WO2003094010A1

WO2003094010A1 - Method and system to implement a simplified shortest path routing scheme in a shared access ring topology

Info

Publication number: WO2003094010A1
Application number: PCT/US2003/011435
Authority: WO
Inventors: William Anderson
Original assignee: Manticom Network, Inc.
Priority date: 2002-05-01
Filing date: 2003-04-15
Publication date: 2003-11-13
Also published as: AU2003230913A1

Abstract

A device, method, system and computer program product for implementing a simplified shortest path routing schema in a shared access ring topology (100) is provided. The present invention allows the routing of data packets on a bi-directional ring (100) by monitoring data from only a single direction of the ring (100). Yet, by implementing a two-phase approach and utilizing the TTL field (TTL) within packet headers, in an embodiment, a decision on which of two paths should be chosen as the shortest path in the ring topology can still be made.

Description

TITLE OF THE INVENTION

METHOD AND SYSTEM TO IMPLEMENT A SIMPLIFIED SHORTEST PATH ROUTING SCHEME IN A SHARED ACCESS RING TOPOLOGY

This application claims priority from U.S. Provisional Application Serial No. 60/376,564, filed May 1, 2002. The entirety of that provisional application is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to data networks and more particularly to devices and methods for ensuring maximum bandwidth utilization when data networking devices are connected in a ring topology.

Related Art

In a typical Internet Protocol (IP) network with multiple data paths to a destination, routing software may use the number of router/switch nodes traversed by the data path to determine the best path to route any given data. Typically, the path with the fewest routers/switches (i.e., intermediate nodes) is determined to be the chosen (shortest) path.

Today, such routing software monitors all data paths in an attempt to ascertain the shortest overall path. This requires that the router store characteristics of multiple paths and use such stored information during its determination of the shortest path.

An improvement on this routing technology can be implemented in a shared media ring topology. In a ring topology, all data traffic shares the same media, but each node on the ring is responsible for receiving data from one neighbor, via a ring interface and transmitting to the other neighbor, via the second ring interface. (In a ring, each node only has two neighbors.) Therefore, given the above, what is needed is a device, method, system and computer program product for implementing a simplified shortest path routing schema in a shared access ring topology. Such a device, method, system and computer program product would require only one path to be monitored to make a decision on which of two paths should be chosen as the shortest path in the ring topology.

SUMMARY OF THE INVENTION

The present invention meets the above-identified needs by providing a device, method, system and computer program product for implementing a simplified shortest path routing schema in a shared access ring topology. More specifically, the present invention consists of a device, method, system and computer program product for routing data packets on a bidirectional ring by monitoring data from only a single direction of the ring.

For example, in an embodiment, the method and computer program product of the present invention includes the steps of transmitting a first packet onto the network by a first node wherein the TTL field of the first packet is set to a first value, the first value is greater than the number of nodes in the network and each node decrements the TTL field by one as the first packet is passed through each node in the network. When the first packet is received by the first node, the number of nodes in the network is then determined by subtracting the value of the TTL field from the first value. A second packet transmitted by a second node is then received at the first node.

A shortest path to the second node can then be determined by examining the TTL field of the second packet.

An advantage of the present invention is that it eliminates the complexity of monitoring data from both directions of a ring to make routing decisions. An advantage of the present invention is that it may be implemented in packet ring networks, Optical Ethernet rings, Fiber Channel Rings, and the like.

Another advantage of the present invention is that it may be implemented in dedicated hardware or as part of a network processor. Further features and advantages of the invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears. Figure 1 is a block diagram illustrating a bidirectional ring communications system in which the present invention may be implemented according to one embodiment;

Figure 2 is a block diagram illustrating a packet header, according to an embodiment of the present invention, that is attached to each packet inserted on the ring communications system;

Figure 3 and Figure 4 are block diagrams illustrating the bidirectional ring communications system of Figure 1 and highlighting the operation of the present invention in an embodiment; and

Figure 5 is a block diagram of an exemplary computer system useful for implementing the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to an implementation of the present invention as illustrated in the accompanying drawings.

The present invention relates to a device, method, system and computer program product for implementing a simplified shortest path routing schema in a shared access ring topology.

Referring to Figure 1, a block diagram illustrating a bidirectional ring communications system 100 in which the present invention may operate is shown. As shown in Figure 1, bidirectional ring communications system 100 contains six add/drop nodes (i.e., nodes 1-6). In Figure 1, packets are shown as emanating from node 1 on both a counter-clockwise direction 102 and a clockwise direction 104 of ring communications system 100. The purpose of this is to convey routing information to the destination node (e.g., node 3).

