[cisco-voip] Ulaw -Alaw and MTP resources

[Ryan Ratliff]

If you were actually transcoding one of those legs would be doing alaw and the other ulaw.  What you see is two ulaw legs which means that your MTP is acting just like an MTP.  I assume by enabling the SIP trunk for MTP you mean you've checked the "MTP Required" box?  That box does just what it says it does, it forces an MTP for each call.  

You aren't wasting MTP resources for transcoding between alaw and ulaw, you are wasting them because you checked the box.

I'd guess that you are actually using a uniform codec (look at the rtp streams on your mgcp gateway when a call is active and I'm sure you'll see they are ulaw there too) just not the codec you want.

You've got two options for forcing ulaw vs alaw.  The first is a custom codec preference list with 711ulaw at the bottom of the list (you can't disable codecs this way, just prioritize them).  Look at System->Region Information->Audio Codec Preference List.  The second option is to disable g.711 ulaw via the service parameter "G.711 mu-law Codec Enabled". 

You may need to upgrade to get one or both of those options.

-Ryan

On Nov 19, 2012, at 8:40 AM, abbas Wali <abbaseo at gmail.com> wrote:

Hi all, 

just to clairfy, we have confirgured PCM Type to ALaw (as in UK) on the MGCP gateways but all calls received shows ULaw on the phones. 

I believe our MGCP gateway is transcoding them as below

Gateway3#show voice dsp active  
 
DSP  DSP                DSPWARE CURR  BOOT                         PAK     TX/RX
TYPE NUM CH CODEC       VERSION STATE STATE   RST AI VOICEPORT TS ABORT  PACK COUNT
==== === == ======== ========== ===== ======= === == ========= == ===== ============

 
----------------------------FLEX VOICE CARD 0 -----------------------
-------
                        *DSP ACTIVE VOICE CHANNELS*
DSP    DSPWARE              VOX DSP                 SIG DSP          PAK   TX/RX
TYPE   VERSION    CODEC     NUM CH TS VOICEPORT SLT NUM CH TS RST AI ABRT PACK COUNT
====== ========== ========  === == == ========= === === == == === == ==== ============
C5510      27.3.1 g711ulaw  001 01 29 0/0/0:15  000 002 12 29   0  0    0  13359/13680
C5510      27.3.1 g711ulaw  001 02 31 0/0/0:15  000 002 14 31   0  0    0    3707/3816

The SIP trunks are enalbed to use MTP resources  and the MTP Preferred Originating Codec is set to ALaw. 

I think we are wasting alot of MTP resources converting from A to U. is there a way to use a uniform codec in CUCM 8.5. 

Many thanks 
-- 
@bbas.. 

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