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ISDN Call Dropping



I have a problem with a router with 4 ISDN PRI links for incoming VoIP calls. The problem that I am facing is that in a day, my ISDN status flaps between 'Multiple_Frame_Established' status to 'TEI_Assigned'. This happens once or twice in a day. I have two service providers and I am facing the problem on both the SP links.

The CPU utilization of the router for 2 processes is high. Could this be a reason for ISDN Flapping. If yes, how can I reduce the CPU utilization for the processes.








Re: ISDN Call Dropping

Hi there,

I had a look at the show tech and all seems ok, but the processor on that sort of load should be no where near what it is!!

I had a look on your software revision and it's a bug I'm afraid. Have a look at this link for more details:-


Headline: RTP: invalid RTCP packet may cause CPUHOG in VOIP_RTCP

There seem to be one or two issues with the VOIP_RTCP in that revision of code.

However, it's affecting quite a lot of versions of the 12.4 code (if not all of them) and is currently at a Severity 1 in the bug tool - which is as bad as it gets, but they'll be working hard to get a fix.

I'd suggest raising this with TAC so that they can advise you on the best steps to take or the version of code that would fix the issues - it might even be worth dropping down to 12.3(14). Raise it with TAC - they'll give you the best advice here.

Hope this helps,


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