Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!ucbvax!hplabs!hpda!hpcupt1!hprnd!pat
From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.dcom.lans
Subject: Re: Does the EtherSwitch eat preamble?
Message-ID: <2230109@hprnd.HP.COM>
Date: 29 Aug 90 16:27:36 GMT
References: <1990Aug27.143144.62@arizona.edu>
Organization: HP Roseville Networks Division
Lines: 31

> 
> The next question is, does the EtherSwitch act like a repeater and
> gobble preamble (so that you are limited to a max of 3 in series),
> ----------
> 
Repeaters as defined in ANSI/IEEE Std 802.3c-1985 do not gobble
preamble.  They are required to transmit a full preamble (7 bytes
of preamble followed by a byte of Start of Frame Delimiter).  Not
transmitting a full preamble can cause a false collision detect on
coax due to analog details of coax segments and collision detect
methods.

The original Ethernet and IEEE 802.3 repeater definitions did not
include this requirement.  The original IEEE 802.3 repeater
definition did include the note: "The fundamental concepts in the
section are essentially correct, however, additional statements
may be needed for a complete specification."  The ISO publication
of the same strengthened the note to: "Section 9 (Repeater Unit) of
this standard is undergoing revision.  DIS 8802-3/DAD 3 is intended
to replace Section 9 and represents a substantial revision."  

ANSI/IEEE Std 802.3c-1985 has been published by IEEE in the
_802.3_Supplements_.  Since it has completed the ISO approval
process, it will be published in ISO 8802-3 ANSI/IEEE Std 802.3,
Second Edition replacing the original section 9.  (This  
is expected to be in publication within a couple of months.)

The repeater limit (4 according to 8.6.1 and 10.7.1 of IEEE 802.3)
is based on round trip delay and on interpacket gap shrinkage.

Pat Thaler