Tranceiver Question

[Jack Weldon]

In article <8912230716.aa07332 at SMOKE.BRL.MIL> XBR2D96D at DDATHD21.BITNET (Knobi der Rechnerschrat) writes:
> Can you please give a bit more information about that? What are the
>consequences when SQE is on (especially the 3100's)?
>
        At the physical layer, the only question is "heartbeat" or
not.  Ethernet version 1.0 has no heartbeat.  Ethernet version 2.0 has
heartbeat.  IEEE 802.3 has heartbeat.  The other differences at the
physical layer are minor.  The heartbeat is only between the controller
board and the transceiver or multiplexer box.  The ethernet cable
"knows" nothing about heartbeat.  The idea behind heartbeat it is to
make sure the collision line on the transceiver cable is connected up.
To quote the cabletron systems st500 manual, "at the end of each
transmission by the transceiver, it must send a short burst of 10MHz
waveform on the collision lead to permit the controller to check proper
operation of the collision signal path.  There is no collision test
signal when just receiving."  So everything is fine at this layer as
long as the controller and tranceiver agree on heartbeat.

What this means is that you can use either SQE, or no SQE--what matters is
that your transceiver and your Ethernet controller agree that it is on or off.
The 3000's Ethernet boards were shipped with SQE off, but can be modified to 
use SQE by your local field engineer, as necessary. I see no reason to do this
unless your particular type of transceiver supports ONLY SQE (rare, but I have
seen them...)

>A Merry Christmas and A Happy New Year 1990
>Martin Knoblauch

Thanks--You Too!!

Jack Weldon
SGI Product Support