The term silence suppression is used in telephony to describe the process of not transmitting information over the network when one of the parties involved in a telephone call is not speaking, thereby reducing bandwidth usage.
Given that typically only one party in a conversation speaks at any one time, silence suppression can achieve overall bandwidth savings in the order of 50% over the duration of a telephone call.
When silence suppression is active, the line appears to have gone dead at the other (egress) end of the call.
Speech activity detection does not work well on non-speech calls (fax or modem communication, for example).
Thus, silence suppression is generally an optional feature on telephony devices.