Session Initiation Protocol (SIP)

Overview

SIP gaining with application service providers (Asps), communication service providers (CSPs), Network service providers (NSPs) for new IP based services. -

SIP is a “Text based protocol” similar to HTTP and SMTP, for initiating interactive communication session between users. -

SIP provides seamless transmission of voice, data, fax, and interactive games. -

What is SIP?

SIP – A protocol that allows voice, data, fax, video, instant messaging and even online gaming to be integrated with web-based application.

The SIP is an application –layer control protocol for creating, modifying and terminating session with one or more participants.

SIP History

SIP has origins in late 1996 as a component of the “Mbones” set of  utilities and protocols. -

SIP was designed with certain assumption.

Scalability

Component reuse

           

                        A Internet Engineering Task Force(IETF) standards, SIP is an open, internet genuine protocol for establishing and managing multi party, mixed media sessions over converged networks.

SIP Functionality & Basic Operation

SIP is about initiation interactive communication session between users. It also handles termination and modifications of sessions as well.

            * Locating the user , Inviting the user for session, Delivering the session description, Terminate the session.

SIP can invite both person and “robot”, such as a media storage service.

SIP can invite both parties to both unicast and multicast sessions. -

Session can be advertised using multicast protocol such as SAP, E-Mail, News group, web pages or directories.

SIP transparently supports name mapping and redirection services, allowing implementation of ISDN and intelligent network telephony subscriber services.

Person mobility

Terminal mobility

SIP supports 5 facts of establishing and terminating multimedia communications:

User Location -> Determination of the end system to be used for communication

User Capabilities -> Determination of the media and parameters to be used.

User Availability ->Determination of the willingness of the called parties to engage in communication.

Call Setup -> “Ringing”, establishment of call parameter of both called and calling parties.

Call Handling -> Including transfer and termination of calls.

Initiating a session

delivering a description

convey the response

 modify the session

A call consistent of all participates in a conferences invited by a common source. A SIP call is identified by a global unique call ID

A point to point internet telephony conversation maps into a single SIP call

SIP can 3 different multiparty conferencing architecture :

Full Mesh ->In a mesh participant builds a signaling with every other participant & sent an individual copy of the media stream to the others.

Mixers -> A mixers or bridge takes several media streams & replaces them to all participates.

N/W layer multicast -> Neither full mesh nor mixers scale to large conferences. These are most efficiently supported by n/w layer multicast.

Basic Architecture

User Agents

Proxy, Proxy server

Redirect server

Registrar

SIP Operation

Callers and callee are identified by SIP addresses.

SIP Addressing

Locating a SIP server

SIP Transaction

SIP Invitation

Locating the user

Changing an existing Session

Registration Services

SIP Properties

Minimal State

Lower-Layer-Protocol Neutral

It can provide packet or byte stream services with reliable or unreachable services.

TCP used, SIP can use ne or more connections to attempts to contact a user or modify parameter of an existing conference.

Text Based

Allows implementation in language such as java, Tcl and Perl.

Allows debugging and makes SIP flexible and extensible

SIP URL & SIP Message

SIP URL

Used within SIP message

embedded in web pages or other hyperlinks

When used as hyperlink it indicated by INVITE method.

SIP Message Overview

Senders must terminate line with CRLF and receivers must also interpret CR and LF.

SIP –Message=Request | Response

Both messages consist of a start line, one or more headers, an empty line and an optional message body.

Generic-Message = Start-Line * Message-                                                     Header CRLF [Message-                                                                                Body]

Start-Line=Request-Line | Status-Line

Message-header=(general-header | Request-header                            | Response-header | entity-header)

SIP Message Body

Message Body Type

Message Body Length

Security

Encryption

Message Integrity and Access Control : Authentication

Callee Privacy