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MTP Selection - on SIP Trunk - Need Clarification

Hi.

Please follow the following scenario. I have a SIP Trunk on CUCM. That SIP trunk has an MRGL with HW MTPs (SW IOS BASED MTPs) in a MRG-A and SW MTPs (SW on IPVMS) on MRG-B. Let say for example that I have Type A Phones 7940/7960/etc. If I checked MTP Required on the SIP Trunk then CUCM chooses the MTPs based on the MRGL of the trunk and selects the HW MTPs (IOS based). But if instead of checking the MTP Required on the SIP Trunk I decided to enable "Early Offer support for voice and video calls (insert MTP if needed)" on the SIP Profile for the SIP Trunk (as it seems that is the best option now for not using MTP all the time) then when checking the calls setup CUCM always insert an MTP from the IPVMS instead of using the same MRGL logic and using the HW MTP.

My question is if using "Early Offer support for voice and video calls (insert MTP if needed)" on the SIP Trunk. Where does CUCM decides to pick the MTP from? Using the originating device MRGL? or using the SIP Trunk MRGL?

Thanks in advanced and sorry if that was already answered here.

-Jose


4 REPLIES

MTP Selection - on SIP Trunk - Need Clarification

When Early Offer support for voice and video calls (insert MTP if needed) is configured on a trunk's SIP Profile, calls from older SCCP-based phones (see  Endpoint Features Summary ),  SIP Delayed Offer trunks, and H.323 Slow Start trunks will cause  Unified CM to allocate an MTP if an MTP or transcoder has not already  been allocated for that call for another reason. The MTP is used to  generate an offer SDP with a valid media port and IP address. The MTP  will be allocated from the media resources associated with the calling  device rather than from the outbound SIP trunk's media resources. (This  prevents the media path from being anchored to the outbound SIP trunk's  MTP). If the MTP cannot be allocated from the calling device's media  resource group list (MRGL), then the MTP allocation is attempted from  the SIP trunk's MRGL.

HTH

Regards,

Yosh

HTH Regards, Yosh
Community Member

MTP Selection - on SIP Trunk - Need Clarification

Thanks Yosh. On my scenario both the SIP Trunk and the calling device are using the same MRGL which has HW MTPs first and then IPVMS MTPs. So why the MTP selection is different?

-Jose

MTP Selection - on SIP Trunk - Need Clarification

Did you recently assign the devices to the MRGL? If so, have you reset the phones.

You do have the HW_MTP, on the top of the MRGL, right?

HTH

Regards,

Yosh

HTH Regards, Yosh
VIP Super Bronze

MTP Selection - on SIP Trunk - Need Clarification

There are two possible reasons for this..

1. You dont have codec pass-through on your MTP config..

2. Wrong codec capabilities between MTP and the devices that need it..

For each of this issues, please refer to the following threads

1. https://supportforums.cisco.com/message/3855498#3855498

2. https://supportforums.cisco.com/message/4155740#4155740

One of this will resolve your issue

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