Configuring Security, Quality, and Network Features
Ensuring Voice Quality
120 Cisco SPA and Wireless IP Phone Administration Guide
6
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
2 Calls 4 Calls 6 Calls 8 Calls
G.711 110 kbps 220 kbps 440 kbps 660 kbps 880 kbps
G.726-40 87 kbps 174 kbps 348 kbps 522 kbps 696 kbps
G.726-32 79 kbps 158 kbps 316 kbps 474 kbps 632 kbps
G.726-24 71 kbps 142 kbps 284 kbps 426 kbps 568 kbps
G.726-16 63 kbps 126 kbps 252 kbps 378 kbps 504 kbps
G.729 55 kbps 110 kbps 220 kbps 330 kbps 440 kbps
NOTE: The use of silence suppression can
reduce the average bandwidth budget by 30%
or more.
To Next Page
Loading...
Need help?
General
