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
<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://<phoneIPAddress>/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 <VAD/> on page 86.