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New Member

Input Errors Reported On Serial Interface

I'm trying to further troubleshoot a problem with a point-to-point T1 link. I have a T1 link that I am questioning the quality of, due to the input errors that have been reported on my serial interface at my end of this circuit. I first was using a 2610 with a external DSU (Tylink ONS-150) and a Cisco serial cable at each end. The DSUs were configured for B8ZS/ESF at full T1 speed, which was the confirmed provisioning of the circuit. The router at my end reported input errors, which I believe were coming from the circuit. To make a long story short, I've since replaced both routers at each end, the external DSUs and cables. After doing so, the problem still existed. According to the circuit provider, they see a clean circuit end-to-end as per their testing. After that, the only other option we thought of was eliminating the external DSUs altogether and replace them with internal WIC T1 interfaces. After 3 days on the new WIC interfaces, the problem still exists. This is now using new routers, new WIC T1, and verifying wiring at both ends. Am I losing my mind, or is this circuit dirty? Thanks!

New Member

Re: Input Errors Reported On Serial Interface

You have no idea how many times I've fought this battle with telcos! They're amazing, aren't they?

A few things to check:

If you have an extended DMARC, verify that the signal is good to your CSU. Telco engineers *can* do this with their equipment, but may balk since its not *their* cabling.

Have them replace the smartjack. I've seen these things go bad many times. I've even had the chassis go bad that the smartjack resides in.

Do loopback tests with the telco.

Have them loop from the CO back to the device that receives the errors. If you still get errors, an onsite telco engineer can loop from the smartjack back to the CSU. If you still get the errors, loop your internal wiring back to the CSU. You see where this is going...

Good luck... this part of the job sucks! :)


New Member

Re: Input Errors Reported On Serial Interface

I agree with Mick, i't tough to get the Telcos to work the problem. You might try changing encapsulation on the serial interface on both ends. If its HDLC go to PPP or the other way around. Also we have experienced many issues with telco clocking.

Depending on the provisioning, the telco may or may not be providing timing. You can look at the T1 controller on the WIC card. Are you seeing errors there? If so, it's a safe bet that there are circuit or cable problems.

The way we prove which side the problem is on is to place a cable loopback at the end of our cable at the demark. Of course this will bring the circuit down, but if the errors stop, it will show the problem is on the telco side.

New Member

Re: Input Errors Reported On Serial Interface

Important note about loobacks that I forgot to mention.

If you put your CSU/DSU into loopback (back to the router) and you're using HDLC encap on the router, your interface will go UP/UP. This is really helpful since it will send data and errors will continue if there's a problem. You can't do this with frame or ppp.

Also, I forgot to ask what kind of errors you were getting. Are you sure that telco is providing the clocking? Sometimes they don't. Try changing your encoding to AMI/SF just for giggles.

Hope that helps