Linksys SPA 900 - Manual (Page 19)

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Linksys IP Phone Administrator Guide
Firmware Version 5.1
Chapter 1 Introducing Linksys IP Phones
Technology Background
Technology Background
This section provides background information about the technology and protocols used by the phone:
• Session Initiation Protocol, page 1-9
Voice Activity
Detection with 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 bidirectional bandwidth for a single call. VAD uses a very
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.
Configurable Dial Plan
with Interdigit Timers Linksys IP phones have three configurable interdigit timers:
• Initial timeout (T)—Handset off hook; no digit pressed yet.
• Long timeout (L)—One or more digits pressed, more digits needed to
reach a valid number (as per the dial plan).
• Short timeout (S)—Current dialed number is valid, but more digits
would also lead to a valid number.
Report Generation and
Event Logging Linksys IP phones report a variety of status and error reports to assist service
providers in diagnosing problems and evaluating the performance of their
services. The information can be queried by an authorized agent, using
HTTP with message-digest authentication, for instance. The information
may be organized as an XML page or HTML page.
Syslog and Debug
Server Records Linksys IP phones support detailed logging of all activities for further
debugging. The debug information may be sent to a configured Syslog
server. Linksys IP phones provide configuration settings that determine the
type of activity/events that should be logged as, for example, a debug level
setting.
Dynamic Payload When no static payload value is assigned per RFC 1890, Linksys IP phones
can support dynamic payloads for G.726.
Call Statistics and
Reporting The statistics collected by Linksys IP phones during normal operation
statistics are available in the Info tab. Line status is reported for each line (1
and 2). Each line maintains up to 2 calls: Call 1 and 2.
Table 1-4 Linksys Phone Features (continued)
Feature Description