SIP G729

[jon83]

Hi how do you force SIP trunks on a 3300 to use only G729?
I've placed the SIP peer in a different zone but calls still use G711.???

DO I need more DSP resources? I have an MXE with a dual DSP?

 

[Mitelpassion]

you shouldn't need DSP resources for SIP comression.

odd that your not getting compression.

 

[slapin]

Do all the parties support G.729?

 

[IrwinMFletcher]

Note that a lot of SIP trunk calls at one point or another land on the pbx, so G729 is important on the system.

Also, check to make sure that the SIP trunk is Offering G729. Wireshark is handy for this.

 

[Mitelpassion]

if both parties support G729, would a dsp still be required.
my theory is no..

 

[IrwinMFletcher]

It would if you want any features to be G729 as well. For example, if the called party puts the call on hold, the stream will be changed to come from the pbx to the sip trunk. If you want that stream to be compressed, then the pbx needs a compression license.

My point though was that just because the endpoints support a particular codec, it doesn't mean it is sent in the Offer. That information, for SIP devices is configurable, while it's hard coded for the 3300 to use G729 if available (and the zoning matches, etc). I would use wirehark to decode the SIP session and verify that the SIP trunk is actually offering/answering with G729 as the first step.