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New Member

One way voice problem

Hi all,

I´m getting one way voice between a CCM4.02Sr2c and a Panasonic IP enabled PBX. I´v configured the Panasonic PBX as an h323 gateway in Callmanager. Result: The PBX users can hear me - I can´t hear them. Doesn´t matter who set up the call. I have tried some different codings, MTP enabled and also disabled. No difference. I also worked in Service parameters to not force a symmetric payload size. No difference.

On my Cisco Phones I can see the RX-Counter running up with G711u, but I can´t hear some voice. When I use ethereal there´s "nothing" in the stream. (maybe noise)

When I do the test to the Panasonic PBX directly with an H323 Softphone, everything works fine! I see the PBX´s RTP packets coming in with an SSRC-ID fivethousandsomething. My own ID is much much higher (so I used to know the SSRC) Does this low ID cause problems to the MTP or the phones?

I do not have a hardware MTP in place with which I could test transcoding.

Any ideas (beside kicking the Panasonic PBX :-)))) ?

Thanks in advance you for your help.

Best Regards from pretty cold Germany,



Re: One way voice problem

I think IP enabled PBX is similar to H.323 gateway , Try the below document.

New Member

Re: One way voice problem

Hi, I already knew this document. Anyway, this is a connection between CCM and a Panasonic H323 IP PBX and there is no chance of configuring "voice rtp send-rcv" on the Panasonic nor on CCM ;-)

The fact is, between a "normal" H323 client (OpenPhone) and the Panasonic everything works fine.

But thank you for your idea.

Best Regards,


Re: One way voice problem

Hello Markus,

In case your observation with ethereal is true (), then the problem should be not the Cisco Phone per se.

Can you trace the H323 setup through CCM and by the Softphone? Are there differences?

I would guess the call setup differs somewhere so the IP PBX does not deliver useful content in the voip packets.

Hope this helps! Please rate all posts