder  1902 . The priority decoder determines takes a bit vector as input and determines the next available time-slot in the bit vector. An 8-bit (outgoing) interface number is the index into the time-slot table  1900 . 
     The exemplary time-slot table  1900  may return the next available time-slot on that interface as follows. When an interface number and allocate control signal are provided by the signaling state machine, the bit-vector associated with the interface number is sent into the priority decoder and the first available time-slot is returned as the next available time-slot. Then, the bit associated with the timeslot is marked as unavailable (i.e. changed from 0→1) and the updated bit-vector is written back to the table. Deallocating a timeslot follows a similar pattern. When an interface number, a time-slot and a deallocate control signal are provided to the timeslot table  1900 , the corresponding bit-vector is obtained, the bit position associated with the time-slot is modified (i.e. changed from 1→0) and the updated bit-vector is written back. For a 256×256 switch fabric with an OC1 crossconnect supporting a maximum bandwidth of OC192 per interface, the time-slot table will have 256, 192-bit entries. 
     An exemplary segmented communications resource method  297 ′ that may be used to effect segmented communications resource operation(s)  297  is illustrated in  FIG. 20 . The method  297 ′ starts at block  2004 . Then the method  297 ′ proceeds to trigger event block  2008 . If an interface (e.g., a port) number and a control signal is received and if the received control signal is an allocate control signal, the method  297 ′ proceeds to block  2012 , where a bit-vector associated with the interface number is determined. Referring to exemplary time-slot table  1900 , the bit-vectors are the rows. The method  297 ′ proceeds to block  2016 , where the first available segmented communication resource is determined (e.g., using the priority decoder  1902 ). Then method  297 ′ proceeds to block  2020 , where the bit in the bit-vector associated with the segmented communications resource (e.g., time-slot) is marked as used (or unavailable). Then the method  297 ′ is left via return block  2024 . 
     Referring back to trigger event  2008 , if a interface number, a deallocation control signal and a segmented communication resource identifier (e.g., a timeslot) is received, the method  297 ′ proceeds to block  2028 , where the bit vector associated with the received interface number is determined. Then the method  297 ′ proceeds to block  2023 , where the bit associated with the segmented communication resource is marked as available. Then the method  297 ′ is left via return node  2024 . 
     § 4.3.7 Exemplary Connection Reference Number Operations 
     A connection reference number is allocated at connection setup and deallocated during connection release. An exemplary implementation of a connection reference number generator uses a 4096-bit vector combined with a priority decoder. The priority decoder finds the first available bit (a bit position marked ‘0’), sends its index as the connection reference and updates the bit position as used (bit is marked as ‘1’). A problem with this approach is that a connection reference that is freed may be immediately assigned to a new connection. This should be avoided because messages carrying connection references of those connections whose state is marked as closed will still circulate in the IP network for an unknown period of time. Thus, errors could result in message processing due to looped messages that cause faults in current data transmissions. 
     Another exemplary connection reference number method that may be used to effect connection reference number operation(s)  287 , is a counter-based approach that generates an address into a 4096-entry table each entry of which is 1-bit wide. If the entry pointed to by the counter is available (‘0’), then it is changed to busy (‘1’) and the counter value is taken as the connection reference number. This connection reference number method can operate concurrently with the state machine speeding up the time to generate a new connection reference number. The counter is incremented at each clock until an unused connection reference number is encountered. However, this approach is essentially a linear search through  4096  (connection references are 12-bits wide) entries in the table in the worst case. 
     Therefore, approaches in the previous methods may be combined and improved in a hardware implementation. Parallel processing may be utilized by partitioning the, e.g.,  4096 , element connection reference number table  2100  into 16, 256-element tables each with its own counter. An exemplary table  2100  is shown in  FIG. 21 . This parallel structure yields 16 parallel connection references. Any time one of these is used by the signaling state machine, the corresponding module is triggered to generate a new connection reference. The hardware implementation for each connection reference generator is identical except that each of them has a different connection reference offset added. When a connection reference is freed, the 4 leading bits are used to identify one of the 16 rows in the table and the remaining bits are used to identify the entry in the row. This table entry is then set to available (i.e. changed from 1→0). An additional counter tracks the total number of connection reference numbers available. When a connection reference number is allocated the available connection references count is decremented and when a connection reference is freed the available connection references count is incremented. An additional counter may be used so that the connection references are uniformly distributed across all 16 tables. Every time a connection reference is allocated, the table count is incremented. 
