Nortel VoIP Gateway, Configuration Manual

Page: 172 / 220

172 Comfort noise
P0606298 02
When several calls are made over a full duplex link, all calls share the same transmit path and they
share the same receive path. Since the calls are independent, the peak bandwidth must account for
the possibility that all speakers at one end of the link may talk at the same time. Therefore, the
peak bandwidth for n calls is n * the full transmission rate. The following figure shows the peak
bandwidth requirements for two calls on a full duplex link with silence compression. Note that the
peak bandwidth is twice the full transmission rate, even though the average bandwidth is
considerably less.
The spare bandwidth made available by silence compression is available for lower priority data
applications that can tolerate increased delay and jitter.
Figure 53 Two calls on a full duplex link with silence compression
Comfort noise
To provide a more natural sound during periods of silence, comfort noise is added at the
destination gateway when silence compression is active. The source gateway sends information
packets to the destination gateway informing it that silence compression is active and describing
what background comfort noise to insert. The source gateway only sends the information packets
when it detects a significant change in background noise.
Time ->
B
an
d
w
idth -
>
Bandwidth Used
Time ->
B
an
d
w
id
th
-
>
Tx
C
h
an
Rx C
h
an
Independent Tx and Rx bandwidth
not shared by “half-duplex” calls. Peek channel bandwidth is
n * peek bandwidth per call.
Conversations
Rx
Tx
Fred Here.
Hello Fred. This is Susan. Do you have a minute?
Sure! Hi!
Rx
Tx
Fred Here.
Hello Fred. This is Susan. Do you have a minute?
Sure! Hi!
Rx
Tx
Hola Isabella!
Buenos noches Juan. Muy bien, y tu?
Como estas?
Rx
Tx
Hola Isabella!
Buenos noches Juan. Muy bien, y tu?
Como estas?
Channel Max
Channel Max
Hello Fred. This is Susan. Do you have a minute?
Conversation
Fred here.
Hi! Sure!
Conversation
Bandwidth used
Peak channel bandwidth is n * peak
bandwidth per call
Time
Channel/Link max
Tx
Rx
Tx
Rx
Buenos noches Juan
Muy bien, y tu?
Hola Isabella Com o estas?
Independent Tx and Rx bandwidth not
shared by half-duplex calls
Time
Channel/Link max
Tx
c
h
a
n
ne
l
B
a
ndw
id
th
Rx
c
h
a
n
n
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l
Ba
nd
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