Solved: Codecs for Gateways & Phones

raja Saravanan · ‎11-01-2012

Dear Friends,

How Gateways decide on what codec to use, does it depend on Region configuration, further Phones supports certain codecs by default, what codecs does gateways support, what is the DSP resource used for this function by gateway ( not transcoding ).

Does phones have DSP builtin to generate configured codecs ( decided during media negotiation ), how the sampling technique is determined by the phone for the codec selected during media negotiation.

Cheers,

Shaggy

mkchandak · ‎11-01-2012

How Codec is selected depends on what kind of a Gateway you have.

For MGCP, it uses Region settings, which is in the same order in which IP Phones select the codec. Do remember that when you are using SCCP, Phone is a dumb device. All signalling is done by CUCM. So, it uses the codec order provided by CUCM.

For SIP and H323, it depends on voice class codec defined on the gateway and uses the order configured on the list.

Phones do have a DSP which does all the encoding/decoding, but it depends on CUCM to decide which codec to be used.

View solution in original post

Jonathan Schulenberg · ‎11-02-2012

Ultimately CUCM determines the codec choosen. The Codec Preference Order (static until 9.0) will choose the best-sounding audio codec supported by both endpoints and allowed by the region settings.

All endpoints/gateways tell CUCM what they support. For SCCP phones they do this at registration, MGCP does it in CRCX, SIP in INVITE, H323 in H245, etc. IOS uses G.729 for H323/SIP dial-peers by default unless you add a voice class codec.

Please remember to rate helpful responses and identify helpful or correct answers.

View solution in original post

mkchandak · ‎11-01-2012

How Codec is selected depends on what kind of a Gateway you have.

For MGCP, it uses Region settings, which is in the same order in which IP Phones select the codec. Do remember that when you are using SCCP, Phone is a dumb device. All signalling is done by CUCM. So, it uses the codec order provided by CUCM.

For SIP and H323, it depends on voice class codec defined on the gateway and uses the order configured on the list.

Phones do have a DSP which does all the encoding/decoding, but it depends on CUCM to decide which codec to be used.

Jonathan Schulenberg · ‎11-02-2012

Ultimately CUCM determines the codec choosen. The Codec Preference Order (static until 9.0) will choose the best-sounding audio codec supported by both endpoints and allowed by the region settings.

All endpoints/gateways tell CUCM what they support. For SCCP phones they do this at registration, MGCP does it in CRCX, SIP in INVITE, H323 in H245, etc. IOS uses G.729 for H323/SIP dial-peers by default unless you add a voice class codec.

Please remember to rate helpful responses and identify helpful or correct answers.

raja Saravanan · ‎11-04-2012

Dear Friends,

Thank you very much !!!

cheers,

Shaggy

raja Saravanan · ‎11-17-2012

Dear Friends,

I have one more doubt, which DSP resource will be used by gateway to generate voice streams based on the agreed codec during media negotiation, the voice termination DSP's ?

cheers,

Shaggy