VoiP calls coming in over E1 do not work

Unanswered Question
Sep 16th, 2007
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I have noticed a strange problem with our IPCC Call Centre. There are 4 E1 PRI per Voice gateways, connected formerly via MGCP to a CCM Cluster. The calls are coming in and are connected, but the caller hears only a dump ringback, or just something like a dead connection. The calls go to an CTI route point in the CCM, which points to the IPCC.

Phone->Voip PBX -> ISDN by COLT-> Cisco VG2821 -> CCM->IPCC

We are not able to reproduce the error by calling via mobile, Cisco Phones or any other not SIP phone.

I have checked all ISDN q931 logs and the calls show up as connected until the caller hangs up, but he is not able to hear anything.

I have also noticed, that if I call in via my SIP provider for testing my call is disconnected. So this could by a problem of my SIP provider, but I'm not sure. We will now try if he is able to call a normal phone number, that does not go to IPCC.

Has anyone ever noticed such a behavior?

Many thanks in advance

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