RFC2543 Rewrite: Enhancing Clarity and Structure for BIS-04 Normative Content

1. The new bis

2. 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

3. 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

4. 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

5. 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

6. New Structure • Transaction Layer • Reliability • Request/Response Matching • ACK generation for non-INVITE • Transaction Users • Manage dialog/session semantics • INVITE-200

7. Intro Overview of Functionality Terminology Overview of Operation Structure of the Protocol Definitions SIP Messages General UA Behavior Canceling Requests Registrations Querying for Capabilities Dialogs Initiating a Session Modifying a Session Terminating a Session Proxy Behavior Transactions Transport Security Common Message Components Headers Response Codes SRV Examples BNF Outline

8. 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. INVITE Client FSM |INVITE from TU Timer A fires |INVITE sent Reset A, V Timer B fires INVITE sent +-----------+ t.o. to TU +---------| |---------------+ | | Calling | | +-------->| |-------------->| +-----------+ 2xx | 300-699 | | 2xx to TU | ACK sent | |1xx | +---------------+ |1xx to TU | | | | | 1xx V Timer C fires | | 1xx to TU -----------+ t.o. to TU | | +---------| |-------------->| | | |Proceeding | | | +-------->| |-------------->| | +-----------+ 2xx | | 300-699 | 2xx to TU | | ACK sent, | | | resp. to TU| | | | | NOTE: | 300-699 V | | ACK sent +-----------+ | transitions | +---------| | | labeled with | | | Completed | | the event | +-------->| | | over the action | +-----------+ | to take | ^ | | | | | Timer D fires | +--------------+ | - | | | V | +-----------+ | | | | | Terminated|<--------------+ | | +-----------+

10. INVITE Server FSM |INVITE |pass to TU, send 100 INVITE V send response+-----------+ +--------| |--------+101-199 from TU | | Proceeding| |send response +------->| |<-------+ +-----------+ 300-699 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|<---------------+ | | +-----------+

11. 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

12. 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 Other changes

13. Big changes to –05 (so far) • CANCEL and ACK contain the same Route header fields as their associated request.

14. 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

15. 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

16. Robert Sparks +1.972.473.5467 sip:rjsparks@dynamicsoft.com mailto:rsparks@dynamicsoft.com Information Resource