Method of broadcasting and multicasting using satellite medium

A method for communicating with multiple network nodes is provided in which each node of a network has a wireless link that allows data to travel to and from the nodes in parallel, thereby taking advantage of the inherent broadcast capabilities of wireless media. The wireless link may be used in parallel with a point-to-point, land-based network linking the nodes. The method may be used for multicasting or broadcasting data on a network. Specifically, the method may be used to maintain a network cache, a routing database and quality of service in a manner that is more efficient and reliable than previous methods that use serial protocols over point to point network links.

TECHNICAL FIELD

This invention relates generally to computer network communication and, more particularly, relates to a method for communicating with multiple network nodes.

BACKGROUND OF THE INVENTION

In today's computer networks, there is an increasing demand for multicasting capabilities. Multicasting is the act of sending a single data message from one node in the network to a group of other nodes. When the group includes all of the nodes in the network, the act is generally referred to as “broadcasting.” Currently, large networks such as the Internet implement multicasting by sending a message serially from one node to another, making multiple copies of the multicast data at strategic points along the way, and sending the copies down the various network paths and, eventually, to the members of the multicast group. One problem with this method is that it is inefficient, since it requires the various network nodes to expend processing power to make and transmit additional copies of the message. Another more fundamental problem is that multicasting is intended to be a parallel process—i.e. each of the recipient nodes should receive the data simultaneously—but land-based network links are inherently serial, requiring a message to be relayed from node to node before reaching its final destination. This can result in propagation delays, causing distant nodes to receive the message much later than nodes closer to the origin. Sophisticated multicast protocols have been developed to address these problems, but they consume processing overhead and only represent stopgap measures.

One specialized form of multicasting occurs in packet switched networks such as the Internet and involves the use of routers, which are a type of network node that directs data traffic between different devices on the network. When two or more computer in the network send data to one another during a communication session, routers “route” the data by determining the most appropriate paths over which the data should flow based on a number of criteria, including distance and Quality of Service (QOS). In order to make this determination, the routers have to create and maintain a routing database that describes the routing topology of the network. The routing database requires constant updating, since the routing topology can change quickly as a result of the addition, deletion, and failure of network equipment. Moment to moment changes in traffic loads at different parts of the network also need to be reflected in the routing database, since these changes can instantaneously cause previously optimal routes to become sub-optimal.

In the current approach to routing, the routers use the conventional network paths themselves to update each other with local routing data. One problem with this approach is that the very act of sending the updates impacts the data traffic on the network, and can render the updates inaccurate. Another problem relates back to the serial nature of conventional network links, in that updates transmitted by one router will reach nearby routers relatively quickly, while updates to distant routers will take much longer. As a result, a router will tend to have a good picture of the network in the local area, but a relatively out-of-date picture of distant parts of the network.

Routing protocols have been developed to ameliorate these problems, but like multicast protocols, they consume processing power and can only solve the problem to a limited degree. For example, if the network conditions change faster than the shortest time it takes a message to travel across the network, routers will always be out of date with respect to current network conditions, and thus make suboptimal routing decisions. Thus, existing QOS protocols need to deal with cases where not all of the desired resources are still available by the time the protocol requests reach the node(s) holding those resources. In a network with rapidly changing conditions, it is difficult for the protocol to successfully “seize the moment” to allocate a set of resources that are dispersed across the network. Existing QOS protocols must use various allocation and error recovery techniques that are complicated and suboptimal.

Thus it can be seen that there is a need for a method of communicating to a plurality of network nodes in parallel that can be applied to real-world problems such as network routing.

SUMMARY OF THE INVENTION

In accordance with this need, a method for communicating with multiple network nodes is provided in which each node of a network has a wireless link that allows data to travel to and from the nodes in parallel, thereby taking advantage of the inherent broadcast capabilities of wireless media. The method may be used for multicasting or broadcasting in general as well as for specialized functions such as maintaining a network cache and maintaining network routing information. Each node may be a router or similar device that uses its wireless link to transmit local routing data messages to a central server. The central server then processes the local routing data to update a routing database. Because all node transmission reach the central server essentially at the speed of light, the routing database will represent a nearly instantaneous and accurate picture of the network routing topology. The central server then broadcasts the routing database (or updates to the routing database) to all of the nodes in the network using the wireless medium. The nodes will use the routing database to efficiently route network data in order to ensure efficient routing and to maintain the appropriate Quality of Service (QOS).

