Digitale Medien und Netze 1 rohc Robust Header Compression 50th IETF March 2001 Minneapolis Chairs: Carsten Bormann Mikael Degermark Mailing List:

Digitale Medien und Netze 2 50 th IETF: Agenda (from feet) u1. WG chair admonishments u2. Real agenda Blue sheets Scribe

Digitale Medien und Netze 3 Hello! This is an IETF Working Group uWe are here to make the Internet work (Fred Baker) s Together! (Harald Alvestrand) uRough Consensus and Running Code (Dave Clark) uWorking Group is controlled by s IETF Process (RFC2026, RFC2418) – read it! s Area Directors (ADs): Alison Mankin, Scott Bradner s Charter ( -- read it! s Working Group Chairs: Mikael Degermark, Carsten Bormann s Technical Advisor: Erik Nordmark uWork is done on list s And on IETF meetings, interim meetings, informal meetings, … s Mailing list is official channel, though

Digitale Medien und Netze 4 RFC 2026: Internet Standards Process uStandards track RFCs: s WG consensus (as judged by WG chairs) s WG last call s IESG approval (based on AD recommendation) s Quality control! s IETF last call uInformational RFCs uBCP (best current practice) RFCs

Digitale Medien und Netze 5 RFC 2026: IPR issues (1) u(10.2) No contribution that is subject to any requirement of confidentiality or any restriction on its dissemination may be considered […] uWhere the IESG knows of rights or claimed rights […] the IETF Executive Director shall attempt to obtain from the claimant […] a written assurance that upon approval by the IESG of the relevant Internet standards track specification(s), any party will be able to obtain the right to implement, use and distribute the technology […] based upon the specific specification(s) under openly specified, reasonable, non-discriminatory terms.

Digitale Medien und Netze 6 RFC 2026: IPR issues (2) uContributions (10.3.1(6)): “The contributor represents that he has disclosed the existence of any proprietary or intellectual property rights in the contribution that are reasonably and personally known to the contributor.” uI.e., if you know of a patent application for a technology you are contributing, you have to tell. Or just shut up entirely!

Digitale Medien und Netze 7 IPR issues: ROHC WG policy uIETF IPR policy defined in RFC2026 uFor expedience: Include IPR statements in the contributions (I-Ds, slides) s Upon advancement to RFC, these IPR statements will be replaced by a pointer to uUnencumbered technologies facilitate interoperability and are therefore generally preferable s Of two roughly equal proposals, select the unencumbered one s Desirable: Default configuration is unencumbered

Digitale Medien und Netze 8 ROHC: Charter (1) uCellular links: expensive, limited bandwidth uIP/UDP/RTP and IP/TCP packets benefit considerably from header compression uExisting schemes (RFC 1144, RFC 2508) s do not perform well over cellular: high error rates and long link roundtrip times s do not compress TCP options such as SACK or Timestamps uGoal of ROHC: s develop header compression schemes that perform well over links with high error rates and long roundtrip times. s must perform well for cellular links built using technologies such as WCDMA, EDGE, and CDMA s should also be applicable to other future link technologies with high loss and long roundtrip times s Ideally, it should be possible to compress over unidirectional links.

Digitale Medien und Netze 9 ROHC: Charter (2) uGood performance: s minimal loss propagation s minimal added delay uTarget: s generic TCP and UDP/RTP compression s applications of particular interest: voice and low-bandwidth video uROHC may develop multiple compression schemes s e.g., for specific link layer technologies s additional schemes may be added in consultation with the ADs. uMust: s assure that when a header is compressed and then decompressed, the result is semantically identical to the original; s perform well when end-to-end path involves more than one cellular link; s support IPv4 and IPv6. And, of course, the size…

Digitale Medien und Netze 10 ROHC: Charter (3) uFirst task: Create more thorough requirements documents uMaintain connections with other standardization organizations developing cellular technology for IP, such as 3GPP and 3GPP-2 s ensure that output fulfills their requirements and will be put to good use uDevelop a solid understanding of the impact that specific error patterns have on HC schemes, and document guidelines to L2 designers regarding what L2 features work best to assist L3/L4 HC uAddress interactions with IPSEC and other security implications. uRemember: Only IESG can change the charter!

