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Header Compression Schemes. Different Header Compression schemes. Compressed TCP – Van Jacobsen RFC 1144 only for TCP/IP for wired networks Perkins improvement for of CTCP IPHC only for IP protocol no feedback. General Structure of Header Compressors.

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different header compression schemes
Different Header Compression schemes
  • Compressed TCP – Van Jacobsen RFC 1144
    • only for TCP/IP
    • for wired networks
  • Perkins
    • improvement for of CTCP
  • IPHC
    • only for IP protocol
    • no feedback
general structure of header compressors
General Structure of Header Compressors
  • Two entities: compressor and decompressor
  • Compressor sends initial base
  • Base is used by compressor and decompressor
  • Compressor removes redundancy
  • Decompressor adds removed information
  • Proposed solution differ in a possible feedback channel

Base

Base

Decompressor

Compressor

N

N

N*

ctcp van jacobsen
CTCP (Van Jacobsen)
  • TCP/IP header compression
  • Using delta compression
  • Designed for wired networks
  • Not robust against error-prone links
  • Base update with each new incoming packet
loosing synchronization
Loosing synchronization
  • Synchronization loss = decompressor’s copy of the base is different from the compressor’s copy
  • Synchronization is lost any time a packet is dropped
  • Detection: using detection of TCP retransmissions. All retransmissions are sent uncompressed
performance of vj scheme in case of random errors
Performance of VJ scheme in case of random errors

Throughput of bulk data transfers

File sizes of 344K, 328K, and 550K

Kbytes/s

S. J. Perkins and M. W. Mutka, Dependency Removal for Transport Protocol Header Compression over Noisy Channels. 1997.

  • When synchronization is lost, the decompressor starts to toss packets  base update more often than needed
perkins refinement of ctcp
Perkins – Refinement of CTCP
  • Perkins & Mutka – improvement of CTCP in case of noise presence
  • Differentials are sent against a base that changes infrequently  packet loss does not cause endpoints to loose synchronization
  • All packets refer to the first packet of the frame
  • the same mechanisms can be used to detect loss of synchronization
perkins refinement of ctcp1
Perkins – Refinement of CTCP
  • Base refresh (sending uncompressed header) – to combat overflow problems
  • Robustness introduced by periodically repetition of full base information each N packets
  • N packets define a frame
  • Larger overhead
    • Less compression due to higher delta values
    • Additionally, 1 byte of CID (connection identifier) is transmitted
performance of perkins scheme
Performance of Perkins scheme

Throughput of bulk data transfers

File sizes of 344K, 328K, and 550K

S. J. Perkins and M. W. Mutka, Dependency Removal for Transport Protocol Header Compression over Noisy Channels. 1997.

ip header compression iphc
IP Header Compression (IPHC)
  • Provides extensions to VJ
    • Support UDP, IPv6,
    • Additional TCP features
  • Uses delta encoding
twice algorithm
TWICE algorithm
  • TCP header compression reduces throughput over lossy links
    • Bandwidth is wasted when unharmed segments are retransmitted after a timeout
  • Possible solutions:
    • Perkins algorithm
    • TWICE algorithm
twice algorithm1
TWICE algorithm
  • Decompressor can detect loss of synchronization by using TCP checksum
  • Motivation: totally lossless HC is not possible, make an educated guess
  • If inconsistency is due to a single lost segment + lost segment increments the compression state in the same way 
  • Apply TWICE the delta of a current segment
compressed rtp crtp
Compressed RTP (CRTP)
  • Compressed RTP (RFC 2508)
    • Compresses 40 byte header to 4 or 2 bytes
    • First-order changes
      • Expected changes in the fields that can be predicted, no transmission of differences needed
    • Second-order changes
      • Changes that have to be compressed
  • Enhanced Compressed RTP (RFC 3545)
    • Refinement of CRTP in presence of packet loss, reordering and long delays
    • Local retransmissions and repeated context updates are used
robust checksum based compression rocco
Robust Checksum-based Compression (ROCCO)
  • Refinement of CRTP
  • Includes checksum over uncompressed header  facilitation of local recovery of the synchronization
  • Targeted to cellular usage
robust header compression
Robust Header Compression
  • RTP/UDP/IP
  • UDP/IP
  • IP
  • uncompressed
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