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ISDN PRI Errors on a 3845 Voice Gateway using NFAS


I am not sure if this is the proper forum for this but I have a 3845 that I am using as a MGCP gateway; I currently have 2 PRI T1's configured in an NFAS group using the MGPC service. The problem I am seeing is that only the primary D channel T1 is showing up as "MULTIPLE_FRAME_ESTABLISHED" the backup D channel T1 is only showing up as "TEI_ASSIGNED".

Prior to issuing the "service mgcp" command to the pri-group for NFAS both T1's showed as "MULTIPLE_FRAME_ESTABLISHED" and everything looked fine but now I get the following q921 debug errors (see below) and have been unable to find anything related to the messages; but from the looks of it the switch is not offering a TEI assigment; if anyone could shed some light on this it would be appreciated.

Debug Message:

2:47:05: ISDN Se1/1:23 Q921: User RX <- SABMEp sapi=0 tei=0

2:47:05: ISDN Se1/1:23 **ERROR**: L2IF_SendPkt: idb is NULL

2:47:05: ISDN Se1/1:23 **ERROR**: process_rxdata:L2IF_SendPkt Failed

2:47:06: ISDN Se1/1:23 Q921: User RX <- SABMEp sapi=0 tei=0

2:47:06: ISDN Se1/1:23 **ERROR**: L2IF_SendPkt: idb is NULL

2:47:06: ISDN Se1/1:23 **ERROR**: process_rxdata:L2IF_SendPkt Failed

2:47:07: ISDN Se1/1:23 Q921: User RX <- SABMEp sapi=0 tei=0

2:47:07: ISDN Se1/1:23 **ERROR**: L2IF_SendPkt: idb is NULL

2:47:07: ISDN Se1/1:23 **ERROR**: process_rxdata:L2IF_SendPkt Failed

5 Replies 5


Unfortunately, NFAS in MGCP mode is not supported by Callmanager. You'll need to use H.323 if you want to keep NFAS.


" Use Media Gateway Control Protocol (MGCP) gateways for the PSTN if you do not require H.323 functionality. This practice simplifies the dial plan configuration. H.323 might be required to support specific functionality not offered with MGCP, such as support for Signaling System 7 (SS7) or Non-Facility Associated Signaling (NFAS). "

Thank you for the response.

Sorry to be the bearer of bad news.

What you're seeing is the GW want's to backhaul two D-Channels back to CCM. But you only have one Gateway configured in CCM, and there's only one active D-Channel anyway. CCM just doesn't know how to handle this. Hence the L3 failure.

Is there any strong requirement for NFAS? Seems to me you could use two normal PRI, with an ordered route-group/route-list combination that only uses the second(backup) when the first is full or down.

It is not really a matter of requirement; it comes down to the fact that I was expecting the Telco to provision two separate PRI's but when the Telco called to finish the provisioning I was told that the PRI's were configured using NFAS. The problem comes in because of time; I have to have these devices up within the next 2 weeks and in order for the Telco to change this from NFAS to two separate will take a complete re-provisioning of the circuits which will take another 30 days give or take.


Hopefully H.323 doesn't break your deployment model too much. And you can use it to buy some time until the carrier can cleanup its mess.

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