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216 Nortel IP Softphone 2050

Dual-tone Multifrequency

GIPS implements Dual-tone Multifrequency (DTMF) tones playing and

sends in accordance to RFC 2833. DTMF supports event numbers from

1 to 16.

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.

Nortel Communication Server 1000

IP Phones Fundamentals

NN43001-368 02.07

5 February 2009