H323 Trunk - G729 fast start issue

Unanswered Question
Apr 21st, 2008


We are trying to interconnect a CUCM 6.1 with an IP-to-IP GW in order to translate H323 messages to SIP (Sip Provider).

The problem is that we are not able to place calls with G729(MTP) but only G711.

We need Fast Start with G729 MTP because our Sip Provider supports "Early Offer"

Is there any specific config that has to be done on IP-to-IP GW in order to enable

fast start ?



I have this problem too.
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chrlayios Mon, 04/21/2008 - 06:28

Thanks Matt,

I have already done that but I am stil not able to place calls with G729 MTP


matthewpage Mon, 04/21/2008 - 06:33

Can you upload your config? Have you read the documentation i added?


chrlayios Mon, 04/21/2008 - 06:53

Please find below my config:

voice service voip


allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

allow-connections sip to sip



h225 h245-address on-connect

h245 passthru tcsnonstd-passthru


rel1xx disable

voice class codec 30

codec preference 1 g729r8

codec preference 2 g729br8

codec preference 3 g711alaw

codec preference 4 g711ulaw

voice class h323 1111

h225 connect-passthru

call start fast

h245 passthru all

telephony-service ccm-compatible


dial-peer voice XXX voip

voice-class codec 30

voice-class h323 1111

incoming called-number .

no vad

dial-peer voice XXX voip

preference 2

destination-pattern .T

redirect ip2ip

voice-class codec 30

session protocol sipv2

session target ipv4:X.X.X.X

no vad



matthewpage Mon, 04/21/2008 - 07:12

Hi Chris

It seems a lot of people have had similar problems. Take a look at this one:


Looking at the other guide it says that the codec and payload need to be assigned statically. Could give this a try:

dial-peer voice 40 voip

codec G729r8 bytes 30

Also do you have any transcoding setup? As this will be required to go from g711 to g729.



chrlayios Mon, 04/21/2008 - 10:35

Hello Matt,

Thanks for your reply.

According to some documents that I have already read, there is no need for transcoding. Besides it is mandatory for us to

have G729 for the entire voice path.

Another fact that makes me believe that the above scenario is true, is that on CUCM's H323

Trunk Configuration page I have ortion for G729 fast start.

I hope i am not far away from the truth !!


matthewpage Mon, 04/21/2008 - 11:18

If the call starts with G729 then i guess you wouldnt need a trascoder but you would need the MTP for the h323 to sip part.

Maybe have a look at the call manager SDI logs it may shed some light as to what is happening. To me it seems like a resources issue if g711 works but g729 doesnt. I could be very wrong though.


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