1. SIP Session Initiation Protocol Short Introduction Artur Hecker, ENST

2. SIP: Motivation Need for a signalization protocol New applications with the same needs:  IP telephony, video conferencing How can you:  address the opponent?  find the opponent?  negotiate parameters?  manage the session?

3. SIP: Alternative visions ITU-T: H.323 recommendation  The first and most deployed vision  Different versions since 1996 (the recent - V3)  Defines the whole suite of components with the roles, codecs, interactions, etc.  HEAVY! Megaco: MGCP  Multimedia Gateway Control Protocol  RFC 2705

4. SIP: RFC 2543 Application-layer signaling protocol for:  Session creation/modification/termination  Parameter set agreement  User mobility by proxying and redirecting  Current location registration SIP is:  Transport layer independent  Text-based and related to existent protocols (inheritance of SMTP and HTTP elements)

5. SIP: Main principles Internet-protocol: client-server Messages and headers follow the HTTP and SMTP schemes  Client sends requests, server answers with state responses (HTTP-like)  Addressing uses the familiar format: sip:sales@example.com Simplicity, transparency  Designed to be an “easy protocol”

6. SIP: Components Listen at the default port UDP/5060 Can optionally use TCP SIP-Clients:  UAC+UAS SIP-Servers:  Proxy  Registration Server  Redirect Server

7. SIP: Simple call scenario sip:chef@enst.frsip:oups@enst.fr UACUAS INVITE sip:oups@enst.fr SIP/2.0 1 ACK sip:oups@enst.fr SIP/2.0 SIP/2.0 200 OK 2 3 BYE sip:oups@enst.fr SIP/2.0 4 media session

8. SIP: Messages (1) SIP/2.0 200 OK Via: SIP/2.0/UDP rois.enst.fr From: P. Chef To: Call-ID: 1234567@rois.enst.fr CSeq: 1 INVITE Contact: sip:pauvre@travail.enst.fr Content-Type: application/sdp Content-Length: … v=0 o=pauvre 14234 41322 IN IP4 … s=Je suis en vacances c=IN IP4 travail.enst.fr m=audio 6043 RTP/AVP 0 3 INVITE sip:oups@enst.fr SIP/2.0 Via: SIP/2.0/UDP rois.enst.fr From: P. Chef To: M. Pauvre Call-ID: 1234567@rois.enst.fr CSeq: 1 INVITE Subject: Venez dans mon bureau Content-Type: application/sdp Content-Length: … v=0 o=chef 5432 7654 IN IP4 10.1.1.1 s=Venez dans mon bureau c=IN IP4 rois.enst.fr m=audio 1050 RTP/AVP 0 3 4 5 1 2

9. SIP: Messages (2) ACK sip:pauvre@travail.enst.fr SIP/2.0 Via: SIP/2.0/UDP rois.enst.fr From: P. Chef To: M. Pauvre Call-ID: 1234567@rois.enst.fr CSeq: 1 ACK BYE sip:pauvre@travail.enst.fr SIP/2.0 Via: SIP/2.0/UDP rois.enst.fr From: P. Chef To: M. Pauvre Call-ID: 1234567@rois.enst.fr CSeq: 2 BYE 4 3

10. SIP: Methods INVITE  invitation to a session, dialogue and session updates ACK  response confirmation to INVITE OPTIONS  query the server for its possibilities BYE  release the call CANCEL  Cancel the pending request REGISTER  Registration of a new location at some registration server

11. SIP: Response classes 1xx: Informational  In-call-setup informational responses 2xx: Success  Succeeded, done, accepted 3xx: Redirection  Further action needed to complete request 4xx: Client Error  Bad syntax or request can’t be fulfilled at the server 5xx: Server Error  Server can’t fulfill a valid request 6xx: Global Failure  The request can’t be fulfilled at any server

12. SIP: Headers Usage and meaning depend on the method Value according to syntax and current context Different categories:  general, entity, request, response  end-to-end and hop-by-hop Examples: Hide Encryption Expires Proxy-Authenticate Proxy-Authorization WWW-Authenticate

13. SIP: Components: Registration & Redirect Servers INVITE sip:chef@rois.enst.fr 302 Moved temporarily Contact: patrick@travail.enst.fr:3080;transport=udp REGISTER sip:register.enst.fr SIP/2.0 Via: SIP/2.0/UDP travail.enst.fr From: sip:chef@enst.fr To: sip:chef@enst.fr Call-ID: 12314@travail.enst.fr CSeq: 1 REGISTER Contact: Expires: 3600 register travail enst.fr

14. SIP: Components: General proxy SIP - trapezoid INVITE sip:some@lip6.fr Via: SIP/2.0/UDP rois.enst.fr enst.fr lip6.fr INVITE sip:some@lip6.fr Via: SIP/2.0/UDP proxy.enst.fr Via: SIP/2.0/UDP rois.enst.fr INVITE sip:sb@mobile.lip6.fr Via: SIP/2.0/UDP sip.lip6.fr Via: SIP/2.0/UDP proxy.enst.fr Via: SIP/2.0/UDP rois.enst.fr sip proxy rois mobile

15. SIP: Security Authentication  Basic: clear text password  Digest: challenge/response with MD5  PGP: using PK cryptography Encryption  e2e of the message body and some fields  hbh entire packet encryption  hbh of the Via: fields to hide the route

16. SIP: Presence & Future Problems:  Dialogue and session: no clear separation, INVITE used to adjust both states (will be changed in the new RFC)  No early media (UPDATE method)  Security problems: PGP hardly used, digest not proven to be secure, basic has severe problems (S/MIME, TLS, IPSec currently widely discussed, SIP-EAP draft released)  Routing: too strict (Loose Routing proposed in the new draft)  etc. New RFC expected till the middle of March  It will be the largest RFC ever released… Simple?

17. SIP: more… Handley et al., Session Initiation Protocol, RFC 2543 S. Donovan, The INFO Method for SIP, RFC 2976 IETF, SIP Working Group Charter, http://www.ietf.org/html.charters/sip-charter.html http://www.ietf.org/html.charters/sip-charter.html IETF, SIPPING Working Group Charter, http://www.ietf.org/html.charters/sipping-charter.html http://www.ietf.org/html.charters/sipping-charter.html J. Rosenberg et al., Session Initiation Protocol, draft-ietf-sip-rfc2543bis-09.txt A. Johnston et al., SIP Call Flow Examples, draft-ietf-sip-call-flows-05.txt