Supported Codecs - Cisco 501G Administration Manual

Configuring Security, Quality, and Network Features
Ensuring Voice Quality
Cisco SPA500 Series and WIP310 IP Phone Administration Guide

Supported Codecs

Negotiation of the optimal voice codec sometimes depends on the ability of the
Cisco IP Phone to "match" a codec name with the far-end device/gateway codec
name. Cisco IP phones allow the network administrator to individually name the
various codecs that are supported such that the correct codec successfully
negotiates with the far-end equipment.
Note that Cisco IP phones support voice codec priority. You can select up to three
preferred codecs.
The administrator can select the low-bit-rate codec used for each line. G.711a and
G.711u are always enabled. The following table shows the codecs supported by
Cisco IP phones. The third column shows the voice quality Mean Opinion Score
(MOS), with a scale of 1–5, in which higher is better.
Codec (Voice Complexity and Description
Compression
Algorithm)
G.711 (A-law Very low complexity. Supports uncompressed 64
and u-law) kbps digitized voice transmission at one through ten 5
ms voice frames per packet. This codec provides the
highest voice quality and uses the most bandwidth of
any of the available codecs.
G.726 Low complexity. Supports compressed 16, 24, 32, and
40 kbps digitized voice transmission at one through
ten 10 ms voice frames per packet. When no static
payload value is assigned per RFC 1890, Cisco IP
phones can support dynamic payloads for G.726.
NOTE
SPA525G.
G.729 and G.729A low-medium complexity. G.729 medium
G.729A complexity.
G.729A requires about half the processing power of
G.729. The G.729 and G.729A bit streams are
compatible and interoperable, but not identical.
G.726 is supported only for 32kbps on the
5
MOS Score
4.5
Highest
voice quality
4. 1 (32 kbps)
4
101