Digitale Medien und Netze 11 ROHC: Charter (4) Goals and Milestones uMar: I-D on Requirements for IP/UDP/RTP HC. uMay: I-D of layer-2 design guidelines. uMay: I-D(s) proposing IP/UDP/RTP HC schemes. uMay: I-D of Requirements for IP/TCP HC. uJun: Requirements for IP/UDP/RTP HC submitted to IESG (Inf.) uJul: Requirements for IP/TCP HC submitted to IESG (Inf.) uJul: Resolve possibly multiple IP/UDP/RTP HC schemes into a single scheme. uAug: I-D on IP/TCP header compression scheme. uSep: Layer-2 design guidelines submitted to IESG (Inf.)  TCP g/l uSep: IP/UDP/RTP HC scheme submitted to IESG (PS) uDec: IP/TCP HC scheme submitted to IESG (PS) uJan: Possible recharter of WG to develop additional HC schemes. Done in last-call Start now To do

Digitale Medien und Netze 12 IPR approach uFree implementations can’t use licensing process s Neither can garage-based companies uBase spec should be unencumbered s IPR players agree to waive license for standard-based implementations uExamples of acceptable patent licenses: s RFC1822 license s

Digitale Medien und Netze th IETF: Agenda (1) u0900 Chair admonishments and agenda (10) u0910 WG document status(10) u0920 Testing and implementing RTP ROHC s 0920 News from ROHC field testing(10) s 0930 News from Siemens implementationWest (5) s 0935 Bay-Cough proposalPrice (5) u0940 ROHC over PPP Bormann (5) u byte s GPP2 reportJonsson (5) s 0950 RequirementsJonsson (12) s 1002 SolutionsJonsson (3) s 1005 WG work item?(3)

Digitale Medien und Netze th IETF: Agenda (2) u1008 TCP s 1008 RequirementsJonsson (12) s 1020 TAROC update Zhang (10) u1030 EPIC s 1030 EPIC updatePrice (5) s 1035 TCP (and SCTP) on EPIC updatePrice (10) s 1045 WG work item?(5) u1050 Signalling compression s 1050 RequirementsHannu (12) s 1102 SolutionsHannu (3) s 1105 WG work item?(5) u1110 Rechartering(20)

Digitale Medien und Netze 15 WG documents in publication: RTP ROHC uApproved by IESG on Feb 23 s RTP requirements (draft-ietf-rohc-rtp-requirements-05.txt) s Framework and four profiles (draft-ietf-rohc-rtp-09.txt) uAlready part of 3GPP Release 4 s Change Requests approved by TSG RAN last week s Alongside with R99’s inclusion of RFC2507 (not RFC2508!) uAdopted by 3GPP2 s Report at 0945

Digitale Medien und Netze 16 Lower layer guidelines udraft-ietf-rohc-rtp-lower-layer-guidelines-01.txt uCompleted WG last-call in December uStalled s AD input: Prescriptive text not in style for Informational s Did not attempt IETF last-call (to avoid stall for RTP ROHC!) uHow to proceed? s 0) force the issue :-) s 1) submit as BCP s 2) edit and submit as informational s 3) other?

Digitale Medien und Netze 17 ROHC over PPP udraft-ietf-rohc-over-ppp-01.txt uSon-of-2509 (PPP negotiation in IPCP) s Makes ROHC immediately useful in PPP world s Also: Example for negotiation needed by other types of links uChanges from –00 s Two-byte profile identifiers in negotiation s Two PPP protocol identifiers (1 small CIDs, 1 large CIDs) s Removed LARGE_CIDS flag uReady for WG last-call?

Digitale Medien und Netze 18 EPIC – how to use? uDo we want to take this up for further ROHC work? uNeed a way to use this in standards s Could standardize the output of the EPIC processor (duuh) s Define EPIC processor input language? uHard to do the all-layers trick here… s Will have to cooperate with other bodies s Are we the right body to “package” EPIC for them?

Digitale Medien und Netze 19 ROHC TCP – why develop separately? uThe requirements for robustness may be less stringent s Can do retransmission at link layer (see PILC) uLess stringent time constraints on development uDifferent protocol than RTP (obviously) uNew problems: Options like SACK, timestamps uSolicit wider input wrt next generation TCP compression s But is this maybe still a researchy topic?

