<COMPRESSION> February 2006
Lemonade
Internet Draft: LZIP S. H. Maes
Document: draft-ietf-lemonade-compress-00 R. Cromwell
(Editors)
Expires: August 2006 February 2006
COMPRESSION
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Lemonade investigates adding mobile optimizations for the next
version of the Lemonade Profile. LZIP addresses this task and
provides an extension to allow compression of the exchanged text and
binary literals, typically message body parts.
Conventions used in this document
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In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
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 [RFC2119].
An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocol(s) it
implements. An implementation that satisfies all the MUST or REQUIRED
level and all the SHOULD level requirements for a protocol is said to
be "unconditionally compliant" to that protocol; one that satisfies
all the MUST level requirements but not all the SHOULD level
requirements is said to be "conditionally compliant." When
describing the general syntax, some definitions are omitted as they
are defined in [RFC3501].
Table of Contents
Status of this Memo ........................................ 1
Copyright Notice............................................ 1
Abstract.................................................... 1
Conventions used in this document........................... 1
Table of Contents........................................... 2
1. Introduction............................................. 2
2. The CAPABILITY Command................................... 3
3. LZIP Commands............................................ 3
4. LZIP Response............................................ 3
5. Formal Syntax............................................ 4
Security Considerations..................................... 4
References.................................................. 4
Future Work................................................. 5
Version History............................................. 5
Acknowledgments............................................. 5
Authors Addresses........................................... 6
Intellectual Property Statement............................. 6
Disclaimer of Validity...................................... 7
Copyright Statement ........................................ 7
1.
Introduction
LZIP provides an extension to allow compression of text and binary
literals.
While it could be argued that transport could provide generic
compression of the data (e.g. TLS with NULL Cipher), application
level compression presents the advantage to be better tunable to the
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type of data being requested, for example, to avoid compression of
already compressed data.
Compression performances depend on the actual types of e-mail that
are received. They change between text bodies and different types of
attachments. In general, LZIP presents a worthwhile gain over
uncompressed or network compressed only approached at very little
extra cost for the implementer.
Bandwidth optimization are important features required in particular
to support mobile email use cases [MEMAIL][OMA-ME-RD]
2.
The CAPABILITY Command
Servers which support LZIP MUST return ‘LZIP’ in the response list to
a capability command.
Example: A LEMONADE server that implements LZIP.
C: a001 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=LOGIN IDLE LZIP
S: a001 OK CAPABILITY completed
3.
LZIP Commands
The LZIP command is an extension of [RFC3516] IMAP BINARY, which
introduces three new commands “LZIP”, “LZIP.PEEK”, “LZIP.SIZE” that
parallel the syntax and semantics of “BINARY”, “BINARY.PEEK”, and
“BINARY.SIZE” in [RFC3516]. In general, LZIP inherits all of the
requirements and semantics of [RFC3516]’s “BINARY” and “BINARY.PEEK”,
except that the content transfer encoding being requested is
understood to be the result of what would be returned from BINARY
decoding, followed by the application of the DEFLATE algorithm.
Example: Zipping a body part fetch
C: A1 FETCH 123 LZIP.PEEK[1.2]
S: * LZIP[1.2]~{1234}
S: ….binary decoded and deflated data….
S: A1 OK FETCH completed
As mentioned in RFC3516, LZIP.SIZE is a potentially expensive
operation, as in LZIP, so clients should be aware that making
successive requests for the same part may be expensive.
4.
LZIP Response
As the result of processing an LZIP command, two new responses, LZIP
and LZIP.SIZE which parallel that responses of [RFC3516] are
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introduced. They are identical in syntax and semantics of the BINARY
responses in [RFC3516] in everyway, except that the resulting binary
literal is understood to be in DEFLATE format.
5.
Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation. Elements not defined here can be found in
the formal syntax of the [ABNF], [RFC3501], and [ABNFEXTEND].
