HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

SIP Stack 25
Feature Support
connection. This frequently causes a pair of SIP entities to use one connection
for requests sent in each direction, and can result in potential scaling and
performance problems. The Connection Reuse draft tries to solve this by adding
an alias parameter in the Via header. This parameter tells the application on the
remote side to map the existing connection for future requests from the original
side.
The SIP Stack version 4.0 implements the Connection Reuse draft and enables
heavily loaded applications to save connection ports and make faster
connections.
PARSING TEL, PRES
AND IM URIS
A SIP address can be described in several formats called URIs. A “tel” URI is a
way to describe a SIP endpoint using its phone number. A “pres” URI is a SIP
address used for Presence user agents (UAs). An “im” URI is used for instant
messaging. Each URI can appear in many variations and therefore the parsing of
these URIs is not a simple task.
The SIP Stack version 4.0 frees application developers from the task of parsing
these URIs. The SIP Stack handles any form of the URIs and hands the data to
the application in a friendly data structure.
SERVICE-ROUTE AND
PATH HEADERS
The information is transmitted in the initial REGISTER (or after roaming),
using Path and Service-Route headers.
The SIP Stack version 4.0 enables the encoding and decoding of the Path and
Service-Route headers.
SIP SESSION TIMER The Session Timer extension enables SIP servers and endpoints to know if an
endpoint is no longer in a session (for example in case of a crash) and to limit
the duration of a session. An endpoint that has the Session Timer extension
activated will send periodic keep-alive messages to notify that it is active or to
extend the duration of the session.
REPLACES HEADER The Replaces extension defines a new header for use with SIP multi-party
applications and call control. The Replaces header is used to logically replace an
existing SIP dialog with a new SIP dialog. This primitive can be used to enable a
variety of features, such as Attended Transfer and Retrieve from Call Park.
EXTENSIBILITY The SIP Stack provides rich extensibility capabilities that allow the application
developer to easily implement any number of the many extensions to SIP. These
include:
 General URL scheme support—general framework to support
any type of URL scheme, such as IM: and TEL:.