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From: wyatt@cfa.UUCP (Bill Wyatt)
Newsgroups: net.dcom,net.lan
Subject: Re: Re: DELNI trees
Message-ID: <227@cfa.UUCP>
Date: Wed, 9-Jul-86 12:29:16 EDT
Article-I.D.: cfa.227
Posted: Wed Jul  9 12:29:16 1986
Date-Received: Fri, 11-Jul-86 06:33:44 EDT
References: <12250@amdcad.UUCP>
Organization: Harvard-Smithsonian Center for Astrophysics
Lines: 40
Xref: watmath net.dcom:2026 net.lan:1585

> 
> I may have missed something here but it doesn't seem to me that
> truncated preamble is a reason for limiting Connected DELNIs to one
> level.
> 
> Despite having just argued to the effect that a cascaded Connected
> DELNI should work, I would not recommend the use of such a
> configuration. There may be other reasons DEC does not support such a
> configuration.
> 
>>I have personally lashed up 3-deep connected DELNIs and it worked, but I
>>was lucky because all of the transceivers involved could deal with the
>>truncated preamble.
> 
> Yes, it may work at the time when you install it but the next time you
> expand the network, will it still work?
> 
> I must also confess to being confused by Bill's statement that
> "transceivers do not pass carrier sense through to an interface".
> Assuming he means a station when he says "interface", is not the
> presence of signal on Circuit DI (received data) of the AUI cable an
> indication of carrier? And what are the implications of this with
> regard to cascaded DELNIs?

All right! I give up. As I mentioned in the original posting, I was
passing along info from someone who was not himself an expert on 
the technical aspects of Ethernet, but had had it explained to him. 
Obviously, this third-hand info is not ideal, and I don't know how
what the real problem is. 

One thing that was definite: cascaded connected DELNIs are unstable- 
that is, they may work and then later cause massive problems when a network
expands.

Isn't there anyone out there, preferable the design engineer at DEC, who
*really* has the straight story?
-- 

Bill    UUCP:  {seismo|ihnp4}!harvard!talcott!cfa!wyatt
Wyatt   ARPA:  wyatt%cfa.UUCP@harvard.HARVARD.EDU