27 February 2008

The bandwidth needed for VoIP transmission will depend on a few
factors: the compression technology, packet overhead, network protocol
used and whether silence suppression is used. This tip investigates the
first three considerations. Silence suppression will be covered in a
later tip.

There are two primary strategies for improving IP network
performance for voice: Allocate more VoIP bandwidth (reduce
utilization) or implement QoS.

How much bandwidth to allocate depends on:

• Packet size for voice (10 to 320 bytes of digital voice)
• CODEC and compression technique (G.711, G.729, G.723.1, G.722, proprietary)
• Header compression (RTP + UDP + IP), which is optional
• Layer 2 protocols, such as point-to-point protocol (PPP), Frame Relay and Ethernet
• Silence suppression/voice activity detection