Linksys SPA 900 Benutzerhandbuch

This section provides background information about the technology and protocols used by the phone:

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.