Linksys SPA 900 manual Technology Background, Session Initiation Protocol

Chapter 1 Introducing Linksys IP Phones

Technology Background

Table 1-4 Linksys Phone Features (continued)

Feature	Description
Voice Activity	Voice Activity Detection (VAD) with Silence Suppression is a means of
Detection with Silence	increasing the number of calls supported by the network by reducing the
Suppression and	required bidirectional bandwidth for a single call. VAD uses a very
Comfort Noise	sophisticated algorithm to distinguish between speech and non-speech
Generation	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	Linksys IP phones have three configurable interdigit timers:
with 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	Linksys IP phones report a variety of status and error reports to assist service
Event Logging	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	Linksys IP phones support detailed logging of all activities for further
Server Records	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	The statistics collected by Linksys IP phones during normal operation
Reporting	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.

Technology Background

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

•Session Initiation Protocol, page 1-9

	Linksys IP Phone Administrator Guide
1-8	Firmware Version 5.1