Cisco MC3810-APM-FXO= Datasheet download pdf (Page 57)

Configuring Voice Ports

Configuring Digital Voice Ports

VC-91

Cisco IOS Voice, Video, and Fax Configuration Guide

Verifying DTMF Timer Inter-Digit Command

To verify the DTMF timer, use the following command in EXEC mode:

Voice Activity Detection Commands Related to Voice-Port Configuration Mode

In normal voice conversations, only one person speaks at a time. Today’s circuit-switched telephone

networks dedicate a bidirectional, 64 kbps channel for the duration of each conversation, regardless of

whether anyone is speaking at the moment. This means that, in a normal voice conversation, at least

50 percent of the bandwidth is wasted when one or both parties are silent. This figure can actually be

much higher when normal pauses and breaks in conversation are taken into account.

Packet-switched voice networks, on the other hand, can use this “wasted” bandwidth for other purposes

when voice activity detection (VAD) is configured. VAD works by detecting the magnitude of speech in

decibels and deciding when to cut off the voice from being framed. VAD has some technological

problems, however, which include the following:

• General difficulties determining when speech ends

• Clipped speech when VAD is slow to detect that speech is beginning again

• Automatic disabling of VAD when conversations take place in noisy surroundings

VAD is configured on dial peers; by default it is enabled. For more information, see the “Configuring

Dial Plans, Dial Peers, and Digit Manipulation” chapter in this configuration guide. Two parameters

associated with VAD, music threshold and comfort noise, are configured on voice ports.

If VAD is enabled, use the following commands to adjust parameter values associated with VAD,

beginning in voice-port configuration mode:

Command Purpose

Router# show running-config

Displays the configuration information currently

running on the terminal.

Command Purpose

Step 1

Router(config-voiceport)# music-threshold

number

Specifies the minimal decibel level of music

played when calls are put on hold. The decibel

level affects how voice activity detection (VAD)

treats the music data. Valid entries range from –70

to –30. When used with VAD, if the level is set too

high, the remote end hears no music; if it is set too

low, there is unnecessary voice traffic. The default

is –38.

Step 2

Router(config-voiceport)# comfort-noise

This parameter creates subtle background noise to

fill silent gaps during calls when VAD is enabled

on voice dial peers. If comfort noise is not

generated, the resulting silence can fool the caller

into thinking the call is disconnected instead of

being merely idle. The default is that comfort

noise is enabled.

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Cisco MC3810-APM-FXO= Datasheet Page 57

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