Audio Delay issue while making calls between IP Phones

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Jul 11th, 2007
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I have an issue which is mentioned below in details:

ALl Cisco IP phones registered on Cisco Call Manager cluster.

The phones reside on the same local area network,The LAN is a complete Cisco architecture, Layer 3 routing.

The Phones are within the same CCM Region, and assigned with the same Calling Search Space.

If a users on Phone A (ext. 1237) calls a user on Phone B (1238) the connection establishes, however the audio is delayed 6 -10 seconds, in both directions.

The CCM Cluster is located across the WAN, with all the appropriate QOS supporting the IP Phone signalling. There are no VoIP call connections cross the WAN, the voice is all local, calls to and from the PSTN are via the local 3825 router.

Only calls between IP phone to IP phone have the audio delay issue, if any of the local IP phones receives or connects a call via the voice gateway, there is no audio delay.

Additional details:

The Cisco Call Manager service is on version 4.1 (3)sr5b - hardware is MSC-7835 H1

IP phones loads are:

7960, P00308000500

7940, P00308000500

7912, CP7912080003SCCP070409A

I would be grateful if someone could help me in this issue

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AJAZ NAWAZ Wed, 07/11/2007 - 12:33
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Have you tried just pinging around to see what the round trip delay might be?

cscarindam14 Wed, 07/11/2007 - 12:41
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nope i didnt try yet.

Could you please provide me with the relevant troubleshooting steps

jason-calbert_2 Wed, 07/11/2007 - 12:53
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The first troubleshooting step that you need to try is to ping the callmanager server from the side of the wan were the phones reside. Please post the round trip time.

You also can put a sniffer on the phone so you can see the RTP packets and messages from callmanager.

Please ping side of WAN were phones reside to the callmanager


johnhsnow Wed, 07/11/2007 - 13:05
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Just a thought here but I think if just rely on ICMP packets I dont think you will get Qos treatment on IP/UDP/RTP packets. This might not give you an accurate RTT because you are missing the RTP overhead.

cscarindam14 Wed, 07/11/2007 - 13:19
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so how do you want me to proceed? this is quite critical which needs to be resolved asap

johnhsnow Wed, 07/11/2007 - 13:56
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My suggestion is to start checking your interfaces ( IOS - sh interface CatOS sh port or sh counters )for packet/buffer drops and interface /link congestion > including WAN interface especially since that will be your slowest link.

ALso, I guess you could perform some ping tests as Jason mentioned to give you a general idea of RTT to rule out any major issues there and lets see if the interfaces are oversubscribed. You could SPAN the interfaces to get an idea of what other traffic is traversing the same interfaces.

cscarindam14 Wed, 07/11/2007 - 14:01
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thanks for all of yours help. I am trying to narrow down the issue.

Do you think it could be QOS issue as am facing with audio delay only when placing calls between one IP phone to another IP phone residing on the same LAN, however I dont face any issues while I place/ receive calls across the voice gateway

johnhsnow Wed, 07/11/2007 - 14:14
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I need more clarification when you say placing calls on the LAN. I understand that a call still needs to be treated by the ccm manager process regardless unless the gateway is an SRST router you are referring to?

If that is the case then you are not traversing the WAN. To me this would support a QoS problem still. 6-10 seconds is more than just delay - there is something seriously wrong in the network in this case and could be a compound problem.

A VOIP call should be between 150-200 ms.

A better understanding of your call flow might help me.

Is it similar to this ? Could you show us?

CCM>Distribution Layer<>Access layer<>IP Phone.


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