NEC Univerge SV9100, Manual

Page: 324 / 766

Issue 2.0
5-12 Network Design Considerations
5.2 Bandwidth
The bandwidth required for VoIP calls depends on several factors, including:

Number of simultaneous calls

CODEC used
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Frame Size
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Data Networking Protocol used

UNIVERGE SV9100 CCIS Network parameters
The more frames encapsulated into each packet, the less bandwidth is required.
This is because each packet transmitted has the same header size. Therefore, if
numerous very small packets are sent then bandwidth is also being used for a
large amount of header information. If we add several frames to the packet, less
packets are transmitted and therefore have less header information sent.
If we add many voice frames to each packet, less bandwidth is being used.
However, this does have disadvantages. If there is a large packet size, and a
particular voice packet is lost, this has a greater impact on the speech quality. If a
small quantity of voice frames per packet is being used, the effect of losing a
packet is reduced.
As a general rule: The more frames per packet, the less bandwidth is used, but
the quality is also lower.
Examples:
Example 1: CODEC: G.729 Frame Size: 10ms Voice Frames per Packet: 2 Voice
Sample Size: 20ms (frame size x Voice Frames) Bandwidth Required: 24Kbps
Example 2: CODEC: G.729 Frame Size: 80ms Voice Frames per Packet: 8 Voice
Sample Size: 80ms (frame size x Voice Frames) Bandwidth Required: 12Kbps