Low-delay audio packet transmission, Jitter buffer and packet error concealment, Voice activity detection – Polycom SOUNDPOINT SIP 3.1 User Manual
Page 128: Emplo
Administrator’s Guide SoundPoint IP / SoundStation IP
4 - 74
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Low-Delay Audio Packet Transmission
The phone is designed to minimize latency for audio packet transmission.
There are no related configuration changes.
Jitter Buffer and Packet Error Concealment
The phone employs a high-performance jitter buffer and packet error
concealment system designed to mitigate packet inter-arrival jitter and
out-of-order or lost (lost or excessively delayed by the network) packets. The
jitter buffer is adaptive and configurable for different network environments.
When packets are lost, a concealment algorithm minimizes the resulting
negative audio consequences.
Configuration changes can performed centrally at the boot server or locally:
Voice Activity Detection
The purpose of voice activity detection (VAD) is to conserve network
bandwidth by detecting periods of relative “silence” in the transmit data path
and replacing that silence efficiently with special 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
comfort noise (CN) payload format (or bit-stream) for G.711 use in
packet-based, multimedia communication systems. The phone generates CN
Central
(boot server)
Configuration file:
sip.cfg
Set the jitter buffer tuning parameters including minimum and
maximum size and shrink aggression.
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For more information, refer to
Codec Profiles <audioProfile/>
on
page
.
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 permanently
override global settings unless deleted through the Reset Local
Config menu selection and the <Ethernet address>-phone.cfg is
removed from the boot server.