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From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: 3 Protocol Query
Message-ID: <6427@ucbvax.ARPA>
Date: Tue, 23-Apr-85 02:18:39 EST
Article-I.D.: ucbvax.6427
Posted: Tue Apr 23 02:18:39 1985
Date-Received: Wed, 24-Apr-85 02:18:29 EST
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Organization: University of California at Berkeley
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From: nbires!mccallum@BERKELEY (Doug McCallum)

	>comes with the new ethernet ieee standard for packet format. under the
	>old 802.2 you have 6 bytes of destination ether address, 6 bytes of source
	>ether address and a 2 byte type code. under the new 802.3, you have
	>the 12 bytes of address, followed by two bytes of length information.
	>there is a type field somewhere, but it means all the protocols will have
Don't confuse 802.2 with being an old version of 802.3.  IEEE standard 802.2
specifies a Logical Link Protocol to be used with the 802 family of access
methods.  802.3 describes a media access method (CSMA/CD).  Ethernet
Versions 1.0 and 2.0 specify 6 bytes destination address, 6 bytes source
address and 2 bytes of type.  IEEE 802.3 specifies 6 bytes of destination,
6 bytes of source and 2 bytes of length.  XEROX has reserved all valid IEEE
lengths as IEEE  specific types.  It is possible to mix both versions on a
given network.  If the 802.2 protocol is not used with an 802.3 network, you
have an ethernet version 2.0 type network.  As an example, the IP type value
for ethernet is 800(hex).  This value does not correspond to a valid IEEE 
length.  If the value in the type field (length field) corresponds to a valid
IEEE length, then an IEEE 802.2 header comes next and can be distinguished
from an IP field.

	>to have the transport layer changed, and it isn't possible to run both
	>protocols on the same wire. so much for standards ....
The transport layer would need no changes, just the link layer and then it
isn't that much of a change.

			Doug McCallum
			NBI, Inc.
			{attunix, ucbvax, ut-sally, hao}!nbires!mccallum