Internet DRAFT - draft-maes-lemonade-lzip
draft-maes-lemonade-lzip
<LZIP> September 2005
Lemonade
Internet Draft: LZIP S. H. Maes
Document: draft-maes-lemonade-lzip-02 R. Cromwell
(Editors)
Expires: March 2006 September 2005
LZIP
Status of this Memo
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Abstract
Push Extensions to the IMAP protocol (P-IMAP) defines extensions to
the IMAPv4 Rev1 protocol [RFC3501] for optimization in a mobile
setting, aimed at delivering extended functionality for mobile
devices with limited resources. LZIP provides an extension to allow
compression of the exchanged messages to and from the mobile client.
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
Abstract..........................................................1
Conventions used in this document.................................1
Table of Contents.................................................2
1. Introduction...................................................2
2. Relation with other specifications.............................3
3. The CAPABILITY Command.........................................3
4. LZIP Command...................................................4
Security Considerations...........................................5
References........................................................6
Future Work.......................................................6
Version History...................................................6
Acknowledgments...................................................7
Authors Addresses.................................................7
Intellectual Property Statement...................................9
Full Copyright Statement..........................................9
1. Introduction
The Push-IMAP protocol (P-IMAP) is based on IMAPv4 Rev1 [RFC3501],
but contains additional enhancements for optimization in a mobile
setting. LZIP provides an extension to allow compression of the
exchanged messages to and from the mobile client.
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
type of data.
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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 present a significant gain over
uncompressed or network compressed only approached at very little
extra cost for the implementer.
LZIP allows for compression of responses to a command. Practical
testing results shows significant performance improvement when the
responses to FETCH FLAGS or header information, body parts and
attachments are compressed.
Bandwidth optimization are are important features required in
particular to support mobile email use cases [MEMAIL][OMA-ME-RD]
2. Relation with other specifications
LZIP can be seen as an command that allows optimization of IMAP for
mobile clients.
The Lemonade Profile [LEMONADEPROFILE] specifies the Lemonade Pull
Model that governs the exchanges among mail servers or between
desktop mail client and mail servers. Lemonade investigates adding
mobile optimizations for the next version of the profile.
LZIP should be seen as a way to address the issues of bandwidth
optimization and an input to the Lemonade Profile work.
This document assumes that clients MUST be compliant to LZIP, if they
decide to use LZIP. The server that advertises support for LZIP via
CAPABILITY MUST be compliant to LZIP for its exchanges with the
mobile client.
LZIP adopts the æliteral8Æ format of the IMAP BINARY specification
[RFC3516] for its response.
LZIP relies on the DEFLATE compression algorithm and format specified
in [RFC1951].
3. The CAPABILITY Command
The CAPABILITY command is defined in RFC3501, section 6.1.1. The
client sends a CAPABILITY command so it can query the server to find
out what commands it supports. In RFC3501, the IMAP server is
allowed to specify additional capabilities not included in that
specification. A server that supports LZIP conforms to that
requirement, and must list that it supports LZIP.
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A server can also enumerate individually the other commands that it
supports.
capability_cmd = tag SP "CAPABILITY"
Valid States: NOT AUTHENTICATED, AUTHENTICATED, SELECTED, or LOGOUT
Responses: REQUIRED untagged response: CAPABILITY
Result: OK - capability completed
BAD - command unknown or arguments invalid
Example: A P-IMAP server that implements LZIP.
C: a001 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=LOGIN IDLE LZIP
S: a001 OK CAPABILITY completed
4. LZIP Command
The LZIP command is used for zipping the response (and optionally the
request) of a command and can be used while the server is in any
state. In either case, the data is compressed according to [RFC1951]
and transmitted according to the æliteral8Æ rule of [RFC3516]. The
LZIP command takes in a complete second command (including a tag for
that command). In an untagged response to LZIP, the server gives a
æliteral8Æ response including the number of bytes in the zipped
response to the enclosed command, as well as the response to that
command in ZIP format.
LZIP can also compress the command request, although this is most
useful when the command request is large. Short command strings may
still benefit from compression, but most likely, the overhead of the
LZIP syntax itself, which adds about 20 characters to the command
request, will wipe out any gains.
The format for LZIP is
lzip_cmd = tag SP "LZIP" SP [INLINE æ{æ length æ}Æ] (command or
zipped-compressed command)
Valid States: NOT AUTHENTICATED, AUTHENTICATED, SELECTED, or LOGOUT
Responses: "{" num "}" zipped-response-to-command
Result: OK - the command given was g-zipped correctly and sent
BAD - invalid arguments, i.e. command given is in the wrong
format.
