SIP is a signaling protocol used to set up multimedia communication sessions between endpoints over IP networks. It allows for user location, capabilities, availability, call setup and handling. SIP uses client-server architecture with user agents, proxies, registrars, and other entities. Common SIP methods include INVITE, ACK, BYE, and REGISTER. Responses are categorized by class with 1xx for provisional, 2xx for success, 3xx for redirect, 4xx for client error, 5xx for server error, and 6xx for global errors. The Via header tracks the path of SIP requests. SIP supports voice and video calls as well as instant messaging through extensions like SIMPLE.

1. SIP & its application

2. 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.

3. 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.

4. SIP Deployment Architecture

5. 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

6. SIP Request Syntax

7. 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)

8. SIP Response Syntax

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

10. 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.

11. 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

12. SIP Registration

13. SIP Proxying

14. SIP Redirection

15. 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

16. 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).

17. VoIP APPLICATIONS

18. VoIP APPLICATIONS

19. 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/

20. Thank You