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From: koning@koning.enet.dec.com (Paul Koning)
Newsgroups: comp.dcom.lans
Subject: Re: FDDI question: bridges, routers, interoperability ...
Keywords: FDDI, bridges, routers
Message-ID: <22755@shlump.lkg.dec.com>
Date: 17 May 91 20:57:37 GMT
References: <1779@ariadne.csi.forth.GR>
Sender: newsdaemon@shlump.lkg.dec.com
Reply-To: koning@koning.enet.dec.com
Distribution: comp
Organization: Digital Equipment Co., distributed systems architecture
Lines: 57


|>Dear FDDI experts,
|>
|>We are planning to install 2 FDDI rings  and we are looking for comments
|>or experiences from users.
|>
|>Here are some questions:
|>
|>I have a host A connected to an ethernet segment. The ethernet segment is
|>connected on an FDDI bridge and the bridge on an FDDI ring. I have a
|>host B connected to an ethernet segment. The ethernet segment is connected
|>on a FDDI ethernet router and the router on the ring.
|>
|>My question is: Will A talk to B?
|>
|>The bridge will be Dec compatible translation bridge.

Yes.  At the datalink level, A talks to the router's FDDI port; the
router in turn forwards over its Ethernet port to B.  Since you said
that the bridge is a translating bridge, it will turn A's Ethernet packet
into the corresponding FDDI packet, which the router will understand.

This ONLY works with translating bridges -- not encapsulating bridges.

|>...
|>If routers are as fast as bridges why will some one use bridges?

Not all protocols can be routed.  Even if a protocol can be routed,
it takes less (usually no) network management to set up bridges, while
it always requires at least some network management to set up routers.
Those are some reasons why you might select bridges.

There are also reasons why you might prefer routers.  You have to 
consider the strong and weak points of each and see which ones are
important to your situation.  The list of strong and weak  points is
subject to change over time as technology evolves, but today there
is no "one best answer" and I would be surprised to see a single best
answer soon if ever.

|>...
|>I would like to have seperate measured filtering rates and forwarding rates
|>for bridges and routers.

For the DEC bridge the simple answer is "as fast as the wire can possibly
do it".  The actual numbers are in the datasheets, but if you know the
bitrates and minimum frame sizes you can compute them yourself...
(Those are measured rates.)

|>
|>Thank you for any pointers, I will summarize if I get any response.
|>
|>Regards
|>Nicolas Chrissakis                  Office: +30 81 229368, 229302,221171,229346
|>...


	paul