MGCP Gateway fast busy inbound calls outbound okay

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Hi all. Interesting issue here. I have a question about an issue we are having with our PRI gateways (MGCP 28XX). We've had the same problem on gateways at two different locations registered to two different clusters where inbound calls from the PSTN fail with a fast busy, but outbound calls work. When I do a debug isdn q931, I can see the inbound calls hitting the gateway. The only fix I have found is rebooting the gateway, often a couple of times, and resetting the gateway in Call manager.

I'm wondering if this is an IOS or gateway load issue, since it is happening in both locations on two different clusters; CM in one location is 4.x and the other is 5.x.

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Tommer Catlin Wed, 07/16/2008 - 10:18
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Did this just start or is this a new install?

If your MGCP packets are dropping you could be losing connectivity with CUCM. Check in your RTMT logs if you see gateways register drop or re-register.

ckltd7401 Wed, 07/16/2008 - 10:31
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Hi, we're having a situation in which the symptoms are much the same; fast busy on any incoming calls to DIDs and it's intermittent. I cannot see any registration issues in the logs and this problem just started today. Also, we are not seeing proof that the inbound calls get to the VGW when the intermittent outage occurs. Any info on this would be much appreciated.

Tommer Catlin Wed, 07/16/2008 - 10:45
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Have you checked the RTMT logs to see if the gateway is dropping registrations? Im assuming you are having network issues with MGCP packets dropping somewhere is what I think. Probably best to turn on debugging for MGCP at the routers and log it. But also keep an eye on CUCM clusters to see if they are struggling at all with processing, memory, etc. if they are peaking in utilization, they could be dropping calls, or delaying the call setup process

Tommer Catlin Wed, 07/16/2008 - 11:16
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Well, the phones would fall into SRST mode and still be able to dial no matter what. Inbound would be affected if you did not have voice tranlsation profiles setup

ckltd7401 Wed, 07/16/2008 - 11:07
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We found our issue to be with our Telco. We noticed that the dropped calls were happening with callers using certain cell carriers like Verizon. We called our Telco and they informed us that they were experiencing routing issues with certain cell carriers. That explains why we couldn't see the dropped calls hit our VGW.

Adrian Saavedra Wed, 07/16/2008 - 11:37
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Hi friends,

I saw this type of issue months ago. To help isolate the problem, as part of your troubleshooting steps, please check your Telco's channel select order and in your CallManager (if your gateway is using Bottom up or Top Down). If you're using the same order select as the Telco, it is possible you can experience call problems.


- Adrián.


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