IP Phone to IP Phone calls

Unanswered Question
Jul 11th, 2007

I have an issue mentioned below:

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.

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.

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

I have this problem too.
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jason-calbert_2 Wed, 07/11/2007 - 10:41

Try to ping from phones A's default gateway to phone B see if there is a delay in the network.

Also you could check to see if there is high CPU utilization that could be causing the problem.


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cscarindam14 Wed, 07/11/2007 - 10:46

Hello Jason,

Thanks for yours prompt reply. I would just like to mention again :

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.

cscarindam14 Wed, 07/11/2007 - 10:50

Yes Jason, all the phones are on the same LAN.

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.

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

mchandak Wed, 07/11/2007 - 10:57

If all the phones are local to the remote WAN, can you check the IP Address being shown for the Phones on CallManager when you search for the specific phones. Note that incase the IP Address being displayed on CCM Admin page does not match with the IP Address on the Phone, this could be the problem. When CM sends a message to the both the Phones to start Media exchange, it gives the IP Address as per the IPs Addresses that is shown on the CCM Admin page as the CM believes that is the IP. So if the CM has the phone registered using a NATed address and the phone would try to send audio to the NATed IP of the Phone and not the Local LAN IP Address.

cscarindam14 Wed, 07/11/2007 - 11:01

hi did you mean we can perform the steps mentioned by you when These are all Cisco IP phones, registered on Cisco Call Manager cluster and The phones reside on the same local area network,

mchandak Wed, 07/11/2007 - 11:04

From what I have understood, the Phones are local to one LAN and the CallManager is over WAN. Is that right ??

If the above is correct, can you check the IP Address being displayed when you do a search for this phone and confirm that the IP Address is the same as the phone assigned to the phone and not a NAT IP Address.

cscarindam14 Wed, 07/11/2007 - 11:08

yes you are right. the phones are local to one LAN and CAllManager is over WAN.

Alright I would check the steps mentioned by you and would let you know the results.

Let me know what if there is IP address mismatch. what needs to be done here?

Yours suggestions would be extreme helpful as you have got the scenario perfect.

cscarindam14 Wed, 07/11/2007 - 11:28

okay am going through it and will let you know if it has helped me to resolve the issue. Thanks a lot for your help. Will keep you posted.

cscarindam14 Wed, 07/11/2007 - 11:30

I see in the tac cc case as the title being marked as "The user experiences one-way audio on IP telephony calls when NAT is enabled"

But I am facing audio delay issues.

johnhsnow Wed, 07/11/2007 - 12:17

Yes , it doesnt sound like a NAT issue. To me it sounds more like a congestion issue and Qos tools need to be tweaked.

Does the delay occur right from the call setup process?

If there is delay once the call is setup ( across WAN to CCM )and also during session( RTP over LAN )then check the LAN. It could be so many number of things.

You running Auto Qos? Check your packet counters and Qos buffers and policy maps. Where are you marking your voice traffic? Any DSCP rewrites? Policing? Shaping ( causes delay )? Your DSCP<>CoS maps correct?

I think I would probably start capturing some sniffer traces to help you see more whats going on after checking your configuration perhaps.

Hope that gives you some things to consider.

cscarindam14 Wed, 07/11/2007 - 13:56

could you please throw more lights on your previous reply?

how to proceed step-by-step. Am bit confused

cscarindam14 Wed, 07/11/2007 - 12:03

This tac case collection deals with only one-way audio problems.

what are the other possibilities that audio delay occurs while placing calls from one IP phone to another IP phone in the same LAN

mchandak Wed, 07/11/2007 - 12:09

It all depends on how the setup is currently. Depending on the Audio patch and how and if NAT is configured and handled. I'd recommend checking the NAt recommendations and ensure that traffic does not actually go to the Internet and return. I'd personally say the best way to progress from here is to identify what IP CM is trying to use when asking the phones to send audio to and what is the IP Route between both the phones using the IP Address the CM is aware of

cscarindam14 Wed, 07/11/2007 - 12:20

so that suggests if there is IP address mismatch as stated by you in yours previous reply we would face audio delay issues while making calls from one iP phone to another ip phone in the same LAN

mchandak Wed, 07/11/2007 - 14:10

Well, as of now, its more like we are shooting in the dark. As of now, we dont know what is the Path being used for Audio between the 1 IP Phones. To start with the troubleshooting, I'd suggest first try and find out what the is the patch currently being used and see what is the delay being added with the path. Even with both the IP Phones being at the same physical LAN, if they are trying to reach each other using the NATed IP Address, then we need to look at the path taken by them. It could even be possible that the NATed patch is configured . We need to find out what IP Address CM believes is assigned to the Phones and do a traceroute to see what is the path.

Delay in Audio is more commonly caused due to the delay being introduced in the network.

Zin.Karzazi Wed, 07/11/2007 - 23:35

Your best bet is to start with a sniffer (ethereal) on both phones. Also see if you have any mismatch on your speed duplex setting (switch & IP-Phones).


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