SIP Functionality and Structure of the Protocol By

SIP – Functionality and Structure of the Protocol By Omar A. Abouabdalla Network Research Group (USM)

What is SIP ? ! SIP or Session Initiation Protocol is an application-level control protocol for setting up, changing and terminating multimedia sessions between participants on IP data networks. SIP is a text-based protocol, similar to HTTP and SMTP, for initiating interactive communication sessions between users. Such sessions include voice, video, chat, interactive games, and virtual reality.

When it Starts ? ! n n n The protocol's roots extend back to 1996. SIP was first developed within the Multiparty Multimedia Session Control (MMUSIC) working group at Internet Engineering Task Force (IETF). In 1999 SIP was approved as an official standard. In 1999 RFC 2543 was published. Its real value has only recently been uncovered.

How it Works ? ! n n SIP requires the use of user data gram protocol (UDP), and TCP is optional. SIP contains its own retransmission mechanisms for the purpose of establishing sessions. Session Description Protocol (SDP), which is the encoded body of the SIP message contains information about what media types the parties can and will use. Destinations in SIP are represented with Uniform Resource Indicators (URI), which have the same format as e-mail addresses.

SIP Advantages ? ! n n n It is short, simple and flexible protocol. It needs only a small set of messages and responses. Can run over most fixed and wireless networks. It uses the internet model and maps it onto telecom world. It uses email-like addresses to identify users. SIP address to identify users rather than the devices they happen to be using.

How it Functions ? ! SIP supports five facets of establishing and terminating multimedia communications: n n n User Location: determination of the end system to be used for communication. User Availability: determination of the willingness of the called party to engage in communications. User Capabilities: determination of the media and media parameters to be used. Session Setup: "ringing", establishment of session parameters at both called and calling party. Session Management: including transfer and termination of sessions, modifying session parameters.

How it Functions ? ! (cont’d. . ) SIP is a component that can be used with other IETF protocols to build a complete multimedia architecture. n n Real-time Transport Protocol (RTP) for transporting real time data. Real-time Streaming Protocol (RTSP) for controlling delivery of streaming media. The Media Gateway Control Protocol (MEGACO) for controlling gateways to Public Switched Telephone Network (PSTN). Session Description Protocol (SDP) for describing multimedia sessions.

Tan’s SIP Client penang. com proxy Bob’s SIP Client tokyo. com proxy INVITE F 1 100 Trying F 3 INVITE F 2 100 Trying F 5 180 Ringing F 8 200 OK F 11 180 Ringing F 7 200 OK F 10 ACK F 12 Media Session BYE F 13 200 OK F 14 INVITE F 4 180 Ringing F 6 200 OK F 9

SIP Methods n n n Invite - Indicates that the user is invited to a session. Ack - Used to confirm a session establishment. Bye - Terminates the sessions. Cancel - Used to cancel a pending Invite. Options - Used to query the server for its capabilities. Register - Used to bind a permanent address to the current location of the user.

SIP Responds Codes q 1## Informational Responses q 100 Trying q 180 Ringing q 181 Call is being forwarded q 2## Success q 200 OK q 3## Redirection q 300 Multiple Choices q 301 Moved Permanently q 302 Moved Temporarily

SIP Responds Codes (cont’d. . ) 4## Client Error q 400 Bad Request q 401 Unauthorized q 482 Loop Detected q 486 Busy Here q 5## Server Failure q 500 Server Internal Error q 6## Global Failure q 600 Busy Everywhere q

SIP Structure Transaction User (TU) Transaction Layer Client Component Server Component Transport Layer Syntax Layer

Conclusion SIP is short, simple and flexible signaling protocol for creating, modifying, and terminating sessions with one or more participants. Future work will be to bridge between SIP and other multimedia control protocols like RSW control protocol.

Thank You