Showing results for 
Search instead for 
Did you mean: 


Comcast PRI layer 1 deactivated

Last night we attempted to migrate from a Verizon PRI to a Comcast PRI.   Connecting to a 3925.


Both services are identical from a configuration point of view.

Both are NI2

Both are ESF

Both are B8ZS

Both are hdlc encap

Both have D Channel on the 24th timeslot.


The biggest difference is that I use a straight through cable on Verizon and I am supposed to use a cross-over cable with Comcast.   No worries, built and tested two of them on site.

When I connect straight through, I get nada.   When I connect with a crossover, the circuit comes up for up to 60 seconds and then goes down and after that has non-stop up/downs that last less than a second.   Same on both crossover cables. 


Unplug the 3925 end and plug in the loopback plug and Comcast is happy.   Put it back in the router and we return to the problems.   Unplug from the Comcast Adtran and plug in the loopback and my router goes green and is happy.   So both sides test out fine as does the cable.   Put it all together and I get nothing.   Unplug the cable and plug in the Verizon cable to the port and I go green with no errors.


I've proven that no single part seems to be bad, but I can't determine any way to get this up and stable.

On the few occasions that we were up for 30-60 seconds, we established on layer 2 and layer 3 just fine, but then we crash and burn again.   I'm not even getting far enough on the establishment most of the time to get an Q921 debug information because my issues are layer 1.  


Anybody have any ideas because I'm fresh out.   Cisco and my business partner that we use neither one had any ideas beyond what we had already tried.


The only thing I can think of is to check to make sure you have the right pin out for a PRI crossover cable, not a regular Ethernet crossover.

We double checked the pin-out last night with Comcast. And if I didn't have it right, the cross-over plug I have wouldn't work.

What's the pinout ? 1,2,4,5 cross-overed ? Other than that if the loopback works then it isn't an issue with the router and things were working with Verizon earlier so what changed is just the circuit. Can you send over the q921 log ?

Nipun Singh Raghav
"We cannot solve our problems with the same thinking we used when we created them"

There are no q921 logs.   Later in the process last night, we weren't able to get layer one to activate and that is when I turned on the logs.   No layer 2, no q921 log information.


And yes, the 1 to 4, 2 to 5, 4 to 1 and 5 to 2 cable.  


I agree with you that this appears to be a comcast issue other than if we put the loopback on the cable facing them, they go all green as well.   I can literally prove that everything works, but it doesn't.





Content for Community-Ad