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Robust Header Compression

Robust Header Compression. Mikael Degermar k <micke @ cs.arizona.edu> Co-chair, ROHC WG (to be) University of Arizona/ Ericsson Research. Mobile Terminal. Base Station. Base Station. Mobile Terminal. Cellular Link. Cellular Link. Wired Network. Robust header compression.

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Robust Header Compression

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  1. Robust Header Compression Mikael Degermark <micke @ cs.arizona.edu> Co-chair, ROHC WG (to be) University of Arizona/ Ericsson Research

  2. Mobile Terminal Base Station Base Station Mobile Terminal Cellular Link Cellular Link Wired Network Robust header compression • Goal: Making IP-telephony as speech service economicallyviable compared to traditional circuit switched telephony.

  3. Link properties • Wireless cellular networks usually run at a point where there is around 1% frame loss. • Raw bit-error rate 10 • %, after channel coding, etc, 1e-2 to 1e-6. • Voice codecs can cope with such loss and still deliver reasonable service. • A loss event involves 1-2 packets. For some technologies 3. Longer events very rare. • True for WCDMA, GSM, CDMA-2000, EDGE.

  4. IP voice packet 40+8+12+24 20+8+12+24

  5. compression point decompression point destination source feedback context 1144 VJ: implicit 2508 CRTP: link-local 2507 IPHC: optional link-local context HC exploits regularities in stream of headers. Schemes above suffer under high-loss & irregularities. “twice”

  6. Requirements • Complete transparency • No production of erroneous headers • No added packet loss due to header compr. • IPv6, IPv4, RTP/UDP/IP, TCP/IP • Extension headers, TCP options • RTP for voice & video • Compress headers of tunneled packets • Should be possible to compress over simplex links.

  7. Most loss due to context damage • Large delay-bandwidth product over link • Unrepaired context damage implies loss of entire “window” , i.e., 100-200 ms of voice. • So, avoid context damage or repair without going across link. • ROCCO: repair without going across link • ACE: delta in compressed header is relative to hdr confirmed to have reached decompressor

  8. Robust header compression • Avg. header size less than 2 bytes. • Minimal header is one byte • Both ROCCO and ACE • Neither add significantly to loss rate. • No reliance on transport checksums • May not be present. • Voice codecs might want data even if damaged. • Entirely possible to do similar things for TCP.

  9. Tunneling & Security • Encypted or authentication data cannot be compressed. (AH adds significantly) • Outer header in an encrypted tunnel can be compressed (IPHC, rfc2507) • Inner headers could be compressed at tunnel entry point, but currently no defined way to do so for transport headers. • Reordering. • Work in AVT, but may not perform well enough when RTP stream subject to high loss.

  10. Compression of inner headers for end-to-end encryption. for tunnels across “core network” Need robustness against reordering & loss & irregularities in packet stream. work in AVT, but may not produce robust solution Compression of signaling packets? Further information rohc @ cdt.luth.se draft-degermark-crtp-eval-01.{txt, ps} draft-degermark-robhc-requirements-00.txt draft-jonsson-robust-hc-03.{txt, ps} Rfcs 1144, 2507-2509

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