Method for interconnecting local area networks or network segmen

Details Method for interconnecting local area networks or network segmen Method for interconnecting local area networks or network segmen

1995-05-15

1997-09-23

Kizou, Hassan

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

370470, 370444, H04L 1228, H04B 7212, H04J 316

Patent

active

056712243

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a method for interconnecting local area networks or network segments, and to a local area network bridge
A local area network (LAN) is a local data network taking care of traffic between workstations connected to it, such as PCs, and various devices providing services to the workstations. A basic LAN configuration comprises a physical transmission path, i.e. cabling, a network server, workstations connected to the cabling by means of adapter cards, and a network software. ALAN is typically located in a single building or in several buildings located close to each other, e.g. at one office of a specific organization or company. Recently, however, there has been an increased demand to interconnect individual LANs into larger networks. For such purposes, the above-described basic components will not suffice.
Equipments required to interconnect LANs are typically classified in accordance with the OSI (Open Systems Interconnection) model of the ISO (International Standards Organization). The OSI model aims at creating a framework for standards applied in data transmission between open systems. The model comprises seven superimposed layers the tasks of which have been specified whereas their implementation has been left open. The OSI model listed at the end of the specification).
The devices used in the interconnection of LANs, i.e. the repeater, the bridge, and the router, will be described in short below.
The repeater is the simplest means used in the interconnection of LANs or LAN segments. The repeater operates on the lowest OSI layer (layer 1), i.e. on the physical layer. The repeater amplifies the bit stream and forwards all traffic over it from one network segment to another. The repeater is thus used to increase the physical length of the network, and it can be used only when the networks to be interconnected are fully identical (or differ only in the transmission medium). Segments interconnected by the repeater form a single logical network.
The bridge operates on the next OSI layer (layer 2), i.e. on the data link layer. Even though the data link layer is mainly independent of the physical transmission medium used, some of its functions, however, are dependent on the physical transmission medium. For this reason, the data link layer includes a so-called MAC (Media Access Control) sublayer in some network architectures. The MAC sublayer provides access to the transmission path, i.e. it takes care of functions most probably associated with the characteristics of the physical transmission path. Bridges typically operate on the MAC sublayer. The function of the bridge is to monitor frames transferred over the LAN and to transfer them from one network to another on the basis of the physical address of the data packets. Only frames having a destination address indicating transmission to the side of the other network are able to cross the bridge. The bridge thus acts as an insulator which reduces the load in other network portions. The bridge does not analyze more closely what the frames transport and it ignores the higher-level protocol transferred in the frames. In other words, the bridge is protocol-independent, and so it can be used to interconnect networks utilizing protocols of different types (TCP/IP, XNS, OSI, NetBios, etc.).
The bridge contains a so-called routing table, which is updated by the bridge on the basis of the addresses of the transmitting parties of frames received by the bridge. The routing table indicates to the bridge behind which interface a specific station is currently located. In other words, the bridge is able to "learn" station locations so that new stations can be added to the network without having to reconfigure the bridge.
The router operates on the third OSI layer, i.e. on the network layer. Routers know the higher protocols used in the LAN traffic and route messages by means of the addressing mechanisms of these protocols. The router forwards the frame (to another router or to a destination station) on the basis of the d

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Grimshaw, "LAN Interconnections Technology", LAN TECHNOLOGY TELECOMMUNICATIONS, Feb. 1991, pp. 25-32.

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