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Silence suppression/VAD
Issue 6 January 2008 253
● 320 channels of V.32 SPRT
The above channel counts are the same if AES encryption and SHA-1 authentication are
enabled.
The One-X Deskphones (96xx) support the G.722 codec with 64 kbps and with 20 ms packets
Generally, G.711 is used on LANs because bandwidth is abundant and inexpensive whereas
G.729 is used across bandwidth-limited WAN links.
G.726 Codec and H.248 Media Gateways
As of Communication Manager release 3.1, media processing resources on H.248 Media
Gateways support the G.726 codec. The following table provides the corresponding capacities:
Silence suppression/VAD
Voice Activity Detection (VAD) or silence suppression can also be used to save bandwidth.
During a conversation, because only one party is speaking at any given time, more than 40% of
the transmission is silence. Voice Activity Detection (VAD) in Avaya IP telephones monitor the
locally produced voice signal for voice activity. When no activity is detected for the configured
period of time, packets are no longer transmitted. This prevents the encoder output from being
transported across the network when there is silence, resulting in bandwidth savings.
When silence suppression is enabled, the remote end is instructed to generate "comfort noise"
when no voice is present to make the call sound more natural to users. The trade-off with
silence suppression lies with the silence detection algorithm. If it is too aggressive, the
beginnings and ends of words can be "clipped." If not aggressive enough, no bandwidth is
saved.
Silence suppression is built into G.729B. It can be enabled for other codecs from within
Communication Manager. Because of voice quality concerns with respect to clipping, silence
suppression is generally disabled (with the exception of G.729B).
The following Avaya products employ silence suppression to preserve bandwidth:
● Avaya Communication Manager software (for control)
Table 47: Number of Simultaneous Bi-Directional Connections Supported
Codec G250 G350 G700
G.726A Unencrypted 10 16 32
G.726A with AEA Encryption 10 16 32
G.726A with AES Encryption 10 12 24