Unanswered Question
Apr 27th, 2009


i have set up MTP resources on IOS router to be used with Call Manager for alaw to ulaw conversion.

I configured three MTPs on the gateway, one for alaw, one for ulaw and one for clear and added all three of them to media resource list on Call Manager:

dspfarm profile 1

codec g711alaw

maximum sessions software 100


dspfarm profile 2

codec g711ulaw

maximum sessions software 100


dspfarm profile 3

codec pass-through

maximum sessions software 100


The SIP trunk between Call Manager and the gateway has MTP required checked and g711alaw codec as preffered codec, since most calls work with alaw towards the provider.

However, i want some calls to be ulaw, so i have set ulaw on specific dial-peers toward Call Manager.

The problem is that the MTP doesnt convert between alaw and ulaw as it should, so the only way i can make this work is if i use transcoding directly on the gateway.

Could the problem be with 3 different MTPs or with g711alaw preffered setting on the trunk?

Debug ccsip messages gives me "SIP 501 not implemented error" , q.850 65 cause code. If i use transcoding on gateway itself, it works, otherwise nothing is sent to Call Manager.

This is what i get, when i use transcoding (this is on call, but has 2 xcode and 2 mtp sessions):

19 19 xcode sendrecv g711u 18704 2000

19 20 xcode sendrecv g711a 18028 2000

16969882 16875147 mtp sendrecv g711u 17612 31540

16969882 16875146 mtp sendrecv g711u 19136 19424

( is the gateway, is endpoint)

Best regards,


I have this problem too.
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chadlincoln Mon, 04/27/2009 - 03:54

If you are going from one codec to another, you are correct in thinking you'd need a transcoder instead of a MTP.

markotisler Mon, 04/27/2009 - 03:55

But shouldnt MTP take care of alaw to ulaw conversion also? As i recall this souldnt need a transcoder...


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