Polycom Version 1.4.x 17 - Manual (Page 50)

Administrator Guide - SoundPoint ® IP / SoundStation ® IP Features
42 Copyright © 2004 Polycom, Inc.
3.3.3 Local Conference Mixing
The phone’s audio processing subsystem contains a flexible three-party conferencing
capability
2
. This feature can be used to set up local three-party conferences where no
external protocol signaling is involved.
3.3.4 Voice Activity Detection (VAD)
The purpose of VAD is to conserve network bandwidth by detecting periods of rela-
tive “silence” in the transmit data path and replacing that silence efficiently with spe-
cial packets that indicate silence is occurring. For those compression algorithms
without an inherent VAD function, such as G.711, the phone is compatible with the
comprehensive codec-independent comfort noise transmission algorithm specified in
RFC 3389. This algorithm is derived from G.711 Appendix II, which defines a com-
fort noise (CN) payload format (or bit-stream) for G.711 use in packet-based, multi-
media communication systems. The phone generates CN packets (also known as
Silence Insertion Descriptor (SID) frames) and also decodes CN packets, efficiently
regenerating a facsimile of the background noise at the remote end.
Central
(boot
server)
Configuration file:
ipmid.cfg Set the jitter buffer tuning parameters including minimum
and maximum size and shrink aggression.
• For more information, see 4.6.1.6.1.2 Codec Profiles
on page 79.
Local
Web Server
(if enabled) Set the jitter buffer tuning parameters including minimum
and maximum size and shrink aggression.
Navigate to: http:///coreConf.htm#au
Changes are saved to local flash and backed up to <Ethernet
address>-phone.cfg on the boot server. Changes will per-
manently override global settings unless deleted via the
Reset User Settings menu selection.
Local Phone User
Interface None.
2. On SoundStation IP ® 4000, conferences are not available if the G.729 codec is enabled on the phone.
This restriction will be removed in future releases.
Central
(boot
server)
Configuration file:
ipmid.cfg Enable or disable VAD and set the detection threshold.
• For more information, see 4.6.1.6.10 Voice Activity
Detection on page 86.