T3 Frame Type from ISP

[davidhuynh5]

I have a point to point T3 circuit from routerA to routerB. To the best of my knowledge, I understand that there are three different types of framing for the circuit (M13, Cbit, and Unframed). What are each framing type used for? What are the difference between the three? One of my T3 circuit used the Cbit framing type and it took thousands of input errors and carrier transistions per day. We tried everything under the sun to find a solution, but still could not figure out the problem. We contacted the provider and told them to change the circuit to unframed and the problem cleared! Very strange. Thanks in advance.

[Nagaraja Thanthry]

Hello,

The framing is generally used to send control signals either via inband or out-of-band. Here is a good document on framing for T1/T3 interfaces.

http://members.cox.net/michael.henderson/Papers/Framing.pdf

Here is a good document for troubleshooting T1/T3 issues.

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

Hope this helps.

Regards,

NT

[abaskara]

Adding to the earlier post, the framing setting needs to match on the directly connected segments of the network, to avoid framing related issues (link flaps, errors, etc). Sounds like there was a mismatch in framing with one of your telco devices (ADMs, etc), and hence setting it to unframed on both ends cleared the problem.

If there is a deadlock in troubleshooting these types of issues, you may get an analyzer (T-berd, etc), installed inline, and you will be able to see where the mismatch is.

Thanks,

Arun