Digitale Medien und Netze 20 ROHC TCP Requirements uDifferent link properties s No residual errors, but may have packet loss uRobustness: s Should not disable [might even help] TCP mechanisms s fast retransmit, fast repair, etc s MUST NOT generate damaged headers (that can pass TCP chksum!) s Must deal with current and future TCPs s SACK, timestamp, ECN, Diffserv, Initial TCP negotiation, etc s TCP sequence numbers and IP ID less predictable uMight want it to work well for short-lived TCP transfers? uSolve known problems with TCP Checksum s Window scale option – satellite links (loss of 64K undetectable) s window field decrement + seq no increment (rfc1144)

Digitale Medien und Netze 21 TCP ROHC requirements uAlready on ROHC charter! s But we didn’t get around to it, yet uThere is no TCP HC out there that does SACK, ECN, … s The world is looking at ROHC to fix this s Attempt to be future-proof! èROHC TCP must be applicable in the wide Internet s Encumbered solutions won’t cut it!

Digitale Medien und Netze 22 TCP – way forward? uNeed requirements document s How much can you guess about TCP implementations uNeed lower-layer guidelines document s How much L2 reliability is good for you? uStart work on TCP scheme s State management s Assume EPIC for encoding?

Digitale Medien und Netze 23 EPIC – make this a WG item? uPro: s Don’t have to carve out packet headers by hand any more s Provably optimal :-) uCon: s Implementation complexity? s Run-time overhead? s Remember ASN.1 PER? s Need interoperable implementations! s IPRs? uCan decide late in the TCP process…

Digitale Medien und Netze 24 Signaling compression – make it a WG item? uPro: s It’s needed! (Call setup time will be bad without it) s Fits in ROHC framework *if* done hop-by-hop s No changes to end systems, more redundancy to look at s Hop-by-hop makes it easier to compress between calls uCon: s Might be better done end-2-end (or in SIP proxy) s What about IPCOMP, TCPFILTER and friends? s Not really header compression (do we care?) s Is hop-by-hop still useful once SIP gets secure? s IPRs?

Digitale Medien und Netze 25 0-byte – way forward? uLots of confusion on what we are doing here s Distinguishing element: use synchronous, fixed frame channel s Allow for buffering in the compressor uArchitecture s (End) system “IP Stack” architecture s Protocol architecture uDoes it work in mid-path? uDocument limitations s E.g., non-transparent solution may not work with payload compression that uses SN/TS as initialization s vector s ECN bits, IP-ID, … on downlink side… RTCP… uIt seems we need a requirements delta document

Digitale Medien und Netze 26 Bay-Cough? uWe have one proposal: s Host: Siemens (Roke Manor) s Date: The week before IETF-51 ( to ) uTo do: Test sequences s Negotiation, mode transitions, state transitions, packet formats uTo do: Infrastructure, reference points uTo do: nail down any IPR issues

Digitale Medien und Netze 27 Rechartering: Goals and Milestones (1) uLower-layer Guidelines: submit for ____ RSN uROHC-over-PPP s WG last-call April 2001, submit May 2001 u0-byte IP/UDP/RTP s Try for 3GPP2 deadline (September 2001)? s Requirements and Assumptions: I-D April 2001 s WG last-call July 2001, submit August 2001 uUDP-lite profile? s Try for 3GPP deadline (December 2001)? s Requirements, Specification: I-Ds April 2001 s WG last-call August 2001, submit September 2001

Digitale Medien und Netze 28 Rechartering: Goals and Milestones (2) uEPIC s Need to be done before TCP if we want to use it for that s Decide: Interoperable implementations by Dec 2001? uTCP: new dates s Requirements and assumptions frozen: August 2001 (London) s draft-ietf-rohc-tcp-00.txt: September 2001 s WG last-call March 2002, submit April 2002 uSignaling compression s Focus on call-setup time issue s Requirements and assumptions draft: August 2001 s Start protocol work *if* we decide to go on (August 2001)

Digitale Medien und Netze 29 Rechartering: Goals and Milestones (3) uROHC over reordering channels??? uMIB s Initial I-D: October 2001 s WG last-call Jan 2002, submit Feb 2002 uDraft standard by 1Q2002 s Separate documents (Framework, 4 profiles): October 2001 s WG last-call Jan 2002, submit Feb 2002 uSCTP? s Leave for next rechartering (look again in London)

Digitale Medien und Netze 30 Rechartering (4) uRemember: This all has to go through the ADs…