Multiplex communications – Pathfinding or routing
Reexamination Certificate
1998-11-24
2002-09-17
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
C370S395520, C370S395530, C370S395540, C370S401000
Reexamination Certificate
active
06452921
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to data communication and in particular to data communication in a computer network. Still more particularly, the present invention relates to method and system in a computer network for maintaining source-route information at a router located within a default communication path between two devices when the router is bypassed by shortcut communication between the two devices.
2. Description of the Related Art
Generally speaking, two broad categories of communication protocols are utilized in data communication networks: broadcast protocols and unicast (point-to-point) protocols. In data communication networks that implement a conventional broadcast protocol, a source station transfers data to a destination station by broadcasting a data packet containing the destination station's address to all stations attached to the network. In response to sensing a data packet containing its address, the destination station receives the data packet from the network; all other stations ignore the data packet. Because every data transfer between a source station and a destination station in a broadcast network requires broadcasting data packets in this manner, broadcast networks are designed to support only a relatively small numbers of stations. A conventional broadcast network's limited bandwidth would be overwhelmed by the number of broadcast packets if a large number of stations were attached.
Because of the bandwidth limitations of individual broadcast networks, broadcast networks are often implemented as a series of interconnected subnetworks (or subnets). Such a network architecture is also a natural outgrowth of the desirability of interconnecting each new local area network (LAN) with preexisting LANs. Communication between subnetworks that each form a portion of a larger internetwork is accomplished by devices called routers, which provide layer-
3
(i.e., network) connectivity between subnetworks according to the International Organization for Standardization Open Systems Interconnection (ISO/OSI) model. Thus, when a source station desires to transfer data to a destination station in a different subnetwork of a broadcast internetwork, the source station broadcasts, on its subnetwork, a data packet containing the address of a destination station. The broadcast data packet is received by each station in the source station's subnetwork, including a router. In response to sensing the destination station's address, the router receives the data packet from the source station's network and broadcasts the data packet on the destination station's subnetwork, to which the router is also attached. As described above, in response to sensing a data packet specifying its address, the destination station receives the data packet from its network, while all other stations on the destination station's subnetwork ignore the data packet.
Because of the size limitation and inherent inefficiency of networks that implement broadcast protocols, there has been increased interest in unicast protocols that permit point-to-point data communication. One emerging network technology that permits such connection-oriented communication is asynchronous transfer mode (ATM). An ATM protocol is defined in “ATM User-Network Interface (UNI) Signaling Specification, Version 4.0,” which is promulgated by the ATM Forum Technical Committee and incorporated herein by reference. In an ATM network, a source station negotiates a connected path to a desired destination station before the source station proceeds to transmit its data to the destination station. The ATM protocol defines the communication required to establish such a point-to-point connection. Once a point-to-point connection has been established, the source station transmits its data only to the destination station using unicast frames. Thus, unicast protocols, such as ATM, address the shortcomings of conventional broadcast protocols by providing high speed, low bandwidth communication.
When only communication speed and data throughput are considered, it would be desirable to replace the installed base of non-ATM protocol networks (e.g., Wide Area Networks (WANs), Local Area Networks (LANs), Internet Protocol Networks) with high speed connection-oriented network technologies such as ATM. However, because the expense of replacing the enormous number of installed broadcast networks is prohibitive and because some of the non-ATM protocol networks have features that are not directly supported by ATM protocol networks, industry has taken a gradual approach to upgrading network technologies. Under this approach, the communication industry has opted to move toward ATM protocol networks while simultaneously continuing to support the vast installed base of non-ATM protocol networks and the network and link layer protocols operating on the non-ATM networks until the non-ATM networks are phased out. The key to this strategy is empowering the ATM protocol networks to be able to support non-ATM protocols, and to be able to support non-ATM features that users (and user's systems) have come to expect and rely upon.
The telecommunications industry has opted to provide such support and supply such features via various overlay schemes. These overlay schemes, while representing a number of different implementations, all support any non-ATM capability with a logically separate protocol that is logically overlaid onto a base ATM protocol network. The logically overlaid protocol is then utilized to allow non-ATM protocol networks to interact with ATM protocol networks as if the ATM protocol networks were a part of, and hence recognize the protocols and support the features of, non-ATM protocol networks.
One scheme for supporting conventional LAN technology in the context of ATM includes the implementation of a Logical IP Subnetwork (LIS), which is a ISO/OSI layer-
3
subnetwork within an ATM network. The ATM network serves as a direct replacement for the physical LAN segments connecting traditional layer-
3
source and destination stations (collectively, end stations) and routers. Communication between end stations within the same LIS is accomplished utilizing the ATM protocol. In order for a source station to establish a connection with a destination station within the LIS, the source station must learn the ATM address of the destination station. Accordingly, the source station sends an ATM Address Resolution Protocol request (ATMARP —Request) to an ATM Address Resolution Protocol (ARP) Server, which resolves the destination station's layer-
3
address (i.e., the address by which the destination station is identified with respect to its subnet) into an ATM address that the source station can utilize to obtain a point-to-point connection. By contrast, communication between end stations in different LISs is performed as if the end stations resided in different traditional LANs. The source station transmits the data traffic to a router based on the layer-
3
address of the destination station. After determining the appropriate destination address (and protocol) by reference to a table, the router then forwards the data to the appropriate destination LIS or to a second router, if the router on the source LIS is not a member of the destination LIS.
Another mechanism for supporting conventional broadcast technology in an ATM environment is an emulated LAN (ELAN), which supports the use of IEEE 802 LAN protocols, such as Ethernet and Token Ring protocols, within an ATM protocol network. Communication within an ELAN is governed by a LAN emulation (LANE) protocol, such as “LAN Emulation Over ATM Version 2—LUNI Specification” (AF-LANE-0084.000), which is promulgated by the ATM Forum and incorporated herein by reference. The LANE protocol defines a service interface for higher layer (that is, network layer) protocols, which is identical to that of legacy LANs, and requires that data sent across the ATM network are encapsulated in the appropriate LAN MAC (medium a
Alexander, Jr. Cedell Adam
Gardo Russell Eugene
Gorti Brahmanand Kumar
Stokes, Jr. Olen Lee
Bracewell & Patterson LLP
Chin Wellington
Duong Frank
International Business Machines - Corporation
Woods Gerald R.
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