Alternatively, each node may broadcast a local routing data message to the other nodes in the network via wireless medium. Each node then processes the local routing data messages received from the other nodes to maintain its own copy of the routing database. This eliminates the need for a central server, although a central server may be used concurrently.

Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying figures.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the drawings, wherein like reference numerals refer to like elements, the invention is illustrated as being implemented in a suitable computing environment. Although not required, the invention will be described in the general context of computer-executable instructions, such as programs, being executed by a computing device. Generally, programs include routines, other programs, objects, components, data structures, dynamic-linked libraries (DLLs), executable code, etc. that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multi-processor systems, microprocessor based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, parts of a program may be located in both local and remote memory storage devices.

With reference toFIG. 1, an exemplary system for implementing the invention is shown. The system includes a general purpose-computing device20, including a processing unit21, a system memory22, and a system bus23that couples various system components including the system memory to the processing unit21. The system bus23may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory includes read only memory (ROM)24and random access memory (RAM)25. A basic input/output system (BIOS)26, containing the basic routines that help to transfer information between elements within the computing device20, such as during start-up, is stored in the ROM24. The computing device20further includes a hard disk drive27for reading from and writing to a hard disk60, a magnetic disk drive28for reading from or writing to a removable magnetic disk29, and an optical disk drive30for reading from or writing to a removable optical disk31such as a CD ROM or other optical media.

The hard disk drive27, magnetic disk drive28, and optical disk drive30are connected to the system bus23by a hard disk drive interface32, a magnetic disk drive interface33, and an optical disk drive interface34, respectively. The drives and their associated computer-readable media provide nonvolatile storage of computer readable instructions, data structures, programs and other data for the computing device20. Although the exemplary environment described herein employs a hard disk60, a removable magnetic disk29, and a removable optical disk31, it will be appreciated by those skilled in the art that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, Bernoulli cartridges, random access memories, read only memories, and the like may also be used in the exemplary operating environment.

The computing device20may operate in a networked environment using logical connections to one or more devices within a network63, including another computing device, a server, a network PC, a peer device or other network node. These devices typically include many or all of the elements described above relative to the computing device20. The logical connections depicted inFIG. 1include a land-based network link51, for which there are many possible implementations, including a local area network (LAN) link and a wide area network (WAN) link. Land-based network links are commonplace in offices, enterprise-wide computer networks, intranets and the Internet and include such physical implementations as coaxial cable, twisted copper pairs, fiber optics, and the like. Data may transmitted over the network links51according to a variety of well-known transport standards, including Ethernet, SONET, DSL, T-1, and the like. When used in a LAN, the computing device20is connected to the network51through a network interface card or adapter53. When used in a WAN, the computing device20typically includes a modem54or other means for establishing communications over the network link51, as shown by the dashed line. The modem54, which may be internal or external, is connected to the system bus23via the serial port interface46. In a networked environment, programs depicted relative to the computing device20, or portions thereof, may be stored on other devices within the network63.

In the description that follows, the invention will be described with reference to acts and symbolic representations of operations that are performed by one or more computing devices, unless indicated otherwise. As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner well understood by those skilled in the art. The data structures where data is maintained are physical locations of the memory that have particular properties defined by the format of the data.

However, while the invention is being described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various of the acts and operation described hereinafter may also be implemented in hardware.

