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From: mah@hpuviea.UUCP (Michael Haberler)
Newsgroups: comp.dcom.lans
Subject: Re: 802.3 and Ethernet on the same wire?
Message-ID: <860@hpuviea.UUCP>
Date: 19 Feb 89 14:42:23 GMT
References: <5379@videovax.tv.Tek.com>
Organization: Hewlett-Packard Vienna,Austria
Lines: 35

> What kinds of bad things can happen when 802.3 and Ethernet packets are
> present on the same piece of wire?  What are the hardware differences,
> if any, between 802.3 and Ethernet hardware?

Re: 802.3 vs. Ethernet packets: 
Should not be a problem, because they're easy to distinguish:

Ethernet packets have the layout
+------------------------------------------------------+
| dst adr | src adr | type field | data.......| crc-32 |
+------------------------------------------------------+
    6bytes   6bytes     2bytes       

IEEE802.3:
+------------------------------------------------------------------------+
| dst adr | src adr | length  | LLC data (SAP's)   | data.......| crc-32 |
+------------------------------------------------------------------------+
    6bytes   6bytes    2bytes       

So, as  no legal IEEE length consitutes a legal Ethernet type field ( types
start around 0x800), they can be distinguished by looking at the type/length
field value.

IEEE MAUs (aka transceivers) define additionial signals, like Jabber (inhibit
transmit of oversized packets). My experience is that one can use Ethernet
controllers with IEEE 802.3 MAUs but not vice versa.

-mah


-- 
Michael Haberler		mah@hpuviea.uucp 
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