Operation Manual

AT-RG213 Residential VoIP Gateway - SIP Software Reference Manual
SIP Software Release 6-0-0
J613-M0524-00
44
(LDAP), to authenticate users (RADIUS, DIAMETER), and to scale to meet
the anticipated growth curves.
SIP is described as a control protocol for creating, modifying and
terminating sessions with one or more participants. These sessions include
Internet multimedia conferences, Internet (or any IP Network) telephone
calls and multimedia distribution. Members in a session can communicate
via multicast or via a mesh of unicast relations, or via a combination of these.
SIP supports session descriptions that allow participants to agree on a set of
compatible media types. It also supports user mobility by proxying and
redirecting requests to the userʹs current location. SIP is not tied to any
particular conference control protocol.
In essence, SIP has to provide or enable the following functions:
Name Translation and User Location
Ensuring that the call reaches the called party wherever they are located.
Carrying out any mapping of descriptive information to location
information. Ensuring that details of the nature of the call (Session) are
supported.
Feature Negotiation
This allows the group involved in a call (this may be a multi-party call) to
agree on the features supported – recognizing that not all the parties can
support the same level of features. For example video may or may not be
supported; as any form of MIME type is supported by SIP, there is plenty of
scope for negotiation.
Call Participant Management
During a call a participant can bring other users onto the call or cancel
connections to other users. In addition, users could be transferred or placed
on hold.
Call feature changes
A user should be able to change the call characteristics during the course of
the call. For example, a call may have been set up as ‘voice-only’, but in the
course of the call, the users may need to enable a video function. A third
party joining a call may require different features to be enabled in order to
participate in the call
Protocol Components
There are two components within SIP. The SIP User Agent and the SIP
Network Server. The User Agent is effectively the end system component for
the call and the SIP Server is the network device that handles the signaling
associated with multiple calls.
The User agent itself has a client element, the User Agent Client (UAC) and
a server element, the User Agent Server (UAS.) The client element initiates
the calls and the server element answers the calls. This allows peer-to-peer
calls to be made using a client-server protocol.