RFC 3095 (rfc3095) - Page 2 of 168


RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed



Alternative Format: Original Text Document



RFC 3095               Robust Header Compression               July 2001


   This is done in a framework designed to be extensible.  For example,
   a scheme for compressing TCP/IP headers will be simple to add, and is
   in development.  Headers specific to Mobile IPv4 are not subject to
   special treatment, but are expected to be compressed sufficiently
   well by the provided methods for compression of sequences of
   extension headers and tunneling headers.  For the most part, the same
   will apply to work in progress on Mobile IPv6, but future work might
   be required to handle some extension headers, when a standards track
   Mobile IPv6 has been completed.

Table of Contents

   1.  Introduction....................................................6
   2.  Terminology.....................................................8
   2.1.  Acronyms.....................................................13
   3.  Background.....................................................14
   3.1.  Header compression fundamentals..............................14
   3.2.  Existing header compression schemes..........................14
   3.3.  Requirements on a new header compression scheme..............16
   3.4.  Classification of header fields..............................17
   4.  Header compression framework...................................18
   4.1.  Operating assumptions........................................18
   4.2.  Dynamicity...................................................19
   4.3.  Compression and decompression states.........................21
   4.3.1.  Compressor states..........................................21
   4.3.1.1.  Initialization and Refresh (IR) State....................22
   4.3.1.2.  First Order (FO) State...................................22
   4.3.1.3.  Second Order (SO) State..................................22
   4.3.2.  Decompressor states........................................23
   4.4.  Modes of operation...........................................23
   4.4.1.  Unidirectional mode -- U-mode..............................24
   4.4.2.  Bidirectional Optimistic mode -- O-mode....................25
   4.4.3.  Bidirectional Reliable mode -- R-mode......................25
   4.5.  Encoding methods.............................................25
   4.5.1.  Least Significant Bits (LSB) encoding .....................25
   4.5.2.  Window-based LSB encoding (W-LSB encoding).................28
   4.5.3.  Scaled RTP Timestamp encoding .............................28
   4.5.4.  Timer-based compression of RTP Timestamp...................31
   4.5.5.  Offset IP-ID encoding......................................34
   4.5.6.  Self-describing variable-length values ....................35
   4.5.7.  Encoded values across several fields in compressed headers 36
   4.6.  Errors caused by residual errors.............................36
   4.7.  Impairment considerations....................................37
   5.  The protocol...................................................39
   5.1.  Data structures..............................................39
   5.1.1.  Per-channel parameters.....................................39
   5.1.2.  Per-context parameters, profiles...........................40
   5.1.3.  Contexts and context identifiers ..........................41



Bormann, et al.             Standards Track