Node 3 will see a packet on the counter-clockwise direction 102 of ring 100 with its "Time to Live" (TTL) field in the IP packet header set to "4" and a packet on the clockwise direction 104 ring with its TTL field set to "2." Node 3 will then be able to determine that the clockwise direction 104 of ring 100 is the shortest path to node 1.

The downside to the above-described approach is that bandwidth is utilized on both counter-clockwise direction 102 and clockwise direction 104 of ring communications system 100. Also, node 3 is required to examine packets on both directions 102 and 104 of ring 100. Figure 1 represents a conventional method for making shortest-path routing decisions.

The present invention is now described in terms of the above example. This is for convenience only and is not intended to limit the application of the present invention. In fact, after reading the following description, it will be apparent to one skilled in the relevant art(s) how to implement the following invention in alternative embodiments (e.g., networks having different number of add/drop nodes, etc.).

Referring to Figure 2, a header 200 which in an embodiment is attached to each packet that is inserted on ring 100 is shown. In such an embodiment, one field is defined and specially used — the TTL field 202.

As will be appreciated by those skilled in the relevant art(s), the remaining portion 204 of packet header 200 may contain any other defined fields or any other

(e.g., Ethernet, IP, etc.) packet header information normally included in the type of packets that flow through ring 100.

Generally, the node which originates the packet on ring 100 will set the TTL field equal to the number of nodes on ring 100 minus one (e.g., the value "5" as there are six nodes shown in Figure 1, and: 5 = 6 - 1). However, the actual setting of the TTL field is implementation specific (i.e., dependent on the implementation of ring 100). Normally, one node on the ring (e.g., the destination node) will remove the packet from the ring. In the unlikely case that there is no destination node, the packet will propagate around ring 100. Each node will decrement the value of TTL field 202 by one. When the packet returns to the originating node, the value of TTL field 202 will be reduced to zero and will then be removed from ring 100.

Referring now to Figure 3, a block diagram illustrating bidirectional ring communications system 100 and highlighting the first phase of operation of the present invention in an embodiment is shown. In this example case, node 3 sends a packet onto ring 100 with the destination of the packet equal to node 3. In this way, node 3 injects a packet, with TTL set to the "maximum" value onto ring 100 and is also responsible for removing it from ring 100. The "maximum" setting is implementation specific, and in an embodiment, may be set to a value greater than the expected number of nodes in ring 100 (e.g., in the example case of system 100 shown in Figures 1 and 3, any value greater than six).

Each node will decrement the value of TTL field 202 each time the packet passes through a node. When node 3 receives the packet, it will be able to determine the number of nodes on the ring by subtracting the value of TTL field 202 in the received packet from the "maximum" value it initially set. Referring now to Figure 4, a block diagram illustrating bidirectional ring communications system 100 and highlighting the second phase of operation of the present invention in an embodiment is shown.

Once the number of nodes on ring 100 is known, only the monitoring of packets in one direction of the ring will be required to decide which path needs to be selected as the shortest path. For example, in Figure 4, node 3 receives a single packet, originating from node 1, firom the clockwise direction 104 of ring 100. Since the received value of TTL field 202 (value = 2) is less than one-half of the total number of nodes on the ring (total number of nodes = 6), the shortest path to node 1 is clockwise direction 104. Similarly, if the received value of TTL field 202 of the packet was greater than one-half of the maximum number of nodes, the shortes direction would be counter-clockwise direction 102.

Thus, in an embodiment of the present invention, each node maintains a table that includes a record for each node in ring communications system 100. This table provides routing information for each of the nodes in ring 100 based on the two-phase procedure described above with reference to Figure 3 and Figure 4.

Example Implementations

The present invention (or any part(s) or function(s) thereof) may be implemented using (dedicated) hardware, software or a combination thereof and ma} be implemented in one or more computer systems or other processing systems. Ir fact, in one embodiment, the invention is directed toward one or more compute] systems capable of carrying out the functionality described herein. An example of ∑ computer system 500 is shown in Figure 5. The computer system 500 includes one or more processors, such as processor 504. The processor 504 is connected to ∑ communication infrastructure 506 (e.g., a communications bus, cross-over bar, oi network). Various software embodiments are described in terms of this exemplar) computer system. After reading this description, it will become apparent to a persor skilled in the relevant art(s) how to implement the invention using other compute] systems and/or architectures. Computer system 500 can include a display interface 502 that forwards graphics, text, and other data from the communication infrastructure 506 (or from i frame buffer not shown) for display on the display unit 530.

