Network Working Group L-E. Jonsson
INTERNET-DRAFT Ericsson
Expires: April 2003 October 28, 2002
RObust Header Compression (ROHC):
A Compression Profile for IP
<draft-ietf-rohc-ip-only-00.txt>
Status of this memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This document is a submission of the IETF ROHC WG. Comments should be
directed to the ROHC WG mailing list, rohc@ietf.org.
Abstract
The original RObust Header Compression (ROHC) RFC, RFC 3095, defines
a framework for header compression, along with compression protocols
(profiles) for IP/UDP/RTP, IP/ESP, IP/UDP, and also for uncompressed
packet streams. However, no profile was defined for compression of IP
only, which has been identified as a flaw in RFC 3095. This document
addresses that problem and defines a ROHC compression profile for IP,
similar to the IP/UDP profile defined by RFC 3095, but simplified to
exclude UDP.
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Table of Contents
1. Introduction..................................................2
2. Terminology...................................................2
3. ROHC IP Compression (Profile 0x0004)..........................3
4. Security Considerations.......................................4
5. IANA Considerations...........................................4
6. References....................................................4
7. Author's Address..............................................4
1. Introduction
The original RObust Header Compression (ROHC) RFC [RFC-3095] defines
a framework for header compression, along with compression protocols
(profiles) for IP/UDP/RTP, IP/ESP, IP/UDP, and also for uncompressed
packet streams. The profile for uncompressed data was defined to
provide means to encapsulate all traffic over a link within ROHC
packets. Through this profile, the lower layers do not have to
provide multiplexing for different packet types, but instead ROHC can
handle any packet stream, even if compression profiles for all kinds
of packet streams have yet not been defined or implemented over the
link.
Although the profile without compression is simple and can tunnel
arbitrary packets, it has of course a major weakness in that it does
not compress the headers at all. When considering that normally all
packets are expected to be IP [RFC-791, RFC-1883] packets, and that
the IP header often represent a major part of the total header, a
useful alternative to no compression would for most packets be
compression of the IP header only. Unfortunately, such a profile was
not defined in [RFC-3095], and this has thus been identified as an
important missing piece in the ROHC toolbox.
This document addresses this missing compression support and defines
a ROHC compression profile for IP [RFC-791, RFC-1883] only, similar
to the IP/UDP profile defined by [RFC-3095], but simplified to
exclude UDP. Due to the similarities with the IP/UDP profile, the IP
compression profile is described based on the IP/UDP profile, mainly
covering differences.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC-2119].
ROHC UDP
"ROHC UDP" in this document refers to the IP/UDP profile
(Profile 0x0002) as defined in [RFC-3095].
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3. ROHC IP Compression (Profile 0x0004)
In principle, there is no real difference between the ROHC UDP
profile and the IP profile defined in this document, since the
removal of UDP does not at all effect the compression mechanisms. As
for ROHC UDP, the compressor generates a 16-bit sequence number which
increases by one for each packet compressed in the packet stream,
called SN or IP SN below. Unless stated explicitly below, mechanisms
and formats are as for ROHC UDP.
3.1. Initialization
The static context for ROHC IP compression can be initialized in
either of two ways:
1) By using an IR packet as in ROHC UDP, where the profile is
0x0004 and the static chain ends with the static part of an
IP header.
*********************************************************************
* Note: An open issue is how to terminate the static chain. Any *
* NextHdr/Protocol other than 4 (IPinIP) or 41 (IPv6) would *
* terminate the chain, but so would also a third IP header. *
*********************************************************************
At the compressor, IP SN is initialized to a random
value when the IR packet is sent.
2) By reusing an existing context where the existing static chain
contains the static part of an IP header.
*********************************************************************
* Note: This will have to be revised based on what is decided for *
* the above issue. *
*********************************************************************
As for ROHC UDP, this is done with an IR-DYN packet, identifying
profile 0x0004, where the dynamic chain corresponds to the prefix
of the existing static chain that ends with the IP header.
*********************************************************************
* Note: This will have to be revised based on what is decided for *
* the above issue. *
*********************************************************************
At the compressor, IP SN is initialized to a random value.
For ROHC IP, the dynamic part of a compressed packet is similar to
the one for ROHC UDP, with a two-octet field containing the SN added
to the end of the chain. This affects the format of dynamic chains in
IR and IR-DYN packets.
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4. Security Considerations
The security considerations of [RFC-3095] apply equally to this
document, without exceptions or additions.
5. IANA Considerations
ROHC profile identifier 0x0004 has been reserved by the IANA for the
profile defined in this document.
[TO BE REMOVED BEFORE PUBLICATION]
A ROHC profile identifier must be reserved by the IANA for the
profile defined in this document. Profile number 0x0004 has
previously been saved for this purpose, and should thus be used.
As for previous ROHC profiles, profile numbers 0xnnXX must also be
reserved for future updates of this profile. A suggested
registration in the "RObust Header Compression (ROHC) Profile
Identifiers" name space would then be:
0x0004 ROHC IP [RFCXXXX (this)]
0xnn04 Reserved
[END]
6. References
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC-3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima,
H., Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T.,
Le, K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro,
K., Wiebke, T., Yoshimura, T. and H. Zheng, "Robust
Header Compression (ROHC)", RFC 3095, July 2001.
[RFC-791] Postel, J., "Internet Protocol", RFC 791, September 1981.
[RFC-1883] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 1883, December 1995.
7. Author's Address
Lars-Erik Jonsson Tel: +46 920 20 21 07
Ericsson AB Fax: +46 920 20 20 99
Box 920
SE-971 28 Lulea
Sweden EMail: lars-erik.jonsson@ericsson.com
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This Internet-Draft expires April 28, 2003.
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