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SIP, Session Initiation Protocol

SIP, Session Initiation Protocol. Internet Draft, IETF, RFC 2543. Outline. Introduction SIP Components SIP Role SIP Addressing, Naming, Locating, Messages Request and Response Method SIP Services. Introduction.

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SIP, Session Initiation Protocol

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  1. SIP, Session Initiation Protocol Internet Draft, IETF, RFC 2543

  2. Outline • Introduction • SIP Components • SIP Role • SIP Addressing, Naming, Locating, Messages • Request and Response Method • SIP Services

  3. Introduction • The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants. • Include Internet multimedia conferences, Internet telephone calls and multimedia distribution.

  4. Introduction (con’d) • Interoperability • Between Multiple Equipment Vendors • Client-Server Model • Extensibility • Text-based Encoding • Transport Independence • UDP or TCP

  5. SIP Components • User Agents • Being end systems that act on behalf of a user • Clients(UAC) to initiate a SIP request and servers(UAS) to receive the request and return responses • Servers • Proxy • Redirect • Registrar: tracking user locations

  6. SIP Proxy SIP MGC MGC IP Network MEGACO/ MGCP MEGACO/ MGCP RTP MG MG PSTN PSTN SIP Role

  7. Addressing and Naming • The entities addressed by SIP are users at hosts (SIP URL) • email-like identifier of the form user@host • Examples • sip:kehung@vc.cs.nthu.edu.tw • sip:operator@cs.columbia.edu

  8. Locating • Server • IP address • name@domain-> DNS • User • Proxy server • It can send the request in sequence or in parallel to the locations listed. • Redirect server • It can return a response with the list placed in contact headers. • Then the client can send directly to the uses location.

  9. SIP Messages • Two kinds of SIP messages • Request and Response • The generic-message format • Start-line • Method, SIP Version,... • Headers • An Empty Line • Indicating the end of the header fields • Message Body • Session Description Protocol (SDP) : Optional

  10. Header Fields • General • Apply to both request and response messages • Entity • Define information about the message body • Request • Allow the client to pass additional information about the request • Response • Allow the server to pass additional information about the response

  11. SIP Headers

  12. Request Method • INVITE • The user is being invited to participate in a session. • ACK • The client has received a final response to an INVITE. • BYE • The client wishes to release the call. • CANCEL • It cancels a pending request (not completed request). • REGISTER • It conveys the user’s location information to a SIP server.

  13. Request Example INVITE sip:cycho@vc.cs.nthu.edu.tw SIP/2.0 Via: SIP/2.0/UDP tpts7.seed.net.tw From: <sip:kuann@seed.net.tw> To: C.Y.Cho <sip:cycho@vc.cs.nthu.edu.tw> Call-ID: 0926225561@tpts7.seed.net.tw Cseq: 1 INVITE Content-Length: …

  14. Response Messages

  15. Response Example SIP/2.0 200 OK Via: SIP/2.0/UDP vc.cs.nthu.edu.tw Via: SIP/2.0/UDP tpts7.seed.net.tw From: Fingal <sip:kuann@seed.net.tw> To: Patric <sip:cycho@vc.cs.nthu.edu.tw> Call-ID: 0926225561@tpts7.seed.net.tw Cseq: 1 INVITE Content-Type: applcation/sdp Content-Length: …

  16. Invitation for SIP Proxy

  17. Invitation for Redirect Server

  18. SIP Services • Similar to the Intelligent Network (IN) services • Call Transfer, Call Forwarding, Conference Calling, User Mobility…

  19. SDP • Session Description Protocol • It includes: • Session Name and purpose • Time (the session is active) • The media comprising the session • How to receive those media (e.g. addresses, ports, formats and so on). • Additional information can be • The bandwidth to be used by the conference

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