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Path: utzoo!dciem!nrcaero!pesnta!amd!rocksvax!dw
From: dw@rocksvax.UUCP (Don Wegeng)
Newsgroups: net.lan
Subject: Re: Stretching the Ethernet specs
Message-ID: <771@rocksvax.UUCP>
Date: Thu, 31-Jan-85 20:13:10 EST
Article-I.D.: rocksvax.771
Posted: Thu Jan 31 20:13:10 1985
Date-Received: Fri, 1-Feb-85 21:52:14 EST
References: <425@mcvax.UUCP>
Reply-To: dw@rocksvax.UUCP (Don Wegeng)
Organization: Xerox
Lines: 31
Summary: 

In article <425@mcvax.UUCP> jaap@mcvax.UUCP (Jaap Akkerhuis) writes:
>
>According to the Ethernet specification Versions 1.0 and 2.0:
>
>       "A maximum of two repeaters (or four half- repeaters, i.e. two remote
>	repeaters) may be in the signal path between any two transceivers on
>	the channel"

The reason that you are not suppose to use more than two repeaters is
that many of them drop up to 16 bits from the preamble while synchron-
izing to the timing, etc (you cannot predict the exact frequency of the
transmitter).  Therefore, if you had three repeaters in the path you
could possibly lose the entire preamble, therefore leaving nothing for
the receiver to sync it's timing from before the *real* data starts.

I suppose that somebody may manufacture a repeater that doesn't drop
as many bits.  If so then you ought to be able to connect more of
them into the net.  However, note that this would be in violation of
the Ethernet Version 2.0 spec (see page 83 for more details).  You'd
have to do some math to calculate the maximum length that a net can
be.


-- 
/Don

"Don't touch me, I'm a real live wire.  Psycho Killer..."

arpa: Wegeng.Henr@Xerox.ARPA
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