The create ABNF grammar in [RFC3501] is hereby modified to the
grammar defined in [ABNFEXTEND]
fetch-att =/ "LZIP" [".PEEK"] section-binary [partial]
/ "LZIP.SIZE" section-binary
msg-att-static =/ "LZIP" section-binary SP (nstring / literal8)
/ "LZIP.SIZE" section-binary SP number
Security Considerations
LZIP does not introduce additional security consideration with
respect to IMAPv4Rev1.
References
[LEMONADEPROFILE] Maes, S.H. and Melnikov A., "Lemonade Profile",
draft-ietf-lemonade-profile-XX.txt, (work in progress).
[MEMAIL] Maes, S.H., “Lemonade and Mobile e-mail", draft-maes-
lemonade-mobile-email-xx.txt, (work in progress).
[OMA-ME-RD] Open Mobile Alliance Mobile Email Requirement Document,
(Work in progress). http://www.openmobilealliance.org/
[P-IMAP] Maes, S.H., Lima R., Kuang, C., Cromwell, R., Ha, V. and
Chiu, E., Day, J., Ahad R., Jeong W-H., Rosell G., Sini, J., Sohn
S-M., Xiaohui F. and Lijun Z., "Push Extensions to the IMAP
Protocol (P-IMAP)", draft-maes-lemonade-p-imap-xx.txt, (work in
progress).
[RFC1951] Deutsch, P. “DEFLATE Compressed Data Format Specification
version 1.3”, RFC1951, May 1996.
http://www.ietf.org/rfc/rfc1951
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[RFC2119] Brader, S. "Keywords for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
http://www.ietf.org/rfc/rfc2119
[RFC3501] Crispin, M. "IMAP4, Internet Message Access Protocol
Version 4 rev1", RFC 3501, March 2003.
http://www.ietf.org/rfc/rfc3501
[RFC3516] Nerenberg, L. “IMAP4 Binary Content Extension”, RFC3516,
April 2003.
http://www.ietf.org/rfc/rfc3516
Future Work
Should a new “compressed literal” be considered paralleling the
binary literal8 syntax? For example, %~{nz-number}? Potential
applications could be its usage in APPEND/CATENATE.
Version History
Release 00 of draft-maes-lemonadel-lzip
Initial release published in June 2005
Release 01 of draft-maes-lemonadel-lzip
Shortened list of editors. Authors pushed to acknowledgements
Section 2: Addition of exact compression algorithm
references
Section 4:
Addition of exact compression algorithm references
Considerations on command compression added
Correction and updates of examples
References:
Additional references on compression algorithms and IMAP4
Binary.
Release 02 of draft-maes-lemonadel-lzip
Reworked to model IMAP BINARY
Release 00 of IETF draft
Re-cast LZIP to focus on compression of text and binary
literals.
Acknowledgments
The authors want to thank all who have contributed key insight and
extensively reviewed and discussed the concepts of LPSEARCH and its
early introduction P-IMAP [P-IMAP]. In particular, this includes the
authors of the P-IMAP draft: Rafiul Ahad – Oracle Corporation, Eugene
Chiu – Oracle Corporation, Ray Cromwell – Oracle Corporation, Jia-der
Day – Oracle Corporation, Vi Ha – Oracle Corporation, Wook-Hyun Jeong
– Samsung Electronics Co. LTF, Chang Kuang – Oracle Corporation,
Rodrigo Lima – Oracle Corporation, Stephane H. Maes – Oracle
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Corporation, Gustaf Rosell - Sony Ericsson, Jean Sini – Symbol
Technologies, Sung-Mu Son – LG Electronics, Fan Xiaohui - CHINA
MOBILE COMMUNICATIONS CORPORATION (CMCC), Zhao Lijun - CHINA MOBILE
COMMUNICATIONS CORPORATION (CMCC). We also want to give a special
thanks to A. Melnikov for his review and suggestions.
Authors Addresses
Stephane H. Maes
Oracle Corporation
500 Oracle Parkway
M/S 4op634
Redwood Shores, CA 94065
USA
Phone: +1-650-607-6296
Email: stephane.maes@oracle.com
Ray Cromwell
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Anil Srivastava
Sun Microsystems
4150 Network Circle SCA15/201
Santa Clara, CA 94065
anil.srivastava@sun.com
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