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

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. What is SIP ?! 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 ?! The protocol's roots extend back to The protocol's roots extend back to SIP was first developed within the Multiparty Multimedia Session Control (MMUSIC) working group at Internet Engineering Task Force (IETF). 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 SIP was approved as an official standard. In 1999 RFC2543 was published. In 1999 RFC2543 was published. Its real value has only recently been uncovered. Its real value has only recently been uncovered.

How it Works ?! SIP requires the use of user data gram protocol (UDP), and TCP is optional. 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. 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. 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 addresses. Destinations in SIP are represented with Uniform Resource Indicators (URI), which have the same format as addresses.

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

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

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

200 OK F14 BYE F13 Media Session ACK F OK F OK F OK F9180 Ringing F8 180 Ringing F7 180 Ringing F6 100 Trying F3 100 Trying F5 INVITE F1 INVITE F2 INVITE F4 Tan’s SIP Client Bob’s SIP Client penang.com proxy tokyo.com proxy

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

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

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

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

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

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