Computer system 500 also includes a main memory 508, preferably randorr access memory (RAM), and may also include a secondary memory 510. The secondary memory 510 may include, for example, a hard disk drive 512 and/or i removable storage drive 514, representing a floppy disk drive, a magnetic tape drive an optical disk drive, etc. The removable storage drive 514 reads firom and/or write; to a removable storage unit 518 in a well known manner. Removable storage uni 518, represents a floppy disk, magnetic tape, optical disk, etc. which is read by anc written to by removable storage drive 514. As will be appreciated, the removabh storage unit 518 includes a computer usable storage medium having stored thereii computer software and/or data.

In alternative embodiments, secondary memory 510 may include other simila devices for allowing computer programs or other instructions to be loaded intc computer system 500. Such devices may include, for example, a removable storagt unit 522 and an interface 520. Examples of such may include aprogram cartridge anc cartridge interface (such as that found in video game devices), a removable memor) chip (such as an erasable programmable read only memory (EPROM), o programmable read only memory (PROM)) and associated socket, and othe removable storage units 522 and interfaces 520, which allow software and data to be transferred from the removable storage unit 522 to computer system 500.

Computer system 500 may also include a communications interface 524 Communications interface 524 allows software and data to be transferred betweei computer system 500 and external devices. Examples of communications interface

524 may include a modem, a network interface (such as an Ethernet card), i communications port, a Personal Computer Memory Card International Associatior (PCMCIA) slot and card, etc. Software and data transferred via communication! interface 524 are in the form of signals 528 which may be electronic, electromagnetic optical or other signals capable of being received by communications interface 524

These signals 528 are provided to communications interface 524 via i communications path (e.g., channel) 526. This channel 526 carries signals 528 anc may be implemented using wire or cable, fiber optics, a telephone line, a cellular link an radio frequency (RF) link and other communications channels. In this document, the terms "computer program medium" and "compute] usable medium" are used to generally refer to media such as removable storage drive 514, a hard disk installed in hard disk drive 512, and signals 528. These compute] program products provide software to computer system 500. The invention is directec to such computer program products. Computer programs (also referred to as computer control logic) are stored in main memory 508 and/or secondary memory 510. Computer programs may also be received via communications interface 524. Such computer programs, when executed, enable the computer system 500 to perform the features of the present invention, as discussed herein. In particular, the computer programs, when executed, enable the processor 504 to perform the features of the present invention. Accordingly, such computer programs represent controllers of the computer system 500.

In an embodiment where the invention is implemented using software, the software may be stored in a computer program product and loaded into computer system 500 using removable storage drive 514, hard drive 512 or communications interface 524. The control logic (software), when executed by the processor 504, causes the processor 504 to perform the functions of the invention as described herein.

In another embodiment, the invention is implemented primarily in hardware using, for example, hardware components such as application specific integrated circuits (ASICs). Implementation of the hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s).

In yet another embodiment, the invention is implemented using a combination of both hardware and software.

Conclusion While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. For example, it should be noted that the present invention is not limited to ring topologies, but can be applied to other network topologies as would be apparent to those skilled in the relevant art(s). Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A method for making routing decisions for packets in a network, wherein each packet has a TTL field, comprising: transmitting a first packet onto the network by a first node in the network, wherein: the TTL field of said first packet is set to a first value; said first value is greater than the number of nodes in the network; and each node in the network decrements said TTL field by one as said first packet is passed through said each node; receiving said first packet by said first node, determining the number of nodes in said network by subtracting the value of said TTL field from said first value; receiving at said first node a second packet transmitted by a second node onto the network; and determining a shortest path to said second node by examining said TTL field of said second packet.

2. The method of Claim 1, wherein the network is a bidirectional ring communications system.

3. A computer program product comprising a computer usable medium having control logic stored therein for causing a computer to make routing decisions for packets in a network, said control logic comprising: first computer readable program code means for causing the computer to transmit a first packet onto the network by a first node in the network, wherein the

TTL field of said first packet is set to a first value, said first value is greater than the number of nodes in the network and each node in the network decrements said TTL field by one as said first packet is passed through said each node; second computer readable program code means for causing the computer to receive said first packet by said first node, third computer readable program code means for causing the computer to determine the number of nodes in said network by subtracting the value of said TTL field from said first value; fourth computer readable program code means for causing the computer to receive at said first node a second packet transmitted by a second node onto the network; and fifth computer readable program code means for causing the computer to determine a shortest path to said second node by examining said TTL field of said second packet.

4. The computer program product of Claim 3, wherein the network is a bidirectional ring communications system.