Nortel VoIP Gateway, Configuration Manual

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168 Silence Compression on Half Duplex Links
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Silence Compression on Half Duplex Links
The following figure shows the bandwidth requirement for one call on a half-duplex link without
silence compression. Since the sender and receiver share the same channel, the peak bandwidth is
double the full transmission rate. Because voice packets are transmitted even when a speaker is
silent, the average bandwidth used is equal to the full transmission rate.
Figure 48 One call on a half duplex link without silence compression
When silence compression is enabled, voice packets are only sent when a speaker is talking. In a
typical voice conversation, while one speaker is talking, the other speaker is listening – a half
duplex conversation. The following figure shows the peak bandwidth requirements for one call on
a half-duplex link with silence compression enabled. Because the sender and receiver alternate the
use of the shared channel, the peak bandwidth requirement is equal to the full transmission rate.
Only one media path is present on the channel at one time.
Figure 49 One call on a half duplex link with silence compression
Tx+Rx Cha
n
Time ->
B
andwidt
h
-
>
Conversation
Bandwidth Used
Rx
Tx
Fred Here.
Hello Fred. This is Susan. Do you have a minute?
Sure! Hi!
Voice frames sent even
when speaker is silent.
Channel/Link Max
Hello Fred. This is Susan.
Do you have a minute?
Fred here. Hi!
Sure!
Conversation
Bandwidth used
Voice frames sent even when speaker is silent
Time
Channel/Link max
Tx
+
R
x
C
h
a
n
Ba
nd
wid
th
Tx
Rx
B
and
w
idth -
>
Bandwidth Used
Rx
Tx
Fred Here.
Hello Fred. This is Susan. Do you have a minute?
Time ->
Sure! Hi!
Rx
+
T
x
C
h
an
“Half-Duplex Call” alternates
use of half duplex bandwidth.
Channel/Link Max
Hello Fred. This is Susan.
Do you have a minute?
Fred here.
Hi! Sure!
Conversation
Bandwidth used
Half-duplex call alternates use of half duplex bandwidth
Time
Channel/Link max
T
x
+ Rx
Chan
Ba
nd
wid
th
Tx
Rx