Session Initialization Protocol (SIP) Presented by: Lei Luo Computer & Information Science Department University of Delaware Nov. 18, 2004 Some slides are borrowed from Dorgham Sisalem’s SIP Tutorial

What Is SIP? Alice’s Home Station Alice Phone Network Bob

What is SIP? A signaling protocol Enable Internet endpoints Set up Modify Multimedia Sessions Tear down Request/deliver presence and Instant messages Enable Internet endpoints Discover one another Agree on a characterization of a session

What is NOT SIP? Not a transport protocol Not a media transmission protocol Not a QoS Reservation Protocol Not an integrated communications system

Internet Multimedia Protocol Stack SCTP Source: Henning Schulzrinne, http://www.cs.columbia.edu/~hgs/internet/

What can SIP Do? User Location User Availability User Capability Session Setup Session Management

What Else Can SIP Do? Request/deliver presence information and instant message sessions: Publish and upload presence information Request delivery of presence information Notify presence and other events Transport instant messages

Marconi Tesla INVITE 180 Ringing 200 OK ACK Media Session BYE 200 OK Simple SIP session establishment example

Proxy Server Bob Alice INVITE INVITE 180 Ringing 180 Ringing 200 OK 200 OK ACK Media Session BYE 200 OK SIP call example with proxy server

Alice Registrar Server REGISTER Contact: sip:alice@128.175.13.16 200 OK SIP registration example

SUBSCRIBE 200 OK NOTIFY 200 OK … NOTIFY 200 OK MESSAGE 200 OK MESSAGE 200 OK SIP presence and instant message example

How does SIP Work? Based on HTTP-like request/response model Text-based protocol Use the UTF-8 charset SIP message A request from a client to a server A response from a server to a client

SIP User Agent (UA) SIP-enabled end-devices Maintain states on calls Local and remote tags Call-ID Local and remote CSeq header fields Contain client (UAC) & server applications (UAS) Must support SDP for media description

SIP User Agent Examples Cisco Siemens MIC

Presence Agent SIP devices Collect presence information Receive subscription requests Generate state notifications Collect presence information Need to authenticate a subscription request

SIP Gateway A special type of UA Terminate the signaling path Interface a SIP network to a non-SIP network Terminate the signaling path May or may not terminate the media path Support much more users than normal UA

SIP Networks with Gateways Local/long distance 1-212-5551212 Telephone switch rtspd: media server Quicktime Single machine RTSP sipconf: Conference server RTSP clients Department PBX sipum: Unified messaging Internal Telephone Extn: 7040 713x Proxy, redirect, registrar server SQL database Web server SIP/PSTN Gateway Web based configuration SNMP (Network Management) Extn: 7134 Extn: 7136 H.323 SIP/H.323 Gateway xiaotaow@cs NetMeeting Borrowed from Xiaotao Wu’s slides (Columbia University, 2002)

SIP Servers  SIP Workhorses Logical Entities Accept SIP requests Respond to requests Types of Servers Proxy Server Redirect Server Registration Server

SIP Message Format Generic-message = Start-line *message-header CRLF [ message-body ] Start-line = Request-Line / Status-Line Request-Line = Method SP Request-URI SP SIP-Version CRLF Status-Line = SIP-Version SP Status-Code SP Reason-Phase CRLF SP – blank space

SIP Methods Sets Basic Methods Extended Methods INVITE REGISTER BYE ACK CANCEL OPTIONS Extended Methods REFER SUBSCRIBE NOTIFY MESSAGE etc.

SIP Response Codes Consistent with/extend HTTP/1.1 response codes 1xx – Informational 2xx – Success 3xx – Redirection 4xx – Client error 5xx – Server failure 6xx – Global Failure 600 – Busy Everywhere 603 – Decline 604 – Does Not Exist Anywhere etc. Borrowed from HTTP  Created for SIP

SIP Registration Server REGISTER sip:registrar.udel.edu Via: SIP/2.0/UDP 128.175.13.50:5060; branch=z9hG4bKus19 Max-Forwards: 70 To: Alice <sip:alice@eecis.udel.edu> From: Alice <sip:alice@eecis.udel.edu>;tag=3431 Call-ID: 23@128.175.13.50 CSeq: 1 REGISTER Contact: sip:alice@128.175.13.50 Content-Length: 0 Alice Registrar Server SIP/2.0 200 OK Via: SIP/2.0/UDP 128.175.13.50:5060; branch=z9hG4bKus19 To: Alice <sip:alice@eecis.udel.edu> From: Alice <sip:alice@eecis.udel.edu>;tag=3431 Call-ID: 23@128.175.13.50 CSeq: 1 REGISTER Contact: <sip:alice@128.175.13.50>;expires=3600 Content-Length: 0

SIP Proxy Server Location server DNS server Outbound proxy server INVITE sip:bob@yahoo.com SIP/2.0 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK83842.1 Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com> From: Alice <sip:alice@udel.edu>;tag=42 Subject: Where are you exactly? Contact: <sip:alice@pc.udel.edu> Location server DNS server INVITE sip:bob@yahoo.com SIP/2.0 Via: SIP/2.0/UDP proxy.yahoo.com:5060; branch=z9hG4bKtiop3 Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK83842.1 Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com> From: Alice <sip:alice@udel.edu>;tag=42 Subject: Where are you exactly? Contact: <sip:alice@pc.udel.edu> INVITE sip:bob@yahoo.com SIP/2.0 Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com> From: Alice <sip:alice@udel.edu>;tag=42 Subject: Where are you exactly? Contact: <sip:alice@pc.udel.edu> Outbound proxy server Inbound proxy server 100 Trying 180 Ringing 200 OK 100 Trying 180 Ringing 200 OK 180 Ringing 200 OK BYE ACK Media (RTP) Alice 200 OK Bob SIP Trapezoid

SIP Proxy Server INVITE Bob INVITE Bob Bob’s Phone 486 Busy Here Alice Proxy servers can make flexible “routing decisions” to decide where to send a request. Bob’s voicemail

SIP Proxy Server Bob’s Cell Phone INVITE Bob 200 OK INVITE Bob Bob’s Office Phone INVITE Bob CANCEL Alice 200 OK Bob’s Home Phone INVITE Bob CANCEL In parallel search, a proxy issues several requests to possible user locations upon receiving an incoming request.

SIP Redirect Server ACK Redirect Server Alice Bob SIP/2.0 302 Moved Temporarily Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com>;tag=64 From: Alice <sip:alice@udel.edu>;tag=42 Subject: Where are you exactly? Contact: sip:alice@200.201.202.203 INVITE sip:bob@yahoo.com SIP/2.0 Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com> From: Alice <sip:alice@udel.edu>;tag=42 Subject: Where are you exactly? Contact: <sip:alice@pc.udel.edu> ACK Redirect Server INVITE sip:bob@200.201.202.203 SIP/2.0 Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17a To: Bob <sip:bob@yahoo.com> From: Alice <sip:alice@udel.edu>;tag=13473 Subject: Where are you exactly? Contact: <sip:alice@pc.udel.edu> Alice Bob

That’s It! We have learned a lot about SIP!! No Way!!! Did we really learn a lot of stuff about SIP? Then what are we gonna do?

Key References J. Rosenberg, SIP: Session Initialization Protocol, RFC 3261, 2002 A. Johnston, SIP: Understanding the Session Initialization Protocol, 2nd edition J. Kuthan and D. Sisalem, SIP Tutorial http://iptel.org/sip/ SIP web site: http://www.cs.columbia.edu/sip/

Questions?