Referring toFIGS. 2 and 3, a preferred embodiment of the invention is shown as being implemented on an exemplary computer network63. As best shown inFIG. 2, the exemplary computer network63includes a plurality of nodes64and may be linked to one or more other networks90. Each of the nodes64is a personal computer, server, workstation, or other computing device, and includes many or all of the components shown inFIG. 1with respect to the computing device20. The nodes64are linked for network communication with one another through a series of conventional network links51. As best shown inFIG. 3, each node64has a processing unit21, a system memory22, a network interface card53linked to one another by a system bus23, and may also have several components in addition to those described inFIG. 1, including a network interface driver74, and a wireless interface79comprising a wireless interface driver78and a wireless interface card76. The node64is communicatively linked to at least one of the network links51. The wireless interface79is communicatively linked to an antenna80and a transceiver82over a network link51. A communications program84is executable by the processing unit21to cooperate with the wireless driver78in order to send and receive data over the wireless medium66via the wireless interface79. Specifically, the wireless interface driver78converts messages from the communication program84into a transmissible format required by the wireless interface card76. The wireless interface card76, in turn, converts the message into a physical transport format in order to transmit the messages through the wireless medium66. The transceiver82receives the physical message from the wireless interface card76, creates the actual signals required for transmission over the wireless medium66and sends those signals to the antenna80for transmission. The wireless interface driver78also converts signals received through the wireless medium into messages that the communication program84can relay to the appropriate part of the node64.

Referring again toFIG. 2, each node64is capable of communicating with a wireless medium66in order to send and receive messages in parallel to and from a plurality of other nodes. The wireless medium66may include one or more wireless networks, low-earth orbiting satellites, geosynchronous orbiting satellites, cellular transmission sites, microwave relays, and the like, which communicate over one or more portions of the light spectrum. It is contemplated that the network63may cover a geographic area of any size. For example, the network63may encompass an entire county and require only one transmission tower in the wireless medium66, or it may be worldwide, and require multiple satellites. It is also contemplated that the networks90may also implement the invention, thereby allowing them to achieve parallel communication internally, while communicating with the network63in a conventional manner.

To send a message from one of the nodes64to a group of other nodes, and to process the message once received, the communication program84(FIG. 3) may execute the procedure ofFIG. 4a. At step98, the communication program84remains in a wait state until a predetermined event, such as a multicast message becoming available to send, or until a predetermined interval of time passes. At step100, the communications program84attaches a multicast group identifier to the message. The multicast group identifier represents the group of nodes to which the message is intended, and may also represent the entire set of nodes on the network63. The communications program84then broadcasts the message to the nodes64of the network63via the wireless medium66at step102. It then returns to a wait state at step98.

To handle an incoming multicast message, the communication program84may execute the steps of the flowchart ofFIG. 4b. At step104, the communication program84remains in a wait state until it receives a multicast message. When the multicast message arrives, the communication program84proceeds to step106, during which the communication program84reads the group identifier of the message to determine whether the receiving node is a member of the multicast group. If the receiving node is not a member, the communication program84running on that node ignores the message at step108. If the receiving node is a member, then the communication program84processes the message at step110. Steps104-108may also be performed by the wireless card76using hardware or software logic on the card

The communication program84on the sending node may also send the broadcast or multicast message over a wireless channel that is dedicated to a particular multicast group of nodes. Similarly, the communication program84running on a receiving node in that group may monitor the dedicated multicast channel and treat any message received over that channel as a message that needs to be processed. If a dedicated channel is used in this manner, it would not be necessary for the communication program84of the sending node to add a multicast group identifier to the message. Having a dedicated multicast channel may be especially useful when the multicast group is relatively stable and well-defined, or when only a small number of multicast groups is required.

Referring toFIG. 5, an example of how the invention may be used to maintain a network cache is shown. The illustrated network63has a plurality of nodes, but only the nodes99, hereinafter referred to as “cache nodes,” are used to maintain copies92of the network cache. To maintain the coherency of the network cache, each of the cache nodes99sends conventional cache updates to the other nodes by multicasting the updates over the wireless medium66as described above and shown inFIG. 4a. Since this multicast group is well-defined, it may be preferable to have a dedicated wireless channel over which the updates can be sent and received. Each copy92of the network cache is typically maintained on a separate computer (not shown) coupled to, but not necessarily co-located with the node99. The network cache may contain web pages, audio and video files and other information to make it available when needed for speed and consistency. Although the logic for actually updating a network cache is well-known, the invention allows the copies92of the cache to be updated throughout the network in parallel using a single transmission This results in a very large savings of network bandwidth and processing overhead when, for example, updating large web sites and/or video sites that may consist of hundreds of megabytes of data. It is contemplated that the cache node99may be a router or similar device, and that the functions of sending and receiving routing updates as well as sending and receiving broadcast cache updates may be performed by the communication program84and wireless interface79on the cache node99. It is also contemplated that the cache updates may be performed by using the land-based links51in the event the wireless link fails.