     An exemplary connection reference number method  287 ′ that may be used to effect connection reference number operation(s)  287  is illustrated in  FIG. 22 . The method  287 ′ starts in node  2204  and proceeds to trigger event  2208 , where one of two event may occur. 
     If an allocation request is received, the method  2871  proceeds to block  2212 . At block  2212 , a number N, (e.g., 16), separate priority decoders  2102  are used to determine the first available second piece of a connection reference number, if any, in its respective row. Then the method  287 ′ proceeds to block  2216 , where a value from a first counter is determined. The values of the counter correspond to the N rows. Then the method  287 ′ proceeds to decision block  2220 . At decision block  2220 , the method  287 ′ determines if a second piece of a connection reference number, taken from the chosen row, is available. If a connection reference number is not available, the method  287 ′ proceeds to block  2224 , where the first counter is incremented. Then, the method  287 ′ returns to block  2216  to determine a new row. Since each of the N rows were search in parallel, in the worst case scenario, this look up step is performed N times. 
     Returning to decision block  2220 , if a second piece of a connection reference number is available in the chosen row, the method  287 ′ proceeds to block  2228 . At block  2228 , the first counter value is used as a first piece of a connection reference number, and the first piece is concatenated with the second piece of a connection reference number to form a connection reference number. 
     The method  287 ′ proceeds from block  2228  to block  2232  where the counter, which tracks the total available connection reference numbers, is decremented by one. Then, the method  287 ′ proceeds to block  2236 , where the connection reference number is returned to the connection setup operation  240  that sent the request. Then method  287 ′ is left via return node  2240 . 
     Returning to trigger event block  2208 , if a deallocation request and a connection reference number is received, the method  287 ′ proceeds to block  2244 . At block  2244 , the first piece of the connection reference number is used to locate the row in connection reference number table  2100 . Then the method  287 ′ proceeds to block  2248  where the second piece of the connection reference number is set as available in the table  2100 . Finally, in block  2252 , the counter, which tracks of total available connection reference numbers, is incremented. Then, the method  287 ′ is left via return node  2240 . 
     § 4.3.8 Exemplary Apparatus 
       FIG. 23  is high-level block diagram of a machine  2300  which may effect one or more of the operations discussed above. The machine  2300  basically includes a processor(s)  2310 , an input/output interface unit(s)  2330 , a storage device(s)  2320 , and a system bus(es) and/or a network(s)  2340  for facilitating the communication of information among the coupled elements. An input device(s)  2332  and an output device(s)  2334  may be coupled with the input/output interface(s)  2330 . Operations of the present invention may be effected by the processor(s)  2310  executing instructions. The instructions may be stored in the storage device(s)  2320  and/or received via the input/output interface(s)  23230 . The instructions may be functionally grouped into processing modules. 
     The machine  2300  may be a switch fabric including a signal control processor for example. In an exemplary router, the processor(s)  2310  may include a microprocessor, a network processor, and/or (e.g., custom) integrated circuit(s). In a preferred embodiment of the invention, at least some of the processors (e.g., a signal control processor  330 ) may be field programmable gate arrays (FPGAs). In the exemplary router, the storage device(s)  2320  may include ROM, RAM, SDRAM, SRAM, SSRAM, DRAM, flash drive(s), hard disk drive(s), and/or flash cards. At least some of these storage device(s)  2320  may include program instructions. At least a portion of the machine executable instructions may be stored (temporarily or more permanently) on the storage device(s)  2320  and/or may be received from an external source via an input interface unit  2330 . Some of the storage devices  3200  may include RAM or registers for defining, e.g., a routing table  345 , a connectivity table  350 , a CAC table  355 , and a state table  360 . Finally, in the exemplary router, the input/output interface unit(s)  2330 , input device(s)  2332  and output device(s)  2334  may include interfaces to terminate communications links. 
