3Com NBX, Installation Manual

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Bandwidth Requirements 231
Bandwidth
Requirements
The interconnect bandwidth requirements depend on the selected audio
compression and system configuration [Layer 2 or Layer 3 (IP)] topology.
NBX default audio settings deliver optimum audio quality. Any change to
default audio settings affects audio quality.
Layer 2 Mulaw
(G.711) Audio
(Normal Setting)
The interconnection bandwidth requirements for a device configured as a
Layer 2 device running G.711 audio for each party in a conversation
requires a maximum of 73 Kbps. Thus, a point-to-point call requires this
peak bandwidth in each direction, while a 3-party conference requires a
peak of 219 Kbps in one direction. For more information, see
“Notes on
Bandwidth Requirements” later in this appendix.
Layer 3 Mulaw
(G.711) Audio
The overhead for running a device as a Layer 3 device results in a
maximum bandwidth requirement of 86 Kbps per party in the
conversation. Thus, a point-to-point call requires this peak bandwidth in
each direction, while a 3-party conference requires a peak of 258 Kbps in
one direction. For more information, see
“Notes on Bandwidth
Requirements” later in this chapter.
Layer 2 ADPCM Audio
(Reduced Bandwidth
Setting)
The interconnection bandwidth requirements for a device configured as a
Layer 2 device running ADPCM audio for each party in a conversation
requires a maximum of 42 Kbps. Thus, a point-to-point call requires this
peak bandwidth in each direction, while a 3-party conference requires a
peak of 126 Kbps in one direction. For more information, see
“Notes on
Bandwidth Requirements” later in this chapter.
Layer 3 ADPCM Audio
(Reduced Bandwidth
Setting)
The overhead for running a device as a Layer 3 device results in a
maximum bandwidth requirement of 54.7 Kbps per party in the
conversation. Thus, a point-to-point call requires this peak bandwidth in
each direction, while a 3-party conference requires a peak of 164 Kbps in
one direction. See
“Notes on Bandwidth Requirements” next.
Notes on Bandwidth
Requirements
Silence suppression reduces bandwidth requirements on average by 30 to
40 percent. However, do not assume this much bandwidth reduction
when determining peak requirements. These bandwidth reduction values
do not include link overhead (packet encapsulation, additional bytes for
error detection/correction, etc.) which may be added by the specific
interconnection device. This overhead is not under the control of the NBX
system, but must be added based upon the device specification.