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From: leonard@arizona.edu (Aaron Leonard)
Newsgroups: comp.dcom.lans
Subject: Re: Plugging repeater into DELNI: why not?
Message-ID: <1991Jan23.143949.400@arizona.edu>
Date: 23 Jan 91 21:39:48 GMT
References: <1991Jan22.123047.397@arizona.edu> <1991Jan22.224925.1818@nmt.edu>
Organization: University of Arizona
Lines: 57

A consensus has emerged on why you can't plug a repeater into a DELNI.
The story goes something like this (thanks to Kevin Oberman, Cliff 
Frost, Steven Lendt, Wayne Sung, Chuck Kollars and Ruth Milner):

    1. A repeater must not be connected to a transceiver that
    generates SQE.

    2. A DELNI will issue SQE on all of its transceiver ports if it
    is in LOCAL mode, or if its AUI port is attached to a transceiver
    with SQE enabled.  (However, if the DELNI's AUI is attached to a
    non-SQE transceiver, or if the DELNI is in GLOBAL mode and has a
    loopback plug on the AUI, then it will not issue SQE.)

    3. DEC tells its customers that you shouldn't plug repeaters into
    DELNIs to avoid boggling their little minds (and their field
    servants' little etc.)

I do not believe this story for the following reasons:

    1. DEC insists that the DEREP *must* be connected to an H4000-A
    (heartbeating) transceiver, and *cannot* be connected to an H4005
    (non-SQE) transceiver.

    2. DEC says that the DEREN (its new repeater) can sense whether it
    is attached to a heartbeating transceiver or not, and configure
    itself accordingly.

    3. DEC has proven itself to be unafraid to publish baroque DELNI
    configuration guidelines, in its rules for hooking up DEMPRs
    to DELNIs (see _Telecom & Nets Buyer's Guide_ Jul 90 p. A-19.)
    The published rules for DEMPRs in fact jibe with the description
    above of how to get a DELNI not to issue heartbeat.

A more plausible hint (from Cliff Frost) is that DELNIs "strip
preamble".  The mechanics of precisely how this might impact 
repeaters is unclear and no doubt over my head.

Let me, then, propose some rules for hooking up repeaters to 
multiport transceivers, so that the more knowledgeable among you
might shoot them down:

    1. A DEREP can be plugged only into an H4000-A (or any other
    transceiver that offers heartbeat), but not into a non-SQE
    transceiver, or a DELNI, 'cause DEREPs are old and weird.

    2. A DEREN can be plugged into any available transceiver but not
    into DELNIs 'cause DELNIs are old and weird.

    3. No third-party repeater can be plugged into a DELNI 'cause
    DELNIs are etc.

    4. Any third-party repeater can be plugged into any non-SQE (802.3)
    transceiver or into any third-party multiport transceiver, as long
    as the multiport transceiver does not transmit SQE. 
    [This rule in particular I offer in order to draw flames.]

- Aaron