     Naturally, the operations of the present invention may be effected on systems other than routers. Such other systems may employ different hardware and/or software. 
     § 4.4 An Exemplary Embodiment 
     An exemplary embodiment of the signaling protocol was implemented in field programmable gate arrays (FPGAs). The re-configurable nature of FPGAs allows the addition of more features (commands or extensions) to the base subset of four commands present in the current embodiment, if desired. For this exemplary embodiment, the sizes of the various tables are reduced in order to fit the memory and the signaling protocol state machine on a single Xilinx FPGA of a multi-FPGA WILDFORCE prototype board. The WILDORCE re-configurable board architecture  2400  is shown in  FIG. 24 . It includes six FPGAs  2402 ,  2404 ,  2406 ,  2408 ,  2410 ,  2412 . Designs specified in VHDL hardware description language are synthesized and loaded into one or more of the FPGAs. A C language based library of APIs is used to configure the FPGAs with the signaling protocol, and to invoke this configured hardware signaling protocol to accelerate signaling message processing. 
     The configurable logic blocks (CLB) are the functional building block of the FPGAs. Each CLB in the Xilinx FPGAs is comprised of two four-input function generators and a pair of D-flip-flops. The largest FPGA on the WILDFORCE board has about 1200 CLBs. Simulation results have shown that this design consumes about 300 CLBs. Three FPGAs (PE 0 , PE 1  and crossbar  2402 ,  2406 ,  2404 ), two FIFOs (FIFO 0 , FIFO 1   22414 ,  2416 ) and a 128K RAM (not shown) are used to implement the signaling protocol. PE 0   2402  implements the signaling protocol state machine  700  and the state and switch mapping tables  280 ,  290 . The 128K RAM implements the routing, connectivity and CAC tables  265 ,  270 ,  285 . The signaling messages are received via FIFO 0   2414  connected to PE 0   2404  and sent out via FIFO 1   2416  connected to PE 1   2406 . A 2-bit control bus  2418  between PE 0  and PE 1  is used to carry a control signal from the signaling protocol state machine  700  to FIFO 1   2416  and a control signal from FIFO 1   2416  to the signaling protocol state machine  700 . 
     The memory requirements of the signaling protocol exceed the memory resources available on the WILDFORCE board  2400 . The routing, connectivity and CAC data  265 ,  270 ,  285  that is accessed by both the host and the signaling protocol state machine  700  may be implemented on a 128K RAM on a mezzanine card connected to PE 0   2402 . The state and switch mapping tables  280 ,  290  that are accessed by the signaling protocol state machine  700  are implemented on the PE 0   2402  FPGA. The 128K mezzanine RAM has only a 24-bit address bus. Consequently, for this exemplary embodiment, the sizes of the routing, connectivity and CAC tables  265 ,  270 ,  285  are reduced. An exemplary connectivity table  2500  is shown in  FIG. 25 , an exemplary routing table  2600  is shown in  FIG. 26  and an exemplary CAC table  2700  is shown in  FIG. 27 . Similarly, the sizes of the state and switch-mapping tables  280 ,  290  are reduced. An exemplary state table  2800  is shown in  FIG. 28  and an exemplary switch mapping table  2900  is shown in  FIG. 29 . The exemplary embodiment supports 5-bit addresses for all nodes, 16 interfaces (e.g., ports) per switch, a maximum bandwidth of 16 OC1s and a maximum of 32 connection references at each switch. 
     Memory accesses represent the majority of the actions taken by the signaling processor. A unified approach to memory is desired to reduce complexity in the processor. The signaling protocol state machine  700  accesses the tables implemented in the Mezzanine RAM or in the PE 0   2402  FPGA via a memory interface module. Therefore, implementation of the state machine  700  remains independent of the particular memory structures. 
