UC500 with SIP Trunking, CODECs and transcoding question with CUE

Unanswered Question
Apr 22nd, 2009

Hi all,

I'm looking to deploy UC500 in a customer site and SIP Trunk to a SIP Service Provider. I wish to use G729 for all calls over the SIP trunk where possible.

It's my understanding that CUE only supports G711. Therefore is it possible to transcode locally on UC500, in which case how many transcoding sessions are available on the UC500 products? I won't be using any of the analogue ports so no DSP's will be used for normal calls.

Alternatively is it possible to re-negotiate CODECs so that when a call comes in on the SIP trunk and is sent to the Auto Attendant on CUE it uses G711, but in the case where this same call is then sent/transferred on to an IP Phone it then uses G729. And also for the opposite where a call comes in on a SIP trunk and is answered by a phone using G729 and then transferred to CUE/VM and changes to G711.

Any advice would be appreciated.



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Nicholas Matthews Wed, 04/22/2009 - 05:00

Hi Chris,

With the way the CME handles SIP calls there isn't a way to renegotiate the codec.

By default we'll send a moved temporarily 302, but most providers won't support that and you'll have to turn that off.

But yes, you'll need to transcode.


ccpagel Wed, 04/22/2009 - 05:16

Thanks for the info Nick.

My SIP provider does not support moved temporarily 302 as you suspected.

Do you know if its possible to do transcoding on UC500 (I know this is possible with an ISR and CME) and if so how much transcoding resource / how many sessions can be supported?


Nicholas Matthews Wed, 04/22/2009 - 06:06

Hi Chris,

This depends on the model UC520 you have. I know certain models that have the lower seat count don't have the DSP resources necessary for conferencing.

Check what you want to work against the DSP calculator, and you can figure this out pretty quickly.



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