Learn just how easy it is to create a basic telecommunications application
using SIP servlets. The use of open standards such as SIP, together with Java
programming, has radically simplified the task of creating complex applications.
SIP and the SIP Servlet API
Learn just how easy it is to create a basic telecommunications application using Session Initiation Protocol (SIP) servlets. The use of open standards such as SIP, together with Java programming, has radically simplified the task of creating complex applications.
SIP is an application-layer protocol used to create and manage media sessions
between devices. These sessions are established and controlled through the use
of SIP messages. After establishing the sessions, any media can be exchanged,
although SIP does not concern itself with this aspect of the session. The SIP
RFC (3261) defines several key concepts and elements that can be found in a SIP
* A User Agent (UA) is an end-point that enables you to create and manage a
communication session. A UA can be a SIP telephone or a software application; it
is responsible for session setup and management tasks such as transfer,
termination, and service invocation. In addition, the UA can identify user
availability and negotiate session capability, that is, the media supported.
* A session is established by the UA (known as the caller) inviting another UA
(known as the callee) to join a communication session.
* A SIP message is a text-based entity, of which there are two types: requests
and responses. A request is sent from one UA to another, which in turn sends a
* A SIP Proxy Server is usually responsible for handling registrations,
implementing call-routing policies, and performing authentication and
authorization. Its most basic task is to ensure that a request is sent to
another entity closer to the targeted user. A proxy interprets, and, if
necessary, rewrites specific parts of a request message before forwarding it. A
SIP message might pass through several SIP Proxy Servers as it travels to the
callee UA. A UA is usually configured to send any requests it originates to a
specific SIP Proxy Server.
* A SIP address, or SIP URL, is used to uniquely identify a user and is used
during the creation of a communication session. It is very similar to an e-mail
address except that it has a sip: prefix. For example, the telephone on your
desk might have this SIP address sip:firstname.lastname@example.org.
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