atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking Looped T1 - errors incrementing

I am new to this board and new to a position managing a small team of Network Engineers.

We’ve had an issue turning up a pair of T1s between our local and remote site. We’re having difficulty determining where and what the problem is.

The routers (Cisco 2621XM with internal CSU WIC) have their error counters (CRC, frame, aborts, interface resets) increment periodically. One interface will increment by thousands on a predictable basis (Tuesday and Friday mornings at 0000 - 0030).

The local router, WIC and cable to the patch panel have all been replaced, so we’re pretty confident that it’s not a customer (us) hardware issue. We’ve had the router configurations reviewed and they’re OK.

Our circuits are delivered to us in a patch panel in our network room. The smartjack is in our provider’s area and we cannot physically access or test the device.

We scheduled testing with our provider this morning (Friday – when a predictable error would occur). We had a hard loopback cable plugged into our local patch panel port. While “looped,” the errors on our remote router slowly incremented steadily (a few per minute). During the provider’s testing (I don’t know what tests), the error counters incremented over 1 million then slowed to the steady incrementing when the testing stopped. When we took the loop out this morning, the errors went back to periodic incrementing.

When we looped (line) at the remote router, our local interface began to increment steadily (a few per minute). When we unconfigured the remote loop, the errors went back to periodic incrementing.

My initial question is, would looping a circuit cause the errors? I would assume that looping a clean line would not inject errors.

Our provider says the line is clean.

Thanks in advance!

No looping will not cause errors. However if you had a hard loop not going through a CSU and a long circuit then you could get errors on testing. Testing to a looped CSU or NIC regenerates the signal, which is the way it should be tested if not doing head to head testing.

We had a similar post in Networking. Depending on which WIC card you have you may have end to end testing capabilities. I'm not familiar with this product only the information I've taken from Cisco's WEB site. You will be better off just testing the T-1 instead of going through all your other stuff to try to isolate where the problem is. You should have access to the 8pin jack on the back of the smart jack as that is your interface.

The errors you were seeing on your equipment while the phone company was testing could be caused by a lot of things, it wouldn't be a valid result in my opinion.

This should be your key! Get access to the telco areas. There are older facilities still out there that receive power locally instead of being line powered. Eliminate this as a possibility.

WearyTraveler -

Loop the CSU at the router. Check for errors. If you do not get any errors loop the CSU @ the smartjack, this will test your extended DMARC (layer 1). If you are getting errors at step 1 it is your WIC. If you are getting errors at step 2 it is probably your cable. A telcom T1 only uses 1-2, 4-5 which if you are using a 568B patch cable is usually the ORG and BLU pairs. If you are lazy like me cut the end off and use the GRN and BRN pairs (I will sometimes do this to run 2 T1s).

Run these tests and let us know.

Cisco's got a document that reasonably explains the various errors one might see on a T1/E1 interface. Not as practical as the advice given here, but it's a good reference to have none-the-less.

https://www.cisco.com/en/US/tech/tk713/tk628/technologies_tech_note09186a00800a758d.shtml

You guys are very helpful! Thanks - I will check these out.

This is what confuses me about the Cisco site. These are all DS0 terms, not T-1. So are they talking about the channels or the T-1? Why would they not use the same verbiage that's been used for decades? T-1 is T-1 and DS0 is DS0 and the two are no where near the same.

DTE = data terminal equipment

CD = Carrier Detect

CSU = channel service unit

DSU = digital service unit

DCE = data circuit-terminating equipment

CTS = clear-to-send

DSR = data-set ready

Bill -

This is exactly what I found in the Cisco VOIP classes.

Cisco is attempting to rewrite communications "in their own image". Why use terminology that's been around and tried and true for 40 years and more? Then Telephone people will be required (or available) to work on your equipment.

If you use "Cisco Speak" to describe something then only Cisco people can understand you or work on your equipment.

Not that I'm paranoid or a conspiracy theorist, but.....


Sam

Thanks for that Sam, I thought it was just me. As a pure phone guy it makes it hard to help the good folks that come around with these questions when a company isn't talking Telco language.

It makes for more robust communications via enterprise platforms while conversing by analog transmission that is digitized after being inputed to the handset.