Referring toFIGS. 6-8, an embodiment of the described method is used to maintain routing information and QOS in a network63. As best shown inFIGS. 6 and 7, each node64of the illustrated network is implemented as a router, gateway, or similar device and communicates via the wireless medium in the same manner as the exemplary node64ofFIG. 3. The node64also includes a local routing program71to conventionally collect local routing data and transmit the local routing data via the communication program84and over the wireless medium66to a central server68. The node64may also include a QOS program85for requesting resources, such as a network route having the needed performance characteristics for a communication session, from the central server68in order to maintain the appropriate QOS.

As shown inFIG. 6, the maintenance of the routing information is centralized at the central server68, and thus it is feasible to implement the central server68as a powerful computing device that is optimized to process large quantities of routing data and to make decisions regarding the assignment of network buffers, links, routes, and the like to specific communication sessions based on their QOS needs Also, each of the nodes64in this embodiment would not need to have the ability to make routing decisions although it may be desirable that they retain this ability in case they lose contact with the central server68.

As best shown inFIG. 8, the central server68includes many or all of the components of the computing device20shown inFIG. 1. Like the nodes64, the central server68includes a wireless interface79comprising a wireless interface driver78and wireless interface card76. The wireless interface79is communicatively linked to a wireless antenna80via a transceiver82. A global routing program96sends and receives routing data via the communication program84as previously described. While not shown inFIG. 6, the central server68may also be linked to the nodes64via land connection in case the wireless communication fails.

The central server68executes a global routing program94and a global QOS program95. The global routing program94uses the local routing data received from the nodes64to update a routing database70. The routing database70represents the current routing topology of the network, including the availability of the routes and the traffic along the routes. The global QOS program95receives requests for resources from the nodes64and, when the resources are available, allocates those resources by communicating with the appropriate nodes64in parallel via the wireless link. For example, a node64needing to transfer a large file may request that a high-bandwidth data path through the network63be reserved. The QOS program may then respond by choosing the best available route through the network for the transfer and attempting to allocate the CPU time and buffers needed in the various routers along the route using a standard QOS protocol.

In order to provide the local routing data to the central server68so that the routing database70can be maintained, the local routing program71(FIG. 7) executes on the node64according to the flowchart ofFIG. 9. At step150, the local routing program71waits for an interval of time to elapse before proceeding to the next step. This interval may correspond to predefined update interval. Alternatively, the local routing program71may wait for an event, such as a significant change in the data traffic at the node64, before proceeding. At step152, the local routing program71conventionally collects the local routing data, which may include the status of communication between that node and any adjacent nodes, the volume of the data traffic at the node and the latency and error rate being experienced on each link attached to the node. At step154, the local routing program71creates a message containing the local routing data, and attaches an origin identifier to identify the node from which the message is being sent. At step156, the local routing program71transmits the message to the central server68via the wireless medium66, using a broadcast or multicast.

To maintain the routing information in the network and to provide the latest version of the routing database70to the nodes64, the global routing program96executes on the central server68according to the flowchart ofFIG. 10. It is assumed that the central server68starts the procedure with an initial version of the routing database70. This initial version may be determined dynamically by the server and represent the current state of the network upon entry into the procedure ofFIG. 10or it may be one that is automatically loaded by the central server68at initialization.

