Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-07-02
2004-01-20
Pham, Chi (Department: 2667)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06680942
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to peer to peer transport services provided by routers or switches, etc. in a computer network, and more particularly to directory services provided for peer entities.
BACKGROUND OF THE INVENTION
A router can provide peer to peer services for routing packets on a computer network. For example, a router, which is generally a layer 3 switching device since it depends upon the IP destination address for routing decisions, may provide layer 2 switching service such as DLSw switching. DLSw switching is an example of peer to peer services provided by a router.
An example of peer-to-peer routing is the Advanced Peer to Peer Network (APPN) method developed by IBM Corporation. The APPN system developed from an earlier system having a mainframe computer controlling all networking functions, including route computations. The mainframe connects to “nodes,” and the nodes connect to terminals, either directly or indirectly through terminal controllers. Packets were routed through the network of nodes by source routing, where the mainframe computer computed the path for source routing. In APPN, a group of nodes are defined as “peer” nodes. Links are established between the peer nodes, for example by leased telephone lines, etc. End stations are attached to peer nodes, either directly or indirectly through “terminal controllers”. Those end stations attached to a peer node are said to be in the “domain” of the peer node. The SNA architecture is described by Andrew Tanenbaum in his book
Computer Networks Second Edition,
published by Prentice Hall Publishing Co., Copyright 1988, all disclosures of which are incorporated herein by reference, especially pages 46-47. When a source logical unit in a source station decides to set up a “conversation” with a “destination logical unit” in another station, the peer node whose domain the source end station is in computes a route through other peer nodes and links of the APPN system. The first end station then addresses its packets for the conversation by means of the route computed by the peer node. The packet travels through the APPN network as a source routed packet as it travels along the computed route. In computing the route, the peer node makes use of a database of peer nodes, links, characteristics of links, and available logical units. The peer node then computes an optimum route, with the optimum being dependent upon route characteristics requested by the source end station. When a packet arrives at a peer node for routing to a destination station, no decision about identifying the protocol of the packet need be made, as all packets are under the same protocol, the APPN protocol. Each node in the APPN network may keep a cache of a Directory Database for locating peer nodes, as explained by Jesper Nilausen in his book
APPN Networks,
published by John Wiley & Sons, Copyright 1994, all disclosures of which are incorporated herein by reference, especially pages 43-50. Problems with directory databases cached in each node arise when many nodes broadcast to find the same end station, and the consequent use of considerable network bandwidth for redundant searches.
A further example of peer to peer routing services comprises DLSw, or Data Link Switching, as defined in RFC 1795 published by the Internet Engineering Task Force in April 1995, and available from the Web Site at URL www.ietf.org. All disclosures of RFC 1795 are incorporated herein by reference.
In the DLSw peer to peer example, when a router receives a packet, the router determines whether the packet is to be forwarded by DLSw protocol. For example, the router may have local area networks (LANs) using a variety of protocols connected thereto, and the router must determine the protocol of the packet. The router determines the protocol of the packet by identifying the port on which the packet arrived at the router, by reading fields of the packet at various offsets from the beginning of the packet, etc. In the event that the router determines that the packet is to be forwarded by DLSw protocol, the packet is encapsulated with a SSP header (as defined in RFC 1795), a cyclic redundancy check (CRC) trailer field, and some other fields. The encapsulated packet is then transmitted over a TCP/IP connection to a peer router, which also provides DLSw service. The TCP/IP connection is established through a network “cloud” potentially having many routers providing DLSw service connected thereto.
A router providing DLSw service is referred to herein as a “DLSw router”. The DLSw service is referred to as “DLSw switching”, as the service occurs in layer 2 of the Internet Protocol.
In some networks, a DLSw router may be connected to only one LAN, for example a source routing bridged (SRB) network based on IEEE 802.5 token rings and bridges. Packets received by the DLSw router from the SRB network may all be routed using the DLSw protocol. In other networks, a router may have a port connected to an IEEE 802.5 token ring, may have another port connected to an IEEE 802.3 Ethernet LAN, an FDDI token ring LAN, etc. An IEEE 802.5 token ring may have packets transmitted thereon under SNA protocol, and addressing of SNA packets to the destination station is in layer 2 fields. An IEEE 802.3 Ethernet packet has addressing to the destination station in layer 2 and in layer 3 fields. Also, packets transmitted under TCP/IP protocol have addressing to the next hop router in layer 2, and to the destination station in the layer 3 IP destination address field, etc. The router receiving packets from a variety of LAN technologies and LAN protocols reads the address fields and makes routing decisions. In the event that a packet is routed from a first LAN using a protocol which is incompatible with the protocol of the next LAN, then the router must re-build the packet before transmitting the packet onto the next LAN. For some packets, the decision is to route the packets by DLSw switching.
In the event that the routing decision is to route a packet by DLSw switching, then a router on the same LAN as the source end station, hereinafter the “source LAN” and the “source router”, finds a peer router (hereinafter the “destination router”) offering DLSw service, where the destination router can reach the destination end station. The destination router is ordinarily connected to the same LAN as is the destination end station, hereinafter the destination LAN. The source router must identify the proper peer router to serve as the destination router.
Routers offering DLSw service transfer encapsulated packets between themselves using TCP/IP protocol through a network cloud, and they are referred to as “peer DLSw routers”. There may be many, for example, a few hundred peer DLSw routers communicating through a TCP/IP network cloud, and for a further example, there may be several thousand. A source DLSw router that receives a packet from an end station and makes a routing decision that this packet is to be encapsulated and routed under DLSw protocol must select the proper destination DLSw router. The source router then places the destination router address in the proper fields of a TCP/IP packet so that the selected destination DLSw router receives the encapsulated packet through the TCP/IP network cloud. Upon receipt of the encapsulated packet by the destination DLSw router, the destination DLSw router removes the encapsulation and transmits the packet onto the proper LAN so that the destination end station can receive the packet.
Selection of the destination router by the source router is ordinarily accomplished by the source router first checking an internal cache (hereinafter the DLSw cache) in order to learn if it already knows the proper destination router for the destination end station specified by the destination address of the packet. In the event that the DLSw cache in the source router does not have the necessary information, the source router then transmits a “CANUREACH” message to each of its DLSw router peers, as defined in RFC 1795. The CANUREACH message includes the address
Bales Scott
Denny Mark
Lautmann John
Mead Andrew
Thippeswamy Arunkumar
Cesari and McKenna LLP
Cisco Technology Inc.
Ly Anh-Vu H
Pham Chi
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