SIP & its application

What is SIP (Session Initiation Protocol) ?

• A signaling protocol for setting up multimedia sessions between endpoints .• SIP is end-to-end, client-server session signaling protocol

similar to HTTP.• SIP designed in line with other Internet protocols by the

IETF.

SIP Basic Functionality

Supports 5 facets of communication:• User location: determination of the end system to be used for

communication; • User capabilities: determination of the media and media

parameters to be used;• User availability: determination of the willingness of the

called party to engage in communications; • Call setup: "ringing", establishment of call parameters at both

called and calling party; • Call handling: including transfer and termination of calls.

SIP Deployment Architecture

SIP Entities

• User Agent (UA) User Agent Client (UAC) – initiates a SIP request User Agent Server (UAS) – handles and eventually sends a response to a request• Proxy server – routing of SIP requests• Registar server – registration of user's contact addresses• Location server – providing of user location details• Redirect server – return callee's addresses to caller• Application server – providing advanced services for users

SIP Request Syntax

SIP methods• INVITE :initiate call• ACK :confirm final response• BYE :terminate (and transfer) call• CANCEL: cancel searches and “ringing”• OPTIONS: features support by other side• REGISTER: register with location service• INFO: mid-call information (ISUP)• COMET :precondition met• PRACK: provisional acknowledgement• SUBSCRIBE: subscribe to event• NOTIFY: notify subscribers• REFER: ask recipient to issue SIP request (call transfer)

SIP Response Syntax

  The response types

• 1xx - Provisional response• 2xx - Successful response• 3xx - Redirect response• 4xx - Client error• 5xx - Server error• 6xx - Global error

Via Field in Header• The Request headers include a Via field• The Via field indicates the path taken by the request so

far. • Every proxy adds a Via Header with its address to make

sure that responses within a transaction take the same path (to avoid loops, or to make sure that same firewall will be hit on the way back)

• This prevents request looping and ensures replies take the same path as the requests.

SIP Transaction• User agent A contacts

DNS server to map domain name in SIP request to IP address.

• User agent A sends a INVITE message to proxy server that uses location server to find the location of user agent B.

• Call is established between A and B. Then media session begins.

• Finally, B terminates the call by sending a BYE request

SIP Registration

SIP Proxying

SIP Redirection

Instant Messaging and SIMPLE• Session Initiation Protocol for Instant Messaging

and Presence Leveraging Extensions.• Instant messaging (IM) ,the most common and

popular methods of communicating over IP networks.• IM applications:-

■ AIM, America Online Instant Messenger ■ Google talk ■ Yahoo Messenger ■ MSN Messenger

WHAT IS VOIP

• Voice over IP (VoIP) is any technology that facilitates the voice communication and video conferencing uses live images and sound, over an IP network, such as the Internet.

• The two (or more) endpoints - often referred to as terminals or clients - could be any device with a microphone and speaker, such as a normal PC computer or something resembling a traditional phone.

• Session Initiation Protocol (SIP) is standard used in Voice over IP (VoIP).

VoIP APPLICATIONS

VoIP APPLICATIONS

References• RFC 2543: “SIP: Session Initiation Protocol” http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc2543.html • Papers on IP Telephony

http://www.cs.columbia.edu/~hgs/sip/papers.html • http://www.iptel.org/sip• http://www.cs.columbia.edu/sip/• http://www.iptel.org/sip/

Thank You