sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's CRC Errors

We are in the process of moving equipment from a SBC DS1 Private Line to a AT&T Private Line. SBC is moving all Private Line customers to the AT&T network. All runs fine on the SBC Line and when we switch over to the AT&T Line the far end Adtran CSU shows CRC errors. The application hardware (router, etc.) does however, run fine. AT&T has tested the line and says all is ok - the problem must be in the customer equipment. Any thoughts would be appreciated - thanks.

Pick one:


A. If it ain't broke don't fix it.
B. Find a bigger fish to fry.
C. Leave well enough alone.
D. Don't mess it up.
E. All of the above

P.S. What is the correct spelling of "Fuggedaboutit!"

I don't see how you can be getting true CRC errors and have no problems. How many? How often? And is that the only errors you see?

If I remember correctly, CRC errors are in the physical layer and should not be ignored. Might be a bad patch cable from the dmarc to the CPE at the z end? You may be able to pass data traffic on the line with CRC errors but you will probably see some latency. If they get bad enough, it can effectively take the data path down.

In my book, a clean circuit is just that. Anything else is not good and just comes back to bite you in the ass later.

CRC stands for cyclic redundancy check. It is a type of check sum that is added to the data stream. It works like a parity bit in serial communications, but is a little more sophisticated mathematically than that. According to Wikipedia, “a cyclic redundancy check (CRC) is …. particularly good at detecting common errors caused by noise in transmission channels.”

Well a little noise is normal. Not desirable but normal and expected in the real world. Ben Franklin said “be not disturbed at trifles or at accidents common and unavoidable”.

Unless your WAN link is slower than expected, I would not concern myself with CRC errors. If you didn’t have them before, then you had a very clean line. If you want to, you can do a speed check on your line. Here is one speed test site:
https://myspeed.visualware.com/

Well said

CRC errors are going to cause issues when dealing with Data, you may not have any voice issues, but you will start to see trouble when using a modem or a fax.

Double check your settings making sure you are set for B8ZS. Having any a point in the ckt set as AMI can cause CRC's. If so, have your carrier retest the ckt and make sure they run an "all zero's" pattern when they test. If any point in the ckt is not set for B8ZS "all zero's" will fail. Too often all the test patterns are not run when a ckt is tested. A tester will loop the NIU run one test pattern and beleive the ckt is fine when it's not.
And double check all connections and cables. These can cause crc's also.

I'll 2nd what SST is saying. Have AT&T loop the CSUs on each and and have them run an All 0's test pattern.

I worked for local telco, when we saw this issue it was the DAC's not programmed for B8ZS. Have telco check any mux's also..
good luck...