MTP and Voice Class Codec

[yourid]

I am hoping to have someone clear up a little confusion that I have about MTP and Voice Class Codec.  I have the following lab configured below and would like to actually, be able to see functionality break when I'm not using an MTP or have voice class codec configured.  If I have to, I would change my configuration around and add a gatekeeper into the mix.

When exactly should a software MTP?  Since a transcoder is an MTP and is already doing the conversion from g711 to g729.  when and why would you need an MTP? According to the SRND, it states that I would need an MTP when using supplementary services.  But so far, when i place a call on hold without and MTP, everything seems to work correctly.

Why would I need to configure IOS gateway Voice Class Codec?

voice class codec 1

     codec preference 1 g711ulaw

     codec preference 2 g711alaw

     code preference 3 g729r8

I have the following configuration:

CUCM 7.x, Unity Connection ,UCCX,Presence

Site 1 - MGCP gateway connected to CUCM

          MOH Mulitcast

          Call-Agent for UCCX

          Site 1 users should be able to leave messages for users at Site 3

Site 2 - H323 gateways connected to CUCM

          SRST fallback

               4 digit dial back to site 1

               voicemail access via the message button in SRST mode

          MOH Mulitcast

          Call-Agent for UCCX

          Site 2 users should be able to leave messages for users at Site 3

Site 3 - MGCP gateway connected to CUCM

          CUE connected to CUCM

          CME SRST fallback

               4 digit dial back to site 1

               voicemail access via the message button in SRST mode

          MOH Mulitcast

[Marwan ALshawi]

Hi

About the MTP according tom the SRND it used for supplementary services for example mismatch int the h323 or SIP versions or messages in the case you will need software or hardware MTP

Also the software MTP provide you with transcending of the same codec but different packetization such as g711ulaw to g711alaw

While enhanced hardware MTP could be used like transcoder

In other words the MTP is nor always needed

About the voice class

It is a codec election preference and let the dial peer negotiate the codec with incoming call so that the dial peer can support multiple  codecs and negotiated using the preference configured in it 

You can enforce the codec using the command codec under the dial peer config but in this case if the calls come from pstn and go to uccx and uccx codec is g729 and the dial peer codec set to g711 manually then without transcoder configured and assigned to the uccx CTI ports the call will fail due to codec mismatch while using the class codec the dial peer can negotiate the codec

Hope this help

If helpful rate