At step160, the global routing program96waits for the receipt of local routing data from the nodes64. It is contemplated that the global routing program96may wait for a predetermined number of updates to be received before continuing to the next step. For example, the global routing program96may wait until at least 50% of the nodes have reported their local routing data. Alternatively, the global routing program96may wait for a predetermined interval and then proceed with the remaining steps, regardless of how many updates have been received from the nodes64. At step162, the global routing program96updates the routing database70with the local routing data received from the nodes64. At step164, the global routing program96creates a routing update message representing the update made to the routing database at step162. Alternatively, the routing update message may include the updated routing database itself. At step166, the global routing program broadcasts the routing update message to the nodes64. The program then returns to a wait state at step160.

To allocate network resources in order to maintain the proper QOS on the network63, the central server68and one or more of the nodes64can perform the procedure ofFIG. 11. At step200, the QOS program85on a node64forms a request for a resource based on a request received from a personal computer, server, or other client of the network. At step202, the QOS program85transmits the request for a network resource to the central server68via the communication program84and the wireless medium66using a standard QOS protocol. The central server68receives the request and executes the global QOS program95to process the request. The global QOS program95may then wait for a certain interval in order to give other nodes the opportunity to submit requests. At step206, the global QOS program95attempts to allocate the requested resources over the wireless medium66using a QOS protocol. Such an attempt may involve repeatedly contacting the various nodes from which the resources will be required, looking for alternative resources, waiting for acknowledgments from the nodes, and the like. If the attempt is successful, then the global QOS program95sends a message to the requesting node indicating that the request has been granted at step212. If the attempt is unsuccessful, then the global QOS program95transmits a denial to the requesting node at step210.

In another embodiment, the nodes64of the network depicted inFIG. 6may transmit and receive local routing data to and from one another without the use of the central reservation server68. To maintain the routing database70according to this embodiment, the local routing program71may execute event loops182and184asynchronously on a node64as shown inFIG. 12. At step170of event loop182, the local routing program71may be in a wait state until a predetermined event occurs, similar to the wait state described in step160ofFIG. 10. At step172, the local routing program71collects the local routing data in a well known manner. At step174, the local routing program71creates a local routing message containing the local routing data, and attaches an origin identifier representing the node from which the-message is being sent. If there are other, non-router nodes in the network, the local routing message may also have a multicast group identifier that corresponds to the group of router nodes. The receiving nodes may use the multicast group identifier to determine whether to process or ignore the local routing message. Alternatively, the local routing program71may select a channel that is dedicated to the router nodes. At step176, the local routing program71broadcasts the message to each of the other nodes64of the network via the wireless medium66. The process then returns to step170.

In event loop184, the local routing program waits until it receives local routing messages containing local routing data and having origin identifiers from the other nodes64via the wireless medium66at step178. The local routing program71then updates the routing database70using the local routing data received from the other nodes64at step180. The process then returns to step178.

To maintain the proper QOS on the network63, the nodes64ofFIG. 6may perform the procedure of the flowchart ofFIG. 13. At step250, the QOS program85of a node forms a message that includes a request for a network resource based on the QOS needs for the data traffic it is currently handling. The request identifies the nodes from whom the resource is being requested as well as the nature of the resource being requested. At step252, the QOS program85broadcasts the request via the communication program84and the wireless medium66to the other nodes64using a QOS protocol. At Step254, the QOS program85on each node receiving the request processes the request by referring to the routing database70and determining whether the resource is available. At step256, each receiving node allocates the requested resource using a standard protocol, such as a two-phase commit protocol. The process then returns to step250.

In view of the many possible embodiments to which the principals of this invention may be applied, it should be recognized that the embodiment described herein with respect to the drawing figures is meant to be illustrative only and should not be taken as limiting the scope of the invention. For example, a QOS resource request and new routing data as described above may be sent in a single message or as separate messages. Also, the invention may be used for other broadcasting or multicasting data other than the types of data described herein.

It should also be recognized that the ordering and the specific implementation of the program steps described above and depicted in the flowcharts ofFIGS. 4,10-13is may be altered in obvious ways.

Those of skill in the art will recognize that the elements of the illustrated embodiment shown in software may be implemented in hardware and vice versa or that the illustrated embodiment can be modified in arrangement and detail without departing from the spirit of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.