turning off VAD when using IP Phone speakerphone

[abulatkin]

It looks like when we use speakerphones for a call between 2 IP Phones (7940) there's silence suppression (without comfort noise). Is there any way to turn it off (or enable some comfort noise)?

[ebreniz]

VAD also provides Comfort Noise Generation (CNG). Because you can mistake silence for a disconnected call, CNG provides locally generated white noise so the call appears normally connected to both parties. G.729 Annex-B and G.723.1 Annex-A include an integrated VAD function, but otherwise performs the same as G.729 and G.723.1, respectively.

In Cisco CallManager, VAD can be enable (it is disabled by default) with the following service parameter:

SilenceSuppressionSystemWideThis parameter selects the VAD setting for all skinny endpoints (for example: Cisco IP Phones and Skinny gateways)

SilenceSuppressionWithGatewaysThis parameter selects the VAD setting for all MGCP gateways. This does not have an effect on H.323 gateways. VAD on H.323 gateways must be disabled on the gateway.

You can find these service parameters under Cisco CallManager Administration (Service > Service Parameters > select_server > Cisco CallManager).

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml

[abulatkin]

In my case the G.711 codec is used and the SilenceSuppression service parameter defaults to NO. So when using the handset everything is ok, but when both users talk over speakerphones there seems to be silence suppresion (or maybe noise suppression).