These features are configured in the IMG 1010 - IP Bearer Profile pane

 Silence Silence Suppression:

During a normal voice conversation, much of the time is wasted on silence from one or both ends. Ethernet bandwidth can be conserved if during these periods of silence RTP packets are sent with silence-encoded compressed payloads. The IMG Silence Suppression feature supports the concepts of Voice Activity Detection (VAD) and Comfort Noise Generation (CNG). When enabled Silence suppression will not send RTP traffic during periods of silence, saving bandwidth usage. At the beginning of a silence period, a single packet will be sent to the distant end to inform it that a period of silence is being entered, and that the distant end should begin to regenerate comfort noise to its TDM stream. Silence Suppression can be enabled or disabled on an established connection.

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