rohc Robust Header Compression 49. IETF December 2000 San Diego

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rohc Robust Header Compression 49. IETF
December 2000San Diego

• Chairs
• Carsten Bormann ltcabo_at_tzi.OrggtMikael Degermark
  ltmicke_at_cs.Arizona.edugt
• Mailing List
• rohc_at_cdt.luth.se

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ROHCRObust Header Compression

• Header compression is prerequisite for all-IP
  wireless
• Wireless lossy, long latency (multiple packets
  in flight)
• Problem RFC2508 (CRTP) causes loss propagation
  on packet losses with long RTT links
• Basic idea
• No delta encoding!
• Expose (LSBs of) the RTP sequence number in the
  compressed packet key everything off that
• R-mode (reliable) Use ACKs to synchronize state
• O-mode (optimistic) Use CRCs to verify
  synchronization
• U-mode (unidirectional) Send info often enough

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ROHC WG

• Chairs Carsten Bormann (TZI), Mikael Degermark
  (U Arizona)
• http//www.dmn.tzi.org/ietf/rohc
• Work Items
• Robust Header Compression for IP/UDP/RTP
• Needed for e2e VoIP/video conferencing as well as
  streaming
• Transparent solution nearing completion (Dec 2000
  timeframe)
• Non-transparent extensions may follow
• Robust Header Compression for TCP
• Starting now (robustness can easily aided by L2
  retransmission)

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RTP ROHC document status WG last-call

• End-date 2000-12-14 about 1400Z
• draft-ietf-rohc-rtp-lower-layer-guidelines-00.txt
  (Oct 12)
• No last-call comments yet
• draft-ietf-rohc-rtp-requirements-03.txt (Nov 20)
• Few last-call comments
• draft-ietf-rohc-rtp-06.txt (Nov 29) RTP ROHC
• Main deliverable
• 156 pages
• 15 WG last-call comments so far

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ROHC Charter (4) Goals and Milestones
Done in last-call Start now To do

• Mar I-D on Requirements for IP/UDP/RTP HC.
• May I-D of layer-2 design guidelines.
• May I-D(s) proposing IP/UDP/RTP HC schemes.
• May I-D of Requirements for IP/TCP HC.
• Jun Requirements for IP/UDP/RTP HC submitted to
  IESG (Inf.)
• Jul Requirements for IP/TCP HC submitted to IESG
  (Inf.)
• Jul Resolve possibly multiple IP/UDP/RTP HC
  schemes into a single scheme.
• Aug I-D on IP/TCP header compression scheme.
• Sep Layer-2 design guidelines submitted to IESG
  (Inf.) ? TCP g/l
• Sep IP/UDP/RTP HC scheme submitted to IESG (PS)
• Dec IP/TCP HC scheme submitted to IESG (PS)
• Jan Possible recharter of WG to develop
  additional HC schemes.

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ROHC TCP why develop separately?

• The requirements for robustness may be less
  stringent
• Can do retransmission at link layer (see PILC)
• Less stringent time constraints on development
• Different protocol than RTP (obviously)
• 2507 is not enough Options like SACK, timestamps
• Need to compress ECN bits well!
• Solicit wider input wrt next generation TCP
  compression
• But is this maybe still a researchy topic?
• Two drafts right now
• draft-ietf-rohc-tcp-taroc-00.txt
• TCP over EPIC (distributed on mailing list)

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ROHC TCP Requirements

• Different link properties
• No residual errors, but may have packet loss
• Robustness
• Should not disable might even help TCP
  mechanisms
• fast retransmit, fast repair, etc
• MUST NOT generate damaged headers (that can pass
  TCP chksum!)
• Must deal with current and future TCPs
• SACK, timestamp, ECN, Diffserv, Initial TCP
  negotiation, etc
• TCP sequence numbers and IP ID less predictable
• Might want it to work well for short-lived TCP
  transfers?
• Solve known problems with TCP Checksum
• Window scale option satellite links (loss of
  64K undetectable)
• window field decrement seq no increment
  (rfc1144)

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Call for help

• ROHC TCP design will be influenced by link
  layers
• Loss rate, loss patterns, residual bit error
  rate, latency, latency distribution, queueing
  behavior, channel variants,
• ROHC TCP needs documented information on link
  layers
• What is out there that will be used below ROHC
  TCP
• What can we expect in the next 5 years
• In particular, what would be reasonable to build
• Link layer designers need information about ROHC
  TCP
• Document our assumptions so they know what to
  select
• ROHC TCP Lower Layer Guidelines Document
• (Help with the ROHC TCP scheme is appreciated,
  too)
• www.dmn.tzi.org/ietf/rohc