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From: ron@topaz.rutgers.edu (Ron Natalie)
Newsgroups: comp.dcom.lans
Subject: Re: Bridge Questions
Message-ID: <13673@topaz.rutgers.edu>
Date: Mon, 3-Aug-87 16:47:09 EDT
Article-I.D.: topaz.13673
Posted: Mon Aug  3 16:47:09 1987
Date-Received: Tue, 4-Aug-87 04:51:17 EDT
References: <323@pollux.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 35

There are several ways to interconnect two ETHERNET cable segments.

REPEATER:
    The first is via a repeater.  A repeater is theoretically the fastest
    and easiest.  In essentially transfers all the bits in real time from
    one cable to the other.  The distance requirements remain and no packet
    filtering occurs.  The ETHERNET specification permits only two repeaters
    in the path between any two stations.  No cycles are permitted in the
    topology.  An example is the DEC DEREP.


DATA LINK BRIDGE:
    A data link bridge copies an entire packet into it's memory and then
    repeats it on the other segment.  The bridge may learn from examining
    traffic which stations are on which segment and avoid passing datagrams
    for local traffic to the other segment.  However, broadcast and multicast
    datagrams must be sent accross all segments.  Since the bridge acts as
    a station rather than a repeater the cable length and maximum number
    requirements are removed, however, no cycles may be present in the
    topology.  Examples of data link bridges are the DEC LANBridge 100,
    the Bridge Communications IB/2, and the Ungermann/Bass DL1.

PROTOCOL ROUTERS:
    Routers or gateways are similar to the data link bridges in that they
    read in the entire packet and resend it on the other segment but they
    actually examine the protocol dependent data in the packet to decide
    where and when to forward the packets.  These routers can function to
    the limit of the protocol and the topology can get quite complex with
    cycles and redundant paths.  The disadvantage is that the router must
    know about every protocol it intends to route.  Some routers can deal
    with more than one protocol, many only one.  Each segment must be
    interconnected with routers for each protocol in use.  IP routers
    include CISCO and Proteon, DEC also sells DECNET routers.

-Ron