Nortel Networks NN43001-563 Speech Activity Detection, DTMF Through Dial

Dialing plans 69

Provisioned in TM 3.1 (in ms) Value used by IP Trunk 3.01

96 96

128 (default value in IP Trunk 3.01) 128 (default value in IP Trunk 3.01)

Speech Activity Detection

Speech activity detection reduces the IP bandwidth used by typical

voice conversations. When Speech Activity Detection is enabled, no

voice samples are sent during periods of silence (from one side of the

conversation or the other). When a caller stops speaking, instead of a

"dead" line, the listener hears "comfort noise" generated to match the

previous background noiselevel when the caller was speaking.

Coders can send silence frames before the end of transmission during a

period of silence. Coders might omit sending audio signals during periods of

silence after sending a single frame of silence, or send silence background

ﬁll frames, if these techniques are speciﬁed by the audio codec in use.

This background white noise keeps the telephone from sounding like the

line has gone dead - the listener can tell that the call is still up, and that

the person at the other end has merely stopped speaking. This technique

allows pauses during calls to sound almost the same as they would on a

standard telephone line. The primary beneﬁt of Speech activity detection is

that it allows the IP Trunkto use bandwidth only when it needs to send voice

samples, thereby saving expensiveWAN bandwidth for data trafﬁc or other

voice and fax calls. Since normal telephone conversations include pauses,

and only one side is normally speaking, Speech activity detection reduces

the bandwidth used on a call by more than half.

For applications that send no packetsdur ing silence,the ﬁrst packet after

a silence period is distinguished by setting a marker bit in the Real Time

Protocol (RTP) data header. Applications without Speech Activity Detection

set the bit to zero.

DTMF Through Dial

Preservation and transport of tones through the IP Trunk 3.01 (and later)

network is critical for Interactive VoiceResponse (IVR) services. IP Trunk

3.01 (and later) can be conﬁgured to ensure that DTMF tone information is

included in the packets that are sent through the IP Trunk 3.01 (and later)

network and that the tones are re-transmitted by the far-end gateway. The

duration information for DTMF signals is not transmitted; that is, long DTMF

bursts are reduced to a short standard duration.

Nortel Communication Server 1000

IP TrunkFundamentals

NN43001-563 02.01 Standard

Release 5.5 21December 2007