Silence suppression/VAD
Issue 3.4.1 June 2005
213
Silence suppression/VAD
Besides low bit rate, 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 the IP telephone
monitors the locally produced voice signal for voice activity. When no activity is detected for the
configured period of time, the Avaya software informs the Packet Voice Protocol. 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 not used (with the exception of G.729B).
The following Avaya products employ silence suppression to preserve bandwidth:
●
Avaya Communication Manager software (for control)
●
Avaya 4600 series IP Telephone
●
Avaya IP SoftPhone
●
Avaya Media Gateways
For procedures to administer QoS parameters, refer to Administration for Network Connectivity
(555-233-504).
Transcoding/tandeming
Transcoding or tandeming describes a voice signal that has been passed through multiple
codecs, such as can be the case when call coverage is applied on a branch office system back
to a centralized voice mail system, the calls may experience multiple transcodings (this could
include G.729 across the WAN and G.723.1 into the voice mailbox). Each transcoding action
results in degradation of voice quality. These problems may be minimized by the use of the
Communication Manager feature called DCS with Rerouting (Path Replacement). This feature
detects that the call coming through the main ECS has been routed from one tandem ECS,
through the main, and back out to a third switch. In these cases, the system then re-routes the
call directly, thus replacing the path through the main system with a more direct connection.
Avaya products minimize transcoding while non-Avaya products may cause slight to excessive
transcoding. "Shuffling" and "Hairpinning" also reduce transcoding.
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...