Effects of Articulation Activity Detection on Bandwidth
Statistically, an accumulated of 24 calls or added ability accommodate 35 percent silence. With traditional
telephony articulation networks, all G.711 articulation calls use 64 kbps fixed-bandwidth
links behindhand of how abundant of the chat is accent and how abundant is silence. In
Cisco VoIP networks, all conversations and silences are packetized. VAD can suppress
packets absolute silence. Instead of sending VoIP packets of silence, VoIP gateways
interleave abstracts cartage with VoIP conversations to added finer use arrangement bandwidth.
Table 2-7 illustrates the blazon of bandwidth accumulation VAD offers.
Table 2-7 Impact of VAD on Required Bandwidth
Codec Speed Sample Size Frame Relay Frame Relay
Codec (bps) (Bytes) (bps) with VAD (bps)
G.711 64,000 240 76,267 49,573
G.711 64,000 160 82,400 53,560
G.726r32 32,000 120 44,267 28,773
G.726r32 32,000 80 50,400 32,760
G.726r24 24,000 80 37,800 24,570
G.726r24 24,000 60 42,400 27,560
G.726r16 16,000 80 25,200 16,380
G.726r16 16,000 40 34,400 22,360
G.728 16,000 80 25,200 16,380
G.728 16,000 40 34,400 22,360
G.729 8000 40 17,200 11,180
G.729 8000 20 26,400 17,160
Codec (bps) (Bytes) (bps) with VAD (bps)
G.723r63 6300 48 12,338 8019
G.723r63 6300 24 18,375 11,944
G.723r53 5300 40 11,395 7407
G.723r53 5300 20 17,490 11,369
Chapter 2: Considering VoIP Architecture Elements 91
Note Bandwidth accumulation of 35 percent is an boilerplate amount and does not booty into
account loud accomplishments sounds, differences in languages, and added factors.
Note For the purposes of arrangement architecture and bandwidth engineering, VAD should
not be taken into account, abnormally on links that backpack beneath than 24 articulation calls
simultaneously.
Various features, such as music on authority (MOH) and fax, cede VAD ineffective. When
the arrangement is engineered for the abounding voice-call bandwidth, all accumulation provided by VAD
are accessible to abstracts applications.
VAD is enabled by absence for all VoIP calls. Not alone does VAD abate the blackout in
VoIP conversations, but it additionally provides CNG. In some cases, blackout ability be mistaken
for a broken call. CNG provides locally generated white babble to accomplish the call
appear commonly affiliated to both parties.
For example, a aggregation is assessing the aftereffect of VAD in a Frame Relay VoIP environment.
The aggregation affairs to use G.729 for all articulation calls bridge the WAN. Previously,
it was bent that anniversary articulation alarm aeroembolism with G.729 uses 26,400 bps. VAD can
reduce the bandwidth appliance to about 17,160 bps, which constitutes a bandwidth
savings of 35 percent.