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Linksys ATA Administration Guide
48
Silence Suppression and Comfort Noise Generation
Configuring Voice Services
(e)). This is available only for FSK-based CID methods: (Bellcore, ETSI FSK, and ETSI FSK
With PR).
•
Off Hook Caller ID — This is used to delivery caller-id on incoming calls when the
attached phone is off hook (see the following figure). This can be call waiting caller ID
(CIDCW) or to notify the user that the far end party identity has changed or updated
(such as due to a call transfer). This is available only for FSK-based CID methods:
(Bellcore, ETSI FSK, and ETSI FSK With PR).
Silence Suppression and Comfort Noise Generation
Voice Activity Detection (VAD) with Silence Suppression is a means of increasing the number of
calls supported by the network by reducing the required bandwidth for a single call. VAD uses a
sophisticated algorithm to distinguish between speech and non-speech signals. Based on the
current and past statistics, the VAD algorithm decides whether or not speech is present. If the
VAD algorithm decides speech is not present, the silence suppression and comfort noise
generation is activated. This is accomplished by removing and not transmitting the natural
silence that occurs in normal two-way connection. The IP bandwidth is used only when
someone is speaking. During the silent periods of a telephone call, additional bandwidth is
available for other voice calls or data traffic because the silence packets are not being
transmitted across the network.
Comfort Noise Generation provides artificially-generated background white noise (sounds),
designed to reassure callers that their calls are still connected during silent periods. If Comfort
Noise Generation is not used, the caller may think the call has been disconnected because of
the “dead silence” periods created by the VAD and Silence Suppression feature.
Silence suppression is configured in the Line and PSTN Line tabs. See
”Linksys ATA Routing Field
Reference,” on page 86
.
Polarity
Reversal
First
Ring
CAS
(DTAS)
DTMF/
FSK
Polarity
Reversal
CAS
(DTAS)
FSK
CAS
(DTAS)
Wait For
ACK
FSK
First
Ring
FSK
OSI
FSK
a) Bellcore/ETSI Onhook Post-Ring FSK
d) Bellcore Onhook FSK w/o Ring
f) Bellcore/ETSI Offhook FSK
c) ETSI Onhook Pre-Ring FSK/DTMF
e) ETSI Onhook FSK w/o Ring
DTMF
b) ETSI Onhook Post-Ring DTMF
First
Ring