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conference via PBX interco

Hi everybody,

I need some help or ideas.

This is my issue and I don't know how to solve it


Topology :

IP phones <--> CCM 3.3.3 <--> IOS gateway 12.3.1a <--PRI_E1--> PBX <--> traditional phones <--> PSTN


Test 1 : failed

I want to have an ad-hoc conference using the softkley conference button on the IP phone A

When Ip phone A calls traditional phone B and IP phone A calls traditonal phone C, as soon as the ip phone tries to activate the ad-hoc conference trad phone B and C hang up


Test 2 : success

When I do the same test via the PBX to the PSTN

Ip phone A calls PSTN phone D and PSTN phone E and want to activate the ad-hoc conference it works


Test 3 : success

When I do the same test between 3 local ip phones it ad-hoc conference works too

Have you any idea concerning the failed test 1

Waiting for your help as soon as possible


Cisco Employee

Re: conference via PBX interco

Sounds like there may be a codec issue. The conference bridge is expecting G.711. If the PBX calls use G.729 then you will need a transcoder.

Please verify your codec and transcoding configuration. You may need to look at Detailed CCM traces to verify the codecs are negotiated probperly and that the transcoder is invoked properly.

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