Isdn-Pri B-channels in lockout

Unanswered Question
Oct 9th, 2007

I have a location with (2) 3825 routers running IOS version 12.4.13d. There are two ISDN-PRI DMS-100 circuits in one router and a third in the second router. We are having issues with the location not getting incoming calls and the telco is telling me that the b-channels keep getting locked out. They have asked me to find out if I have b-channel service messaging enabled on my system. The DMS-100 switch is DMS-100 version LEC17 according to the telco. Has anyone seen this before? Any help would be appreciated.

I have this problem too.
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Paolo Bevilacqua Tue, 10/09/2007 - 12:54

In theory is possible that B channels are locked on a DMS-100 switch type, but the router would not initiate that without an user command.

I suggest you upgrade to latest 12.4 in order to obtain all the ISDN bugs fixes.

Then if the problem happens again, send here output of show isdn status and "term mon" with "debug isdn q931". In fact, if the problem is happening right now, send it here.

Paolo Bevilacqua Tue, 10/09/2007 - 14:00

Nice trace. We can observe two anomalies:

1st, for incoming calls, router is sending a notify message that the switch rejects. More on this later.

2nd, about the "channel service" issue, we see that the switch is repeatedly telling to the router, that chans 1 and 23 are back in service, thing that the router acknowledges.

Now, apparently the router has never told the switch that any channel were to be put out of service, so the question should rather made to to telco, why are you reporting these messages? And why only channels 1 and 23 ?

A little more about the notify message. it just shows how Cisco and Nortel have different opinion about the implementation of the "dms-100 protocol". It should not be serious and not related to the problem mentioned.

Action need to your side anyway, upgrade to 12.4(17) and see if it happens again.

rgoodwin7399 Tue, 10/09/2007 - 14:12

Thanks so much for the information. I will try the ios upgrade and see if it helps. I have found out that apparently dms-100 switches by default have b-channel service messaging enabled even though most phone system manufacturer's do not support these messages and it causes the issues I am having. Still waiting on confirmation about these messages from Cisco tac and telco. This is a very interesting thread between two phone company guys.

I will repost once this is resolved so anyone else having this issue might be able to get is fixed faster.

rgoodwin7399 Wed, 10/10/2007 - 05:57

Thanks for the link. I don't see the 3800 or 2800 platform mentioned as supporting this feature in the document you provided. Does it apply to those platforms as well?

Paolo Bevilacqua Wed, 10/10/2007 - 06:28


the doc is pre-existing to these platforms, so yes. But worry not, have the service messages removed from the switch and you should be fine.

I loved the part about a large telecom vendor pbx and switch guys blame each other in a conf call :)

rgoodwin7399 Wed, 10/10/2007 - 06:31

Yeah that was pretty good to me as well. I will have the telco turn them off on their end and I should be good to go. Do I need to turn them off in the router as well? I haven't had time to read the doc yet so if it is in there I will know shortly.


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