Path: utzoo!mnetor!uunet!wyse!weitek!pyramid!prls!philabs!aecom!glen
From: glen@aecom.YU.EDU (Glen M. Marianko)
Newsgroups: comp.dcom.lans
Subject: Ethernet-Ethernet Bridges
Message-ID: <1716@aecom.YU.EDU>
Date: 6 Apr 88 00:39:30 GMT
Organization: Albert Einstein College of Medicine, NY
Lines: 41
Keywords: Ethernet Mac Layer Bridge


We are planning a campus-wide ethernet here and are running into some
hair-pulling questions, specifically about mac-layer bridges.

We have about 6 buildings that will be wired with either a thick
or thin riser cable (any arguments about preference for one or
the other are welcome).  One building will be the "center" or hub
of the network with the other buildings connecting to the hub
in a star fashion using ethernet fiber optic repeaters (multiport
at the hub).

We thought it would be a good idea to incorporate mac-layer bridges
in the design with, at bare minimun, a learning ethernet-ethernet bridge
at every building (between the riser and fiber repeater to the hub).
We came to this conclusion for two reasons: first, maximizing
throuput by deleting packets that would propagate where they are
not needed; second, so that we won't exceed the number of repeaters
in the network.

In reading a recent issue of LAN Magazine, it became apparrent that
different bridges have different filtering/passalong speeds.
DEC's was rated the fastest, but it uses a VAX for network management;
Retix was the cheapest but no management I could find; Bridge IB/3
seems like a nice compromise using a standalone manegement station
with backup links, and so on.

Big question is, are we shooting our network in the foot by putting
in bridges - in other words will the bridge become the bottleneck
before the ethernet does?  I've heard all the comments about
typical ethernet usage being about T-1 speed, but what about the
times it bursts - the network could still theoreticaly service more when
that happens?  What would be the sense of having fiber between
bridges if the bridge would reduce us to 1-2 megabits/sec.?

Anyone have any bridge preferences?  IB/3 seems like the best, but
doesn't come cheap.  It also seems like it could support 2 fiber
links between other IB/3s in a ring fashion providing better
network reliability at the hub (now just a fiber patch panel).

-- Glen Marianko
   glen@aecom.yu.edu