UCM6.1 - h323 gateway questions

Answered Question
Jul 29th, 2008

From callmanagers perspective Is it possible with a single h323 gateway defined in callmanager to allow outbound calls to our WAN (to external sites that have their own VOIP systems and h323 gateways) to use G.729, while ensuring inbound calls from the PSTN always use G711? I know how to configure the dial-peers on the gateway, but i'm looking for help on callmanager side I.e. if I use the default region in the device pool assigned to the h323 gateway, and default region uses system defaults (g711 internal g729 external) will calls out to the wan (whose dial-peers specify g729) use G729 without a transcoder? And also ensure that calls coming in from the PSTN use G711 (without having to invoke a transcoder for either of these? On the gateway side calls inbound from wan site send 7 digits and from the pstn I get four, so I'm able to do two different dial-peers destined for callmanager with the respective g711 or g729 defined.

With this same above setup, if I check the media termination point checkbox on h323 gateway page in ccm, does this "force" the call to use G711? I read a post that it does but want validation. I need the MTP as we need consultive transfer with wan sites.


I have this problem too.
0 votes
Correct Answer by Ayodeji oladipo... about 8 years 2 months ago

CCM will send the call to the gw as g711.. the gateway will then try and send the 2nd call leg as g729...

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Overall Rating: 4.5 (3 ratings)
Ayodeji oladipo... Tue, 07/29/2008 - 03:44


1. The codec you call will use will be determined the codec you select for the dial-peer responsible for routing the calls.

If the dial-peer configured to orute the callt o the WAN VoIP uses the default G.729, then the calls wil use G.729.

If the incoming dial-peer routing the call from the pstn uses G.711 then the calls will use G.711 to call manager.

with an h.323 gateway you actually do not have any need for a xcoder as H.323 gateways can negotiate codec capabilities..

To do this configure this...

voice class codec 1

codec preference 1 g711ulaw

codec preference 2 g729r8.

Then apply the Voice calss to the apprioriate dial-peer.

This way the gateway can negotiate between g.729 and g.711.

For digit manipiulation..Calls from the WAN uses 7 digits, call from PSTN uses 4 digit extension. I believe that your internal users use 4 digit extensions. ALl you have to do is set your signifance digits under incoming calls of the gateway in callmanager to 4.

MTP, does not force a call to use a codec type. Codec selection are determined by the regions your ip phones are in or the dial-peer used on your voice gateway.

MTP is used for supplementary services like consultive transfer.

HTH, pls rate useful posts

UCcomp2007 Tue, 07/29/2008 - 04:05

HI aokanlawon.

Another question. which is a little different than first setup/question

I was on a call with TAC last night, and what they said was that if I have a g711 region defined for the h323 gateway (in device pool) that all calls would use G711 regardless of what codec statement is on gateway dial-peer. Is that accurate?

Correct Answer
Ayodeji oladipo... Tue, 07/29/2008 - 04:27

CCM will send the call to the gw as g711.. the gateway will then try and send the 2nd call leg as g729...

Marwan ALshawi Tue, 07/29/2008 - 06:22

so, regarding to this

if i have h323 gateway with 10 calls from g711 to g729a no need for any dsp resources to make xconding ?

and if i have the same case but with an MGCP gateway i will need the xcoding ?

because as i know xcoding required for any

just confused!


resources can be used to transcode G.729 to G.711

also if u have link regarding this will be great

Ayodeji oladipo... Tue, 07/29/2008 - 06:38


With H.323 gateways, you actually do not need a xcoder. You can just configure your voice class command to enable the gateway to negotiate between different codecs.

With MGCP, yes you need a xcoder.

A xcoder help to convert codecs from 2 different voip stream. It could be G.711 to G.722 or G.729 to G.711.

Marwan ALshawi Tue, 07/29/2008 - 06:42

thanks for respons

sure i know what xcoder and what to do but i am just wondring about h323 and mgcp

so in this case h323 cost-saving cos u dont need extra modules for xcoding

then why mgcp prefered

i know it give kind of centrlization with CCM or CUCM but regarding xcoding issue it is not cost-saving

am i right ?


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