[c-nsp] ATM CRC errors

[Antonio Querubin]

On Wed, 27 Oct 2004, James Hamilton wrote:

> Hi there, we've got an ATM DS3 to Qwest (our telco) for Qwest based T1s and
> DSL.  It's taken ~588 input CRC errors in the last 20 minutes.  The count for
> the last week was ~140,000 CRC's.  I've been unable to match these CRC errors
> to the counters for my interfaces.  There were about 100,000 CRC's that I
> couldn't match to any interface except the main atm1/0 interface.
>
> We've checked the physical line, Qwest has monitored the port.  They are
> telling me that discarded cells are the cause.  If that is the case shouldn't
> I be able to match the main interface CRC counter to the CRC counters for all
> my subinterfaces?  Any insight would be appreciated.

I would think discarded cells would be an effect rather than a cause.

I recently had a similar issue between 2 ATM DS3 cards.  It turned out
both cards had timing problems and were replaced.  One thing that I
noticed while troubleshooting though is that if you set the ATM clock
timing to external on both ends, it can sometimes make the problem go
away.  A transmission guy later told me you can usually leave both ends of
a DS3 to recover clock from the line.