Cisco SPA525G Administration Guide - Page 122

6 120 Configuring Security, Quality, and Network Features Ensuring Voice Quality 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 G.711 G.726-40 G.726-32 G.726-24 G.726-16 G.729 Est. Bandwidth Budget 110 kbps 87 kbps 79 kbps 71 kbps 63 kbps 55 kbps 2 Calls 220 kbps 174 kbps 158 kbps 142 kbps 126 kbps 110 kbps 4 Calls 440 kbps 348 kbps 316 kbps 284 kbps 252 kbps 220 kbps 6 Calls 660 kbps 522 kbps 474 kbps 426 kbps 378 kbps 330 kbps 8 Calls 880 kbps 696 kbps 632 kbps 568 kbps 504 kbps 440 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