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 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.

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

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

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

Addressing and Naming The entities addressed by SIP are users at hosts (SIP URL) – -like identifier of the form Examples

Locating Server –IP address 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.

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

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

SIP Headers

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.

Request Example INVITE SIP/2.0 Via: SIP/2.0/UDP tpts7.seed.net.tw From: To: C.Y.Cho Call-ID: Cseq: 1 INVITE Content-Length: …

Response Messages

Response Example SIP/ OK Via: SIP/2.0/UDP vc.cs.nthu.edu.tw Via: SIP/2.0/UDP tpts7.seed.net.tw From: Fingal To: Patric Call-ID: Cseq: 1 INVITE Content-Type: applcation/sdp Content-Length: …

Invitation for SIP Proxy

Invitation for Redirect Server

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

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