The new bis

9 th SiPiT 4 Dec 2001 Why rewrite the specification? IESG said so RFC2543 was never the model of clarity to begin with Bis got worse with micro-editing Symptoms Repitition of material in many places No overview of operations Structure not obvious Decision made at August IETF to move forward full steam with a rewrite Goal: Preserve bis-04 normative content

9 th SiPiT 4 Dec 2001 How was it done? Recruited a bis rewrite team Jonathan, Henning editors Added four co-authors to help write Gonzalo Camarillo (Ericsson) Jon Peterson (Neustar) Alan Johnston (Worldcom) Robert Sparks (dynamicsoft) Coaching from Dean Willis, Brian Rosen Project Management from Rakesh Shah Technical writing from Jean Mahoney Jonathan prepared new outline and defines mapping of existing text to new outline (early Sep.) Sections assigned to each writer

9 th SiPiT 4 Dec 2001 How was it done? Iterative approach utilizing bugzilla and cvs First rewrite of each section done mid-September Several cycles of cross section review and revision Detailed verification of preservation of MUST/MAY/SHOULD Brutally painful! Deviations captured in changes section bis-05 complete and submitted 10/26/01

9 th SiPiT 4 Dec 2001 New Structure Semantically oriented Present SIP as a layered protocol Message layer Transport layer Transaction layer Transaction users Message layer Self explanatory – message formats Transport layer Manages persistent connections Listens for requests and responses Via rules for sending responses, inserting received param

9 th SiPiT 4 Dec 2001 New Structure Transaction Layer Reliability Request/Response Matching ACK generation for non-INVITE Transaction Users Manage dialog/session semantics INVITE-200

9 th SiPiT 4 Dec 2001 Outline 1. Intro 2. Overview of Functionality 3. Terminology 4. Overview of Operation 5. Structure of the Protocol 6. Definitions 7. SIP Messages 8. General UA Behavior 9. Canceling Requests 10. Registrations 11. Querying for Capabilities 12. Dialogs 13. Initiating a Session 14. Modifying a Session 15. Terminating a Session 16. Proxy Behavior 17. Transactions 18. Transport 19. Security 20. Common Message Components 21. Headers 22. Response Codes 23. SRV 24. Examples 25. BNF

9 th SiPiT 4 Dec 2001 Transport Layer Changes ACK-200 is officially a different transaction ACK non-200 is part of the transaction Same EXACT transaction machine for proxies and UA Handling for INVITE 2xx response *NOT* part of the transaction layer!! UA state machinery retransmits 2xx and ACK Allows transaction machines to die instantly when 2xx received Transitions based on timeouts, not # of retransmits, to unify machine between UDP, TCP More aggressive transaction timeouts defined for TCP Proper RTT estimation defined Actual diagrams for non-INVITE transactions included

9 th SiPiT 4 Dec 2001 INVITE Client FSM |INVITE from TU Timer A fires |INVITE sent Reset A, V Timer B fires INVITE sent t.o. to TU | | | | Calling | | >| | >| xx | | | 2xx to TU | ACK sent | |1xx | |1xx to TU | | | | | 1xx V Timer C fires | | 1xx to TU t.o. to TU | | | | >| | | |Proceeding | | | >| | >| | xx | | | 2xx to TU | | ACK sent, | | | resp. to TU| | | | | NOTE: | V | | ACK sent | transitions | | | | labeled with | | | Completed | | the event | >| | | over the action | | to take | ^ | | | | | Timer D fires | | - | | | V | | | | | | Terminated|< | |

9 th SiPiT 4 Dec 2001 INVITE Server FSM |INVITE |pass to TU, send 100 INVITE V send response | | from TU | | Proceeding| |send response >| |< from TU | |2xx from TU send response | |send response | | | INVITE V Timer G fires | send response send response | | | | | | Completed | | | >| |< | | | | | ACK | | | - | >+ | Timer H fires | V fail to TU | | | | | | Confirmed | | | | | | | | |Timer I fires | |- | | | V | | | | | | Terminated|< | |

9 th SiPiT 4 Dec 2001 Dialogs Equivalent to call-leg from bis-04 Call leg has been eradicated from the spec Generalization, presence Dialog procedures are no longer INVITE specific Maintenance of CSeq, Route sets Construction of mid-dialog requests General construction guidelines

9 th SiPiT 4 Dec 2001 Other changes Collected BNF BNF now uses explicit LWS Responses no longer need to transmitted over TCP for server transactions! Does NOT include INV-2xx CANCEL can’t be sent until 1xx received BYE can’t be sent by UAS until ACK received CR or LF alone deprecated 3xx to re-INVITE allowed and specified Radical surgery on multicast No special treatment at ALL except deciding where to send the messages Assumes only a single respondent If there are more than one, responses look like retransmits Still needs more refinement in spec Proxies no longer forward 6xx on receipt CANCEL first, then 6xx after all responses Merged requests detected only at endpoints Serverfeatures integrated 100rel will be integrated SDP extracted to a separate I-D

9 th SiPiT 4 Dec 2001 Big changes to –05 (so far) CANCEL and ACK contain the same Route header fields as their associated request.

9 th SiPiT 4 Dec 2001 What’s not stable? SRV functionality will change Under discussion with IESG Likely to be much simplified (no merging of transports) Route/Record-Route Loose routing Additional rigor and explanatory text needed Registration section Security section

9 th SiPiT 4 Dec 2001 Next steps Closing open issues Explicitly called out in bis-05 where possible Currently all being tracked in Bugzilla 49 open issues, vast majority are minor Major open issues: Loose source routing, proxy route processing Multicast operation Maximum messages sizes SRV Target completion to send to IESG before 2002

Information Resource Robert Sparks