Movatterモバイル変換

Network Working Group                                       R. PereiraRequest for Comments: 2394                        TimeStep CorporationCategory: Informational                                  December 1998IP Payload Compression Using DEFLATEStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   This document describes a compression method based on the DEFLATE   compression algorithm.  This document defines the application of the   DEFLATE algorithm to the IP Payload Compression Protocol.Table of Contents1. Introduction...................................................21.1 The DEFLATE Compression Algorithm...........................21.2 Licensing...................................................21.3 Specification of Requirements...............................32. DEFLATE Algorithm Implementation...............................32.1 Compression.................................................32.2 Decompression...............................................43. Thresholds.....................................................44. IPSec Transform Identifier.....................................45. Security Considerations........................................46. References.....................................................57. Acknowledgments................................................58. Editor's Address...............................................59. Full Copyright Statement.......................................6Pereira                      Informational                      [Page 1]

RFC 2394          IP Payload Compression Using DEFLATE     December 19981. Introduction   The IP Payload Compression Protocol allows the compression of IP   datagrams by supporting different compression algorithms.  This   document describes how to integrate the DEFLATE compression algorithm   [Deutsch96] into IPCOMP [IPCOMP].   This document SHOULD be read in conjunction with [IPCOMP] and MUST be   taken in its context.1.1 The DEFLATE Compression Algorithm   The 'deflate' compression format [Deutsch96], as used by the PKZIP   and gzip compressors and as embodied in the freely and widely   distributed zlib [Gailly95] library source code, has the following   features:   o an apparently unencumbered encoding and compression algorithm,     with an open and publicly-available specification.   o low-overhead escape mechanism for incompressible data.  The PPP     Deflate specification offers options to reduce that overhead     further.   o heavily used for many years in networks, on modem and other point-     to-point links to transfer files for personal computers and     workstations.   o easily achieves 2:1 compression on the Calgary corpus [Corpus90]     using less than 64KBytes of memory on both sender and receive.1.2 Licensing   The zlib source is widely and freely available, subject to the   following copyright:      (C) 1995 Jean-Loup Gailly and Mark Adler      This software is provided 'as-is', without any express or implied      warranty.  In no event will the authors be held liable for any      damages arising from the use of this software.      Permission is granted to anyone to use this software for any      purpose, including commercial applications, and to alter it and      redistribute it freely, subject to the following restrictions:Pereira                      Informational                      [Page 2]

RFC 2394          IP Payload Compression Using DEFLATE     December 1998      1. The origin of this software must not be misrepresented; you         must not claim that you wrote the original software. If you use         this software in a product, an acknowledgment in the product         documentation would be appreciated but is not required.      2. Altered source versions must be plainly marked as such, and         must not be misrepresented as being the original software.   3. This notice may not be removed or altered from any source         distribution.         Jean-Loup Gailly        Mark Adler         gzip@prep.ai.mit.edu    madler@alumni.caltech.edu      If you use the zlib library in a product, we would appreciate      *not* receiving lengthy legal documents to sign. The sources are      provided for free but without warranty of any kind.  The library      has been entirely written by Jean-Loup Gailly and Mark Adler; it      does not include third-party code.   The deflate format and compression algorithm are based on Lempel-Ziv   LZ77 compression; extensive research has been done by the GNU Project   and the Portable Network Graphics working group supporting its patent   free status.1.3 Specification of Requirements   The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",   and "MAY" that appear in this document are to be interpreted as   described in [Bradner97].2. DEFLATE Algorithm Implementation   The DEFLATE compression algorithm was designed by Phil Katz and its   details are publicly available in [Deutsch96].  Thus it is a good   freely available algorithm to implement within IPCOMP.   Compression and decompression algorithm details should be followed as   outlined in [Deutsch96] or the use of a software library may be   preferable.  Since IPComp is a stateless protocol, history MUST be   cleared between packets when either compressing or decompressing.2.1 Compression   As defined in [IPCOMP], the compression process is determined by the   IP Compression Association (IPCA).  The IPCA MUST define the DEFLATE   algorithm for the process within this document to take place.Pereira                      Informational                      [Page 3]

RFC 2394          IP Payload Compression Using DEFLATE     December 1998   The compression process entails compressing the data from the IP   datagram and placing the result after the IPComp header.  For   example, compressing a TCP datagram;   Before:  IP TCP ...   After:   IP IPCOMP (TCP ...)   Please note how everything after the IPCOMP header is compressed.   DEFLATE allows for a number of compression levels ranging from best   compression but slow to fast compression.  The level that one   compresses data is implementation dependant since it is always   compatible with the decompression algorithm.2.2 Decompression   As in the compression process, the IPCA defines the parameters and   algorithm to utilize for the decompression process.   As defined in [IPCOMP] the data after the IPComp header is   decompressed and replaces the IPComp header within the IP header.   Decompression using the DEFLATE algorithm follows the decompression   process defined in [Deutsch96].3. Thresholds   As stated in [IPCOMP], compression on small buffers does not usually   work as well as on fast links since the time it takes to compress is   slower than the time to transport the data.  Informal tests show that   the average buffer size that produces larger results is around 90   bytes.  Thus implementations SHOULD NOT attempt to compress buffers   smaller than 90 bytes.   Other than a packet size limit, no compressibility test as defined in   [IPCOMP] is outlined in this document.4. IPSec Transform Identifier   [IPDOI] states that the ISAKMP IPCOMP transform ID for the DEFLATE   compression algorithm is IPCOMP_DEFLATE.  No other ISAKMP parameters   are required for the IPCOMP DEFLATE algorithm.5. Security Considerations   This document does not add any further security considerations that   [IPCOMP] and [Deutsch96] have already declared.Pereira                      Informational                      [Page 4]

RFC 2394          IP Payload Compression Using DEFLATE     December 19986. References   [IPCOMP]    Shacham, A., Monsour, R., Pereira, R., and M. Thomas, "IP               Payload Compression Protocol (IPComp)",RFC 2393,               December 1998.   [Deutsch96] Deutsch, P., "DEFLATE Compressed Data Format               Specification version 1.3",RFC 1951, May 1996.   [IPDOI]     Piper, D., "The Internet IP Security Domain of               Interpretation for ISAKMP",RFC 2407, November 1998.   [Corpus90]  Bell, T.C., Cleary, G. G. and Witten, I.H., "Text               Compression", Prentice_Hall, Englewood Cliffs NJ, 1990.               The compression corpus itself can be found inftp://ftp.uu.net/pub/archiving/zip/   [Gailly95]  Gailly, J.-L., "Zlib 0.95 beta"7. Acknowledgments   The author wishes to thank all of the active members of the IPPCP   working group especially Abraham Shacham and Naganand Doraswamy.8. Editor's Address   Roy Pereira   TimeStep Corporation   Phone: +1 (613) 599-3610 x 4808   EMail: rpereira@timestep.com   The IP Payload Compression Protocol (IPPCP) working group can be   contacted via email (ippcp@cisco.com) or through its chair:   Naganand Dorswamy   Bay Networks   EMail: naganand@baynetworks.comPereira                      Informational                      [Page 5]

RFC 2394          IP Payload Compression Using DEFLATE     December 19989.  Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Pereira                      Informational                      [Page 6]