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From: dan@rna.UUCP (Dan Ts'o)
Newsgroups: net.lan
Subject: Ethernet Transceiver Cable question...
Message-ID: <326@rna.UUCP>
Date: Thu, 29-Nov-84 23:13:53 EST
Article-I.D.: rna.326
Posted: Thu Nov 29 23:13:53 1984
Date-Received: Sun, 2-Dec-84 05:18:54 EST
Organization: Rockefeller Neurobiology, NYC
Lines: 31

xyzzy

	Is there a minimum length for an Ethernet transceiver cable ?

	The scenerio is as follows. We have a VAX 780 and a VAX 750, each
with an Interlan Ethernet board connected to a DEC DELNI. The 750 has
the Interlan 10 foot flat transceiver cable connected to a 50 foot
round transceiver cable which connects to the DELNI. The 780, however,
only has the 10 foot flat transceiver cable connected to the DELNI, i.e.
no 50 foot transceiver cable. Operationally, the 750 looks fine, the
Carrier Sense and Collision Detect LEDs blink on and about once every
couple of seconds. (Probably rwho packets, etc. no users are using the
Ethernet). The 780, however, though mostly functional from the user
standpoint, has its CD and CS LEDs flashing wildly and occassionally
there are delays and even dropped connections at the user level.
	If I interpose a 50 foot transceiver cable in the 780's hookup,
every thing looks identical to the 750. Now, I imagine that the 780 with
the short cable is colliding with itself and retransmitting alot.
However a brief glance at the Ethernet specs shows no mention of a
minimum transceiver cable length. Is there one ? Or maybe just a property
of Interlan boards...
	Thanks.

					Cheers,
					Dan Ts'o
					Dept. Neurobiology
					Rockefeller Univ.
					1230 York Ave.
					NY, NY 10021
					212-570-7671
					...cmcl2!rna!dan