Mitel 5560 IPT none Specifications download pdf (Page 195)

Bandwidth, Codecs and Compression

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Other coding laws also exist. One that gives good voice quality and is also efficient at coding

is G.729. This also comes in different formats:

• G.729 - original version—very processor intensive

• G.729a - reduced processor effort and compatible with G.729

• G.729b - includes voice activity detection and ability to send background information. Com-

patible with G.729 and G.729a

Wideband audio, up to 7kHz (50Hz to 7.0kHz) of voice bandwidth, is available with the G.722

range of codecs. Although there are a number of wideband codecs under the G.722 banner a

number of these are not compatible with each other, so extra care is needed when specifying

these.

The wideband codec used by Mitel is G.722.1 at 32kbits/s/ (which is not to be confused with

the G.722 wideband codec, or the G.722.1C codec, or the G.722.1 at 24kbits/s).

Mitel currently uses the following CODECs in IP Telephony:

• G.711 (A-Law and µ-Law)

• G.729a

• G.722.1 at 32kbits/s

Voice quality and codec selection

The voice quality of the CODECs available is usually expressed in terms of a Mean Opinion

Score (MOS). The scores range in value from 1 to 5. Scores 4 and above are considered toll

quality. Table shows some typical CODEC MOS scores.

Codec selection

The CODEC to be used for a connection depends on a number of configurable parameters

including:

• Which Zone the network elements and devices are in

• Bandwidth Management - Call Admission Control Thresholds

• Network Zones - Intra-zone compression - Yes/No

CODEC G.729 is generally referred to as "compression" even though this is a generic term. CODEC

G.722.1 is generally referred to as "wideband" even though it also provides a bandwidth usage

improvement over G.711.

Table 56: CODEC MOS Scores

CODEC type MOS LAN bandwidth

G.711 4.4 ~100 kbit/s

G.729a 4.0 ~40 kbit/s

G.722.1 4.4 ~65 kbit/s

1 2 ... 190 191 192 193 194 195 196 197 198 199 200 ... 380 381

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Mitel 5560 IPT none Specifications Page 195