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Voice Feature Guide 01

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Codec and Packetization Duration

Codec and Packetization Duration

Introduction

Codec is a key technology of voice services. Coding means that the DSP encodes the TDM-based voice data, assembles the data into packets, and then sends the packets to the IP network. Decoding means that the DSP decodes the voice packets received from the IP network and plays the voice to the TDM side.

Frequently-used codec types are G.711A, G.711Mu, G.729a, G.729b, G.726, G.723.1Low, and G.723.1High. G.711A and G.711Mu are lossless coding schemes. G.729, G.723.1Low, and G.723.1High are lossy compressed coding schemes. The compressed coding schemes require less bandwidth, but the voice quality is poor and the delay is large. (G.711 delivers the best voice quality but requires a bandwidth of 64 kbit/s. G.723 requires less bandwidth but the voice quality is less satisfying.)

PTime is the interval at which the DSP assembles the voice data into packets. It varies according to the codec type. Table 1-15 lists the codec types.

Table 1-15 Codec list

Codec Type

Coding Rate (kbit/s)

PTime

G.711A/G.711Mu

64

10 ms, 20 ms, 30 ms

G.729a/G.729b

8

10 ms, 20 ms, 30 ms

G.726

16/24/32/40

10 ms, 20 ms, 30 ms

G.723.1

5.3/6.3

30 ms, 60 ms

Standards and Protocols Compliance

ITU-T G.711, ITU-T G.729, ITU-T G.726 and ITU-T G.723

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Updated: 2019-02-22

Document ID: EDOC1100067358

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