[c-nsp] E1 controller - clock problems with 'line' fine with 'internal'

[Masood Ahmad Shah]

Circuits from the SAME carrier can generally share a clock because the
carrier will generally have a single "clock source" for all their circuits.
If you have 3 E1 from the same carrier, on one of the E1's you would
configure "clock source primary" and the rest could be "clock source
internal", because the internal clock would be synced to the "primary" line.
You can also configure each interface as "clock source line" which is the
default. All E1's need a clock source, either your end or their end, and if
this is a carrier circuit, than they provide the clock and you need either
"clock source line" or "clock source primary" on one E1, and "clock source
internal" on the others.

Regards,
Masood Ahmad Shah
Nexlinx
BLOG: http://www.weblogs.com.pk/jahil/



-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ras
Sent: Wednesday, August 22, 2007 5:14 PM
To: c-nsp
Subject: [c-nsp] E1 controller - clock problems with 'line' fine with
'internal'

I've recently run into a slightly strange problem with one of my E1
circuits.

We operate a hub-and-spoke setup, where a number of lines terminate into a
single aggregation router on our side, and into a bunch of different
locations/CPEs on the remote end.

For all these lines, we have always had 'clock source line' for the E1
controller on both the aggregation router and the CPE routers. This has
worked fine and the controllers show no errors.

I've just commissioned a new line into the same aggregation router, exactly
the same equipment on the CPE side (2811, VWIC2-1MFT-G703), exactly the same
equipment on PE side (2811, VWIC2-2MFT-G703). But this time, we were seeing
continuous 'Slip Secs' (top marks to whoever made that term up
incidentally), which were also showing up as 'Errored Secs' (but crucially,
never 'Errored Secs').

After much investigation and a VWIC/chassis swap later, we were in exactly
the same position.

I think tried configuring the aggregation controller (just for that one
port) with 'clock source internal' and bang all the errors disappeared
completely. It's now been running well over 48h without a single errored
second, versus 1 second per second before.

For reference, the aggregation router now has:
controller E1 0/0/1
 framing NO-CRC4
 clock source internal
 channel-group 0 timeslots 1-31

and the CPE has:
controller E1 0/1/0
 framing NO-CRC4
 channel-group 0 timeslots 1-31


Has anyone seen anything like this before and/or know what might cause this?
My telco insists that they've tested the circuit end to end and it's working
as expected (and to be fair, it is now..)

Thanks,
Ras
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