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From: rauletta@gmuvax2.gmu.edu (R. J. Auletta)
Newsgroups: comp.dcom.lans
Subject: Ethernet Collisions
Keywords: What is the capacity of an ethernet? Is "this" normal?
Message-ID: <4150@gmuvax2.gmu.edu>
Date: 14 Apr 91 20:39:09 GMT
Organization: George Mason Univ., Fairfax, Va.
Lines: 52

We have been having some problems with an ethernet installation
that our Computer Network Services organization seems unwilling
to resolve. I am looking for some insight from those who might
have a sense of whether what we are seeing is normal.

The problem is characterized as follows.

1) Interactive sessions (typing etc) tends to get periodically
interrupted every couple of seconds for a tenth of a second or
more (the echo time becomes longer than the time to type a 5-10 character word.)
(This seems directly related to any burst of ethernet traffic
over about 10,000 bytes/sec as reported by etherd on a Sun.)
(When the ethernet load is low, the ethernet is very
responsive.)

2) The following indications on an American Network Connections
ANC-80 8-port fanout transceiver 802.3 while the problem is present.

RCV light intermittently active
REM COL blinks as the RCV goes out [everytime]. (Remote Collision)
LOC COL off
TRVR PRES light is dimly on.        (?)
SQE is off.

3) Traffic on the ethernet is (as reported by etherd on a
Sun workstation) about 25K-75K bytes per second running
about 50-150 packets per second when (1) is observed.
Most of the traffic is between just two Sun workstations.

4) Running netx (a tcp exerciser) on a Vax3600 to a VS2000
showing a network load of about 10% shows almost continuous collisions even
when only the two machines are active on the network.
(Every blink of the RCV light on the fanout unit results in the REM COL
blinking, the LOC COL stays off.)

Is this normal? At the described load would one expect to experience
poor interactive response that ethernets are known for? Might
this be due to the "supposed" problem with Sun's interpretation
of the ethernet standard in regards to back to back packets?

The general form of the ethernet is a thick riser with one thinnet
transceiver and several AUI transceivers with a bridge to
a fiber-optic segment.

What I am looking for are some suggestions as to what we might
look for to isolate the problem (such as "this sounds like a noise
problem", or "excessive reflections", or "load is just too high").

Characterized but still confused,

R J Auletta
rauletta@sitevax.gmu.edu