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From: nraoaoc@nmt.edu (NRAO Array Operations Center)
Newsgroups: comp.dcom.lans
Subject: Re: Plugging repeater into DELNI: why not?
Message-ID: <1991Jan22.224925.1818@nmt.edu>
Date: 22 Jan 91 22:49:25 GMT
References: <1991Jan22.123047.397@arizona.edu>
Reply-To: rmilner@zia.aoc.nrao.edu (Ruth Milner)
Distribution: world,local
Organization: National Radio Astronomy Observatory, Socorro NM
Lines: 38

In article <1991Jan22.123047.397@arizona.edu> Leonard@Arizona.EDU writes:
>According to my trusty DEC _Telecommunications and Networks
>Buyer's Guide_ (Jul 90, p. A-14):
>
>  * A repeater cannot be connected to a DELNI.
>
>Is there any inherent limitation in a multiport transceiver
>that prevents repeaters from being plugged into them?  Or is
>this just some bogosity in the DELNI as built by DEC?
>
>Can 3rd party repeaters be plugged into DELNIs?  Can DEC
>DEREPs be plugged into 3rd party multiport transceivers?
>Can 3rd party repeaters plug into third party multiports?

A repeater cannot be plugged into a DELNI unless the DELNI is set up so that
it does not transmit heartbeat. The repeater, even DEC's own, will interpret
heartbeat as a collision.

If your DELNI is connected to an external Ethernet (the 9th connector), it
should not be transmitting heartbeat. If it is standalone, you will have to
get a loopback connector, and flip the little switch to external mode, to 
prevent this. This is what I was told by a DEC engineer at an "Advanced
Ethernet Concepts" tutorial. Since I have never tried it myself (in the one 
case where I actually had a DEMPR and a DELNI beside each other, I didn't want 
the DEMPR connected to the external network), I can only assume he knew what 
he was talking about :-). I know little about the DEREP, so I can't say for 
sure that it behaves like the DEMPR, but it ought to. The only differences
should be the media and the number of connections.

The "Buyer's Guide" is set up so that when anyone who reads it follows all the
rules, their network is guaranteed to work. A lot of the "don't" rules actually
only cover some situations; in other situations, the thing you are told not to 
do will work, but you have to know what you are doing, and you have to be 
prepared for it to not quite work right if you screw up :-) .
-- 
Ruth Milner
Systems Manager                     NRAO/VLA                    Socorro NM
                            rmilner@zia.aoc.nrao.edu