     Generality is desired in the design of the state machine and the memory interfaces. The actions for each interface have been specified and general control signals have been developed. With slight modifications, the signaling state machine  700  can be interfaced with a wide range of memory modules. The chip select and write enable control signals are defined to support read, write, and pause actions as shown in Table 1  3000  of  FIG. 30  by the signaling state machine  700 . If the chip select signal is “0” and the write enable is “0”, a write action occurs at the memory. If the chip select signal is “0” and the write enable is “1”, a read action occurs at the memory. If the chip select signal is “1” and the write enable is “0”, a pause action occurs at the memory, and if the chip select signal is “1” and the write enable is “1”, no action occurs. 
     The signaling protocol state machine  700  uses these control signals, along with a table identifier, an address (and data when necessary) and interfaces with the specific data tables using the process shown in  FIGS. 31 and 32 . In  FIG. 31  the processor method  3100  is described. The method  3100  starts at idle node  3104  and proceeds to block  3108 . At block  3108 , if the chip select signal is “0” and the write enable is either “0” or “1”, the memory is being used. The method  3100  proceeds to block  3112 . At block  3112 , if the memory is not busy, then the method  3100  proceeds to block  3116 , where the chip select signal is a “1”. Then, the method  3100  returns to idle block  3104 . 
     The state diagram of  FIG. 32  illustrates the states of a memory interface. Beginning at node  3204 . The memory interface is at a ready state. If the chip select signal is “0” and the write enable is “0”, operation proceeds to node  3208 , and the memory interface is in a write state. After the write state is complete the memory interface proceeds to node  3212  and enters a standby state. 
     Returning to node  3204 , if the chip select signal is “0” and the write enable is “1”, operation proceeds to node  3206 , and the memory interface is in a read state. After the read state is complete the memory interface proceeds to node  3212  and enters a standby state. When the memory interface receives a chip select signal of “1”, the memory interface returns to a ready state, node  3204 . 
     § 4.5 Simulation Results 
     In almost all or all signaling protocols, SETUP message processing consumes the most time. This includes the time spent on receiving the SETUP message, time spent on SETUP message processing and the time spent on transmitting a SETUP message. An exemplary VHDL model for the signaling protocol processor was developed and then compiled, simulated and synthesized it using Synplicity design tools set for a Xilinx 4036 XLA FPGA. 
     From the timing simulation of the SETUP message shown in  FIG. 33  it can be seen that while receiving and transmitting a SETUP message (requesting a bandwidth of OC-12 at a cross-connect rate of OC-1) consumes 12 clock cycles each, SETUP message processing consumes 53 clock cycles. Overall, this translates into 77 clock cycles to receive, process and transmit a SETUP message. Processing SETUP SUCCESS ( FIG. 34 ), RELEASE ( FIG. 35 ) and RELEASE CONFIRM ( FIG. 36 ) messages consumes about 70 clock cycles total since these messages are much shorter (2 32-bit words versus 11 32-bit words for SETUP) and requires simple processing. The breakdown of the timing for each message type is shown in Table 2 of  FIG. 37 . Assuming a slow 25 Mhz clock, this translates into 3.8 microseconds for SETUP message processing and about 2.8 microseconds for SETUP SUCCESS, RELEASE and RELEASE CONFIRM message processing combined. Thus, for a complete pull-up and pull-down of a connection the total time for signal processing is around 6.6 microseconds. Compare this with the 1–2 milliseconds it may take to process signaling messages in software. Using a slightly faster clock (50 MHz) halves these processing times. FPGAs with 100 MHz clocks are already on the market and using them will decrease the processing time of the messages even further. In addition, pipelined processing of signaling messages by selective duplication of the data path to further improve the throughput may be implemented. Overall, this exemplary embodiment of a signaling protocol in FPGA hardware has demonstrated the potential for being 1,000–10,000 times faster than software implementations. 
     § 4.6 Conclusions 
     As demonstrated by the exemplary embodiment, the call handling capacities of a node may be increased by implementing a signaling protocol in hardware. Since establishing and releasing connections through a network are becoming important in both connection-oriented networks and connectionless networks emulating connection-oriented networks, the present invention solves a growing challenge. 
     The faster performance of the signaling protocol implemented in hardware decreases the overhead associated with setting up and releasing a connection. This lower overhead enables more data to be transmitted, and more calls to be handled at one time.