Echo Cancellation; Clock Synchronization; Jitter Buffer; Qos - Nortel 1110 Fundamentals

Telchemy VQMon
GIPS includes Telchemy VQMon library. The Telchemy VQMon library
collects and provides Voice Quality statistics information.

Echo cancellation

Echo can generate electrically when an impedance mismatch occurs, or
can generate acoustically by feedback from a speaker or ear piece to a
microphone. Any echo that returns to the IP Softphone 2050 is more
noticeable to the listener because of the additional delay the IP connection
introduces.
The Voice Gateway Media Card includes echo cancelers as part of its
function cancels echo which the TDM side of the Media Gateway generates.
Echo cancellers enable when audio passes through the Voice Gateway
Media Card.
Because the IP Softphone 2050 does not provide an echo canceller, a
slight echo from acoustic coupling on the headset can occur in some call
situations.

Clock synchronization

Buffer underruns and overruns can occur since no sample clock is at the
receiving end of an IP audio stream synchronized to the transmitting clock.
The buffer overruns and underruns are corrected by two mechanisms,
both of which apply to the IP Phones and the DSPs on the Voice Gateway
Media Card.

Jitter buffer

Use the default value sent from the TPS (the value configured in TM–
[Nortel recommends that you use the default value]) to configure the IP
Softphone 2050 jitter buffer.
The jitter buffer has a desired size and a maximum allowable size. If the jitter
buffer exceeds its maximum allowable size, sufficient frames are discarded
to reduce the contents of the jitter buffer to the desired setting. If the jitter
buffer underruns, frames are held in the jitter buffer until it fills to the desired
level. Both underrun and overrun result in a discontinuity in the audio.
For codecs that support silence suppression, the jitter buffer is
resynchronized at the beginning of each talk spurt.

QoS

A combination of codec selection, jitter buffer and packet time, and the
use of the DiffServ Code Point (DSCP) of the network contributes to the
end-to-end Quality of Service (QoS).
Copyright © 2003–2007, Nortel Networks
.
Nortel Communication Server 1000
IP Phones Fundamentals
NN43001-368 02.01 Standard
Release 5.0 7 December 2007
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