Bandwidth Requirements - Cisco SPA942 - - IP Phone Administration Manual

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Bandwidth Requirements

Depending on how you have your IP phones configured, each call requires 55 to
110 kbps in each direction. Therefore, using G.729 as the voice codec setting, and
with an average business-grade broadband Internet connection supporting 1.5
Mbps downstream and 384 kbps upstream, a total of seven (7) simultaneous
conversations can be reliably supported with adequate bandwidth available for
file downloads.
Cisco recommends using the Cisco IP phones with QoS-capable networking
equipment that can prioritize the VoIP application traffic. QoS features are
available on many data networking switches and routers. A QoS-enabled router
prioritizes the packets going upstream to the ISP.
The following table approximates the bandwidth budget for each side of the
conversation (in each direction) using different codecs and number of calls. This
table is based on the following assumptions:
• Bandwidth calculated with no silence suppression
• 20 millisecond of payload per RTP packet
Codec Est.
Bandwidth
Budget
G.711 110 kbps
G.726-40 87 kbps
G.726-32 79 kbps
G.726-24 71 kbps
G.726-16 63 kbps
G.729 55 kbps
Configuring Security, Quality, and Network Features
2 Calls 4 Calls
220 kbps 440 kbps
174 kbps 348 kbps
158 kbps 316 kbps
142 kbps 284 kbps
126 kbps 252 kbps
110 kbps 220 kbps
NOTE: The use of silence suppression can
reduce the average bandwidth budget by 30%
or more.
Cisco SPA and Wireless IP Phone Administration Guide
Ensuring Voice Quality
6 Calls 8 Calls
660 kbps 880 kbps
522 kbps 696 kbps
474 kbps 632 kbps
426 kbps 568 kbps
378 kbps 504 kbps
330 kbps 440 kbps