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From: mitton@enet.dec.com (Dave Mitton)
Newsgroups: comp.dcom.lans
Subject: Re: TR,FDDI,Ethernet
Message-ID: <22823@shlump.lkg.dec.com>
Date: 22 May 91 00:55:26 GMT
References: <1991Apr25.190253.7416@dit.upm.es> <1991Apr25.191715.7567@dit.upm.es>
Sender: newsdaemon@shlump.lkg.dec.com
Reply-To: mitton@enet.dec.com (Dave Mitton)
Organization: Digital Equipment Corporation, Littleton MA
Lines: 47

>From: churti@greco.dit.upm.es (Francisco Gutierrez de Churtichaga)
>Newsgroups: comp.dcom.lans
>Subject: TR,FDDI,Ethernet
>Date: 25 Apr 91 19:17:15 GMT
>Reply-To: churti@greco.UUCP (Francisco Gutierrez de Churtichaga)

>
>1)    Does the SRT bridging pseudostandard in fact allow interoperability 
>      between a TR and a Ethernet END station or does it only provide the 
>      means for sharing a internetwork structure (ie bridges)?.

SRT is a specification under development.  It will become a standard when
(or if) it is approved.
It helps TR/Ethernet internetworking in that it propagates Transparent Bridging
into the Token Ring environment, and removes the need for Source Routing
support (both in code and wire overhead).

However, SRT does not solve some the other TR to Ethernet interoperability
problems, such as; bit order in MAC addresses, Functional Address to Multicast
mapping, 802.2 to Ethernet frame format translation, or long packet
segmentation.  You have to evaluate the protocols on your LAN and whether
_they_ support cross-media bridging.

>2)   Should the answer to the question above be negative (that is,communicating
>      TR end stations and Ethernet end stations across an SRT bridge is
>      impossible), what should be done to get this done?

Communication is not impossible.  There are just all of these problems
that need to be avoided.  It's conceivable to build a bridge that solves 
them, but so far every major token ring protocol implementation has blundered 
in some different way, and such a bridge will have a polyglut of protocol 
parsers and fixups.  Typically protocol independance has been bridges 
primary feature that gains them their performance.

The cynical consider Routers to be the only sane solution.

>3)    Has anyone had experiences communications diverse environments across
>      an FDDI ring?. If so, what kind of equipment have you used?, have you 
>      had problems integrating a concentrator, say from ATT and a CISCO 
>      FDDI bridge using a Single Attach connection...Any comments regarding
>      these or similar matters would be very appreciated.

Digital produces an FDDI to Ethernet Bridge that you may want to look at.

	Dave Mitton,
	Token Ring Program
	Digital Equipment Corp.