Inbound calls fail PRI terminated on AS5400 with mica modem

[aaronmcquaid]

Hello TDM people (I hope some of you are still on this board.)

I have a legacy application that uses a Cisco AS5400 with a mica modem bank. I need to migrate it from a Sprint PRI to a Level 3 PRI. I attempted to cut over last night but it failed. We were getting fast Busy for the inbound test calls. I had Level 3 send the same DNIS as sprint was sending. So this means that my router config is identical when I test with Sprint and Level 3. The only change was when I would swap the cable back and forth between Level 3 and Sprint. Sprint worked and Level 3 gave me a fast busy every time. 

Level 3 told me that they were seeing a "release" from my router in their CDR. 

I have attached my config and debug isdn q921 det and debug isdn q931 detail which illustrates a working call on sprint and a failed call on Level 3. I hope that one of you can help to interpret the debug out put for me. Thanks in advance. 

[Joe Vallender]

From the failed call debug, it appears the B-channels are not staying up, therefore no channels are available for a call.  Question is why aren't the B-channels staying active?

[aaronmcquaid]

Hello Joe,

Thanks for your reply. Are these messages the ones that tell you the B channels are going down:

Aug 30 23:23:39.550 CDT: ISDN Se7/0:23 Q931d: CC_CHAN_ReleaseChanpri: channel 1
Aug 30 23:23:39.550 CDT: ISDN Se7/0:23 Q931d: CC_CHAN_ReleaseChanpri: channel 2
Aug 30 23:23:39.550 CDT: ISDN Se7/0:23 Q931d: CC_CHAN_ReleaseChanpri: channel 3
Aug 30 23:23:39.550 CDT: ISDN Se7/0:23 Q931d: CC_CHAN_ReleaseChanpri: channel 4
Aug 30 23:23:39.550 CDT: ISDN Se7/0:23 Q931d: CC_CHAN_ReleaseChanpri: channel 5

So you are saying that because there are no B channels the call setup request is ignored and that is what this message means:

Aug 30 23:23:30.866 CDT: ISDN Se7/0:23 Q931d: L3_Go: L3_GetUser_NLCB returned NULL cid 0x0 cr 0x801F ev 0x5 ces 1 -- Message ignored

Just want to be clear that I understand before going back to the ISP. 

[Joe Vallender]

Yes, those messages showing the B-channels being released indicate they are not stable/active, and it is repetitive.  Your support partner for your AS5400 may be able to interpret these messages and assist your ISP in resolving the instability.

[aaronmcquaid]

So I had a second window with the ISP. We removed the NFAS config and replaced it with:

pri-group timeslot 1-24

This seems to make it work. I have no clue why it works doesn't work with NFAS but works without NFAS. Any thoughts?

[Joe Vallender]

NFAS (Non-Facility Associated Signalling) is for when you have multiple PRI's sharing a single D-channel for signalling, freeing up the other D-channels for use as B-channels.  Having this setting active on your PRI might be confusing your ISP side or within the AS5400, causing the problem.  This assumes you do NOT have multiple PRI's with your ISP.

[aaronmcquaid]

We ordered 2 PRI with NFAS. The ISP was specifically made aware of that. The idea was to have a backup D channel. In the past, they had 5 PRIs with NFAS but the demand doesn't justify that anymore. 

It seems that this is some sort of compatibility problem with Cisco and the ISP or the ISP has some setting screwed up.