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Codec issue with ICT and IP-IVR


i have a setup as follows:

[remote branch]---G.729---[clusterB CCM-B]---ICT----[clusterA CCM-A]---LAN----IPIVR

I have two clusters of CCM, Cluster A and Cluster B connected using ICT (non-gatekeeper controlled). In cluster A, there is an IPIVR using G.711 codec, configured in the same "region" as CCM-A.

A remote branch IP Phone at Cluster B registers to the Cluster B CCM-B. This remote branch uses G.729. When the remote branch IP Phone tries to reach the IPIVR at cluster A (via ICT), a fast busy tone is heard.

If i change the remote branch "region" to be the same as CCM-B, then the call gets through, so it has something to do with codecs.

I undo the above "region" changes. When i check the "MTP required" checkbox when configuring the ICT, the call gets through, but it uses up hardware transcoder at the gateway.

Can someone help me to understand why is there a need to check the "MTP required" check box ? If i dun check the "MTP required" check box, can i still get it to work ?

Thanks for your help.


Eng Wee


Re: Codec issue with ICT and IP-IVR


You definitely need a transcoder in this case, because IP-IVR most likely supports only g711 codec and your phones at branch use g729 to talk to rest of the world. When you use MTP checkbox, since your phone is negotiating g729, and IVR supports only g711, the trunk will look in its MRGL for an available MTP. MTP can be software based (g711 only) in Callmanager or MTP can be a trancoder (hardware device, which can do any codec). In this case

a. either you have no MRGL configured on the Trunk or device pool level and your hardware transcoders are not in a MRG, because of which Callmanager selects the first available hardware MTP resource

b. Or you have a MRGL configured under the trunk (or device pool level) which has a hardware transcoder in the list (group).

So you definitely need a transcoder to make this call to work or use g711 for just the calls between the phone and IPIVR.



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Community Member

Re: Codec issue with ICT and IP-IVR

Hi Sankar,

Thanks for your reply. I understand that i need transcoder as IVR supports G.711 and the remote branch phone is using G.729.

I have MRGL configured on both ends of the ICT trunk with hardware transcoder resource.

If i don't use the MTP checkbox at the both end of the ICT trunk, it will not work even i have MRGL configured with hardware transcoder resource.

The setup will only work if i use MTP checkbox at both ends of the ICT. So is it true that MTP checkbox has to be used for such setup ?


Eng Wee

Re: Codec issue with ICT and IP-IVR

MTP is required for functions such as supplementary services. So its safe to have that option checked.

Community Member

Re: Codec issue with ICT and IP-IVR


We encountered a few more problems in the actual deployment when the MTP box is cheked:

(1) fax across ICT will not work

(2) CCM deducted 80kbps of bandwidth instead of 24kbps of bandwidth when the call is actually a G.729.

All these problems are solved when MTP box is unchecked.

THe problem i encountered in the past few post was what we discovered in the lab, we will need to see if the IVR problems happen during our actual deployment when MTP is unchecked.

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