Does anybody which end of a call is resonsible for using an MTP?
Is it the caller?
..... the called part?
..... or always Call Manager?
I am trying to troubleshoot a one way audio issue on inbound calls after call is placed on hold and then resumed.
We have an integration between CCM4.3(2) and a Nortel CS2K Softswitch. The Cisco IP Phones are using G729a 20ms and the Nortel CS2K Softswitch is using G711alaw 10ms. Consequently, we have deployed a Cisco 3825 SP Services 12.4(16b) as a hardware transcoder.
We can establish successfully inbound and outbound calls. However, when the inbound call is modified (placed on hold) we get one way audio.
Traces show that outbound calls utilise hardware MTP but inbound calls do not.
Furthermore, packet traces also show that there are duplex G711 A LAW RTP streams between the xcoder and Nortel softswitch before and during the call is placed on hold. But after a Resume softkey is pressed, the xcoder starts sending G711 U LAW RTP packets to the softswitch. This is successfully relayed to the phone on the softswitch but the RTP stream from the Nortel switch, still G711 A LAW to the xcoder is not relayed to the IP phone.
Obviously, we have a codec mismatch, but can not tell why it changes to ULAW after placing a call on hold. Is this a defect with the IOS or is there something wrong with our configuration?
PSTN <- Nortel H323 Softswitch (G711alaw 10ms) <- c3825-spservicesk9-mz.124-16b (XCODER/HW MTP) <- CCM 4.3(2) <- (G729a 20ms) CP7941
Outbound call from IP Phone to PSTN is successfully established. One transcoder session and one hardware MTP session is used. When call is placed on hold by IP phone and then resumed a two way audio stream is re-established.
PSTN -> Nortel H323 Softswitch (G711alaw 10ms) -> c3825-spservicesk9-mz.124-16b (XCODER) -> CCM 4.3(2) -> (G729a 20ms) CP7941
Inbound call from PSTN to IP Phone is successfully established. One transcoder session is used but no hardware MTP session is used (for some reason). However, when call is placed on hold by IP phone and then resumed there is audio from IP phone to PSTN but not PSTN to IP Phone.
Any help much appreciated.