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Microsoft Lync Edition Administrator’s Guide for SIP-T2_Series and T4_Series IP Phones
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2. Select the desired value from the pull-down list of VAD.
3. Click Confirm to accept the change.
Comfort Noise Generation (CNG) is used to generate background noise for voice
communications during periods of silence in a conversation. It is a part of the silence
suppression or VAD handling for VoIP technology. CNG, in conjunction with VAD
algorithms, quickly responds when periods of silence occur and inserts artificial noise
until voice activity resumes. The insertion of artificial noise gives the illusion of a constant
transmission stream, so that background sound is consistent throughout the call and the
listener does not think the line has released. The purpose of VAD and CNG is to maintain
an acceptable perceived QoS while simultaneously keeping transmission costs and
bandwidth usage as low as possible.
Note
For example, A is talking with B.
A: VAD=1, CNG=1
B: VAD=0, CNG=1
If A mutes the call, since VAD=1, A will send CN packets to B. When receiving CN
packets, B will generate comfortable noise.
If B mutes the call, since VAD=0, B will not send CN packets to A. So even if CNG=1 (B),
A will not hear comfortable noise.
VAD is used to send CN packets when phone detect a "silence" period; CNG is used to
generate comfortable noise when phone receives CN packets from the other side.