An Introduction to SIP Moshe Sambol Services Research Lab November 18, 1998

GTE Laboratories SRL Presentation2 The Session Initiation Protocol §Communications protocol under development by the IETF’s MMUSIC working group. Last call for comments is over, SIP is about to become a standard. §Text-based IP application-layer protocol (derived from HTTP) for Internet multi-party multi-media conferencing establishment and management.

November 18, 1998GTE Laboratories SRL Presentation3 SIP Basics §Separation of call data and connection control l as opposed to PSTN: DTMF / pulses and on- hook/off-hook signals carried in band with call. §Carries service and participant information l provides natural support for advanced telephony services.

November 18, 1998GTE Laboratories SRL Presentation4 SIP Basics continued §Simpler language than H.323 supports flexibility, expandability, greater expression §Media and/or participants can be added to or removed from existing conferences §Supports personal mobility, degrees of security...

November 18, 1998GTE Laboratories SRL Presentation5 The SIP Call Model §Session: A set of multimedia senders and receivers and the data which flows between them. §Conference: A multimedia session identified by a session description. Composed of one or more calls. §Call: All participants in a conference invited by a single source. §Call Leg: All communication between one caller and callee within a call. §Transaction: All messages within a call leg from a first request until a final* response.

November 18, 1998GTE Laboratories SRL Presentation6 Actors in a SIP Conference §User Agent l Client application which initiates and accepts invitations; interacts with media applications. §SIP Proxy Server l Intermediary which relays requests after possible lookup and/or translation. §SIP Redirect Server l Maps a request to a set of alternate addresses and returns those to the client without initiating requests of its own.

November 18, 1998GTE Laboratories SRL Presentation7 SIP Actors, continued §Location Service l Not defined by SIP but used by its servers to locate other SIP servers. §No Gatekeeper l Gatekeeper traditionally provides admission control, address translation. These functions provided by other SIP actors.

November 18, 1998GTE Laboratories SRL Presentation8 SIP Operation in Proxy Mode All illustrations courtesy of H.Schulzrinne

November 18, 1998GTE Laboratories SRL Presentation9 SIP Operation in Redirect Mode

November 18, 1998GTE Laboratories SRL Presentation10 SIP Requests §REGISTER l Notify server of user location and availability §OPTIONS l Determine user capabilities §INVITE  CANCEL l Call setup Transaction termination §BYE l Call termination / transfer

November 18, 1998GTE Laboratories SRL Presentation11 SIP Responses §SIP Provides a rich set of response codes which make it well suited to support advanced telephony services: l 1xx: Provisional responses (ringing, queued, etc.) l 2xx: Final success responses l 3xx: Redirect responses (moved perm/temp, mult. choices, etc.) l 4xx: Client-Error (formatting, authorization, timeout, loop, etc.) l 5xx: Server-Error l 6xx: Global-Failure (busy, decline, does not exist, etc.)

November 18, 1998GTE Laboratories SRL Presentation12 An Example SIP Message INVITE SIP/2.0 Via: SIP/2.0/UDP kton.bell-tel.com From: A. Bell To: T. Watson Call-ID: Cseq: 1 INVITE Subject: Mr. Watson, come here. Content-Type: application/sdp Content-Length: … v=0 o=bell IN IP m=audio 3456 RTP/AVP

November 18, 1998GTE Laboratories SRL Presentation13 … Sample Response SIP/ Ringing Via: SIP/2.0/UDP kton.bell-tel.com From: A. Bell To: T. Watson Call-ID: Cseq: 1 INVITE Content-Length: SIP/ OK Via: SIP/2.0/UDP kton.bell-tel.com From: A. Bell To: T. Watson Call-ID: Cseq: 1 INVITE Contact: Content-Type: … m=audio 5004 RTP/AVP 0 3 …

November 18, 1998GTE Laboratories SRL Presentation14 Sample Services l Multi-party call transfers l generic addressing directed pick-up l multiple pick-up hold music control l third party call control camp-on l click to dial back availability notification §SIP Supports l Multicast UDP + TCP l Privacy (authentication, encryption, path hiding)

November 18, 1998GTE Laboratories SRL Presentation15 Transfer Example: Telemarketing

November 18, 1998GTE Laboratories SRL Presentation16 State of SIP §SIP implementations are being worked on at: l ObjectSoftware Nokia Research l Lucent Mediatrix l ISI HP Labs l GMD Fokus Ericsson l Dynamicsoft others? §My own graduate work was on...

November 18, 1998GTE Laboratories SRL Presentation17 Open Issues §Billing §Mappings to telephony APIs §Interfacing to external media applications §Location services Topics for Future Presentations §SIP vs. H.323  SDP §Security  Richer examples!

November 18, 1998GTE Laboratories SRL Presentation18 Additional Info At: §Professor Henning Schulzrinne: l l §Working group mailing list: l §Struggling ex-graduate student: l