Ref: 10820003
Title: Communication Server Time Loss
Date: 3/7/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Users often ask why their Communications Servers (CSs) lose time.  Here is
the explanation.

There is no real time clock in the CS product line.  However, many
software messages that run on these units require a time stamp.  If
the software cannot figure out what time it is, it gets confused.  The
time stamp is usually picked up from the netmap packet transmitted by
the NCS.  But if no NCS is present on the network, this method does not
work.

If no NCS is present, a low-level TIC interrupt is taken from the
timer chip in the CS.  Because it is at a very low interrupt level, and
maskable, it is a very low-priority operation for the CS.  Any other
activity (especially on the Ethernet, the serial ports, or the disk drive)
when the timer chip sends out the TIC will cause it to be lost.  Gradually,
as more and more TICs get lost, the CS loses time.  (This is a general
explanation, because the Communications Servers vary in exact implementation
from model to model.)

Gateways and bridges may also lose time this way.  An IB running version
11000 or earlier may be a source of a time stamp.  If the IB time stamp is
incorrect, it will change the time in your Communication Servers to be
incorrect, also.