Example: Zipping the response to a FETCH command.
C: A001 LZIP A002 FETCH 1:* ALL
S: * LZIP ~{10933843723}
S: ...[zipped response to FETCH command]... CRLF
S: A001 OK LZIP completed
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When the client unzips the body of the response to the FETCH command
it gets:
* 1 FETCH ...
...
A002 OK FETCH completed
Example: command request compression using FETCH
C: A001 LZIP INLINE {1234} (zip-compressed string æa002 FETCH ...Æ)
S: * LZIP ~{4567}
S: ... [zipped response to FETCH command] . . .CRLF
S: A001 OK LZIP completed
The client can then unzip the body of the response as above.
Because the server will not know the size of the compressed response
until after it has compressed the stream, and in order to enable the
server to reduce the amount of resources it must dedicate to handling
each request, a server is permitted to break up the zipped stream
into blocks and return multiple LZIP responses for a single request.
Example: zipping the response of a large message fetch
C: A001 LZIP A002 FETCH 1 RFC822
S: * LZIP ~{821}
S: à CRLF
S: * LZIP ~{954}
S: à CRLF
S: * LZIP ~{987}
S: à CRLF
S: * LZIP ~{123}
S: à CRLF
S: A001 OK LZIP Completed
In this case, the server broke up the 3500 byte response into chunks
of size 1024 bytes of less, compressed them, and the results of the 4
compressed blocks were of length 821, 954, 987, and 123. The server
MUST return the LZIP dictionary/compression state between blocks.
The client MUST uncompress the blocks and concatenate them in the
order sent from the server.
Security Considerations
LZIP does not introduce additional security consideration with
respect to IMAPv4Rev1.
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References
[LEMONADEPROFILE] Maes, S.H. and Melnikov A., "Lemonade Profile",
draft-ietf-lemonade-profile-XX.txt, (work in progress).
[MEMAIL] Maes, S.H., ôLemonade 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. ôDEFLATE Compressed Data Format Specification
version 1.3ö, RFC1951, May 1996.
http://www.ietf.org/rfc/rfc1951
[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. ôIMAP4 Binary Content Extensionö, RFC3516,
April 2003.
http://www.ietf.org/rfc/rfc3516
Future Work
TBD
Version History
Release 00
Initial release published in June 2005
Release 01
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
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References:
Additional references on compression algorithms and IMAP4
Binary.
Release 03
Added support for block encryption.
Acknowledgments
The authors want to thank all who have contributed key insight and
extensively reviewed and discussed the concepts of LDELIVER and its
early introduction as XDELIVER in P-IMAP [P-IMAP].
The following contributed to the authoring of LZIP.
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
Rafiul Ahad
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Eugene Chiu
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Ray Cromwell
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Jia-der Day
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
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USA
Wook-Hyun Jeong
Samsung Electronics,CO., LTD
416, Maetan-3dong, Yeongtong-gu,
Suwon-city, Gyeonggi-do,
Korea 442-600
Tel: +82-31-279-8289
E-mail: wh75.jeong@samsung.com
Chang Kuang
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Rodrigo Lima
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
USA
Gustaf Rosell
Sony Ericsson
P.O. Box 64
SE-164 94 Kista,
Sweden
Tel: +46 8 508 780 00
Jean Sini
6480 Via Del Oro
San Jose, CA 95119
USA
Sung-Mu Son
LG Electronics
Mobile Communication Technology Research Lab.
Tel: +82-31-450-1910
E-Mail: sungmus@lge.com
Fan Xiaohui
Product Development Division
R&D CENTER
CHINA MOBILE COMMUNICATIONS CORPORATION (CMCC)
ADD: 53A, Xibianmennei Ave.,Xuanwu District,
Beijing,100053
China
TEL:+86 10 66006688 EXT 3137
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Zhao Lijun
CMCC R&D
ADD: 53A, Xibianmennei Ave.,Xuanwu District,
Beijing,100053
China
TEL:.8610.66006688.3041
Dwayne Bennett
Consilient
P.O. Box 2172
St. John's, NL A1C 6E6
Canada
Tel: +1 709 576 1706
E-mail: bennett@consilient.com
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Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
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except as set forth therein, the authors retain all their rights.
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