Cisco MC3810-APM-FXO= Datasheet download pdf (Page 11)

Configuring Voice Ports

Analog Voice Ports Configuration Task List

VC-45

Cisco IOS Voice, Video, and Fax Configuration Guide

Configuring Codec Complexity for Analog Voice Ports on the Cisco MC3810

with High-Performance Compression Modules

The term codec stands for coder-decoder. A codec is a particular method of transforming analog voice

into a digital bit stream (and vice versa) and also refers to the type of compression used. Several different

codecs have been developed to perform these functions, and each one is known by the number of the

International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) standard

in which it is defined. For example, two common codecs are the G.711 and the G.729 codecs. The various

codecs use different algorithms to encode analog voice into digital bit-streams and have different bit

rates, frame sizes, and coding delays associated with them. The codecs also differ in the amount of

perceived voice quality they achieve. Specialized hardware and software in the digital signal processors

(DSPs) perform codec transformation and compression functions, and different DSPs may offer different

selections of codecs.

Select the same type of codec as the one that is used at the other end of the call. For instance, if a call

was coded with a G.729 codec, it must be decoded with a G.729 codec. Codec choice is configured on

dial peers. For more information, see the “Configuring Dial Plans, Dial Peers, and Digit Manipulation”

chapter in this configuration guide.

Codec complexity refers to the amount of processing power that a codec compression technique

requires: some require more processing power than others. Codec complexity affects call density, which

is the number of calls that can take place on the DSP interfaces, which can be HCMs, port adapter DSP

farms, or voice cards, depending on the type of router (in this case, the Cisco MC3810 multiservice

concentrator). The greater the codec complexity, the fewer the calls that can be handled.

Codec complexity is either medium or high. The difference between medium- and high-complexity

codecs is the amount of CPU power necessary to process the algorithm and, therefore, the number of

voice channels that can be supported by a single DSP. All medium-complexity codecs can also be run in

high-complexity mode, but fewer (usually half as many) channels will be available per DSP.

For details on the number of calls that can be handled simultaneously using each of the codec standards,

refer to the entries for the codec and codec complexity commands in the Cisco IOS Voice, Video, and

Fax Command Reference.

On a Cisco MC3810 concentrator, only a single codec complexity setting is used, even when two HCMs

are installed. The value that is specified in this task affects the choice of codecs available when the codec

dial-peer configuration command is configured. See the “Configuring Dial Plans, Dial Peers, and Digit

Manipulation” chapter in this configuration guide.

Note On the Cisco MC3810 with high-performance compression modules, check the DSP voice channel

activity with the show voice dsp command. If any DSP voice channels are in the busy state, the codec

complexity cannot be changed. When all the DSP channels are in the idle state, changes can be made

to the codec complexity selection.

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Cisco MC3810-APM-FXO= Datasheet Page 11