Network News Transfer Protocol (NNTP) Extension for Compression
draft-murchison-nntp-compress-01
The information below is for an old version of the document.
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| Author | Kenneth Murchison | ||
| Last updated | 2010-01-26 (Latest revision 2010-01-23) | ||
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draft-murchison-nntp-compress-01
Independent Submission K. Murchison
Internet-Draft Carnegie Mellon University
Intended status: Standards Track January 26, 2010
Expires: July 30, 2010
Network News Transfer Protocol (NNTP) Extension for Compression
draft-murchison-nntp-compress-01.txt
Abstract
This memo defines an extension to the Network News Transport Protocol
(NNTP) to allow a connection to be effectively and efficiently
compressed.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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This Internet-Draft will expire on July 30, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. The COMPRESS Extension . . . . . . . . . . . . . . . . . . . . 4
2.1. Advertising the COMPRESS Extension . . . . . . . . . . . . 4
2.2. COMPRESS Command . . . . . . . . . . . . . . . . . . . . . 4
2.2.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2.2. Description . . . . . . . . . . . . . . . . . . . . . 5
2.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 6
3. Compression Efficiency . . . . . . . . . . . . . . . . . . . . 9
4. Augmented BNF Syntax for the COMPRESS Extension . . . . . . . 11
4.1. Commands . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Capability entries . . . . . . . . . . . . . . . . . . . . 11
4.3. General Non-terminals . . . . . . . . . . . . . . . . . . 11
5. Summary of Response Codes . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. NNTP Compression Algorithm Registry . . . . . . . . . . . 14
7.1.1. Algorithm Name Registration Procedure . . . . . . . . 14
7.1.2. Comments on Algorithm Registrations . . . . . . . . . 15
7.1.3. Change Control . . . . . . . . . . . . . . . . . . . . 15
7.2. Registration of the DEFLATE Compression Algorithm . . . . 16
7.3. Registration of the NNTP COMPRESS Extension . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 20
Appendix B. Document History (to be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . . 21
B.1. Changes since -00 . . . . . . . . . . . . . . . . . . . . 21
Appendix C. Issues to be addressed . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
The goal of COMPRESS is to reduce the bandwidth usage of NNTP.
Compared to PPP compression [RFC1962] and modem-based compression
([MNP] and [V42bis]), COMPRESS offers greater compression efficiency.
COMPRESS can be used together with Transport Layer Security (TLS)
[RFC5246], Simple Authentication and Security Layer (SASL) encryption
[RFC4422], Virtual Private Networks (VPNs), etc.
Compared to TLS compression [RFC3749], NNTP COMPRESS has the
following advantages:
o COMPRESS can be implemented easily both by NNTP servers and
clients.
o COMPRESS benefits from an intimate knowledge of the NNTP
protocol's state machine, allowing for dynamic and aggressive
optimization of the underlying compression algorithm's parameters.
and the following disadvantages:
o When the TLS layer implements compression, any protocol using that
layer can transparently benefit from that compression (e.g., SMTP
and NNTP). COMPRESS is specific to NNTP.
In order to increase interoperability, it is desirable to have as few
different compression algorithms as possible, so this document
specifies only one. The DEFLATE algorithm (defined in [RFC1951]) is
standard, widely available and fairly efficient, and MUST be
implemented as part of this extension.
1.1. Conventions Used in This Document
The notational conventions used in this document are the same as
those in [RFC3977] and any term not defined in this document has the
same meaning as in that one.
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].
In the examples, commands from the client are indicated with [C], and
responses from the server are indicated with [S].
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2. The COMPRESS Extension
The COMPRESS extension is used to enable data compression on an NNTP
connection.
This extension provides a new COMPRESS command and has capability
label COMPRESS.
2.1. Advertising the COMPRESS Extension
A server supporting the COMPRESS command as defined in this document
will advertise the "COMPRESS" capability label in response to the
CAPABILITIES command ([RFC3977] Section 5.2). This capability MAY be
advertised both before and after any use of the MODE READER command
([RFC3977] Section 5.3), with the same semantics.
The COMPRESS capability label contains a whitespace-separated list of
available compression algorithms. This document defines one
compression algorithm: DEFLATE. This algorithm is mandatory to
implement and MUST be supported in order to advertise the COMPRESS
extension.
Future extensions may add additional compression algorithms to this
capability. Unrecognized algorithms MUST be ignored by the client.
Example:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] IHAVE
[S] COMPRESS DEFLATE X-SHRINK
[S] LIST ACTIVE NEWSGROUPS
[S] .
2.2. COMPRESS Command
2.2.1. Usage
This command MUST NOT be pipelined.
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Syntax
COMPRESS algorithm
Responses
291 Compression active
403 Unable to activate compression
502 Command unavailable [1]
[1] If a compression layer is already active, COMPRESS is not a valid
command (see Section 2.2.2).
Parameters
algorithm = Name of compression algorithm: "DEFLATE"
2.2.2. Description
The COMPRESS command instructs the server to use the named
compression algorithm ("DEFLATE" is the only one defined in this
document) for all commands and/or responses after COMPRESS.
The client MUST NOT send any further commands until it has seen the
result of COMPRESS.
If the requested compression algorithm is invalid (e.g., is not
supported), the server MUST reject the COMPRESS command with a 503
response ([RFC3977] Section 3.2.1). If the server is unable to
activate compression for any reason (e.g., a server configuration or
resource problem), the server MUST reject the COMPRESS command with a
403 response ([RFC3977] Section 3.2.1). Otherwise, the server issues
a 291 response and the compression layer takes effect for both client
and server immediately following the CRLF of the success reply.
Both the client and the server MUST know if there is a compression
layer active. A client MUST NOT attempt to activate compression (via
either the COMPRESS or STARTTLS [RFC4642] commands) if a compression
layer is already active. A server MUST NOT return the COMPRESS or
STARTTLS capability labels in response to a CAPABILITIES command
received after a compression layer is active, and a server MUST reply
with a 502 response code if a syntactically valid COMPRESS or
STARTTLS command is received while a compression layer is already
active.
For DEFLATE [RFC1951] (as for many other compression mechanisms), the
compressor can trade speed against quality. The decompressor MUST
automatically adjust to the parameters selected by the sender.
Consequently, the client and server are both free to pick the best
reasonable rate of compression for the data they send.
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When COMPRESS is combined with TLS [RFC5246] or SASL [RFC4422]
security layers, the processing order of the three layers MUST be
first COMPRESS, then SASL, and finally TLS. That is, before data is
transmitted it is first compressed. Second, if a SASL security layer
has been negotiated, the compressed data is then signed and/or
encrypted accordingly. Third, if a TLS security layer has been
negotiated, the data from the previous step is signed and/or
encrypted accordingly. When receiving data, the processing order
MUST be reversed. This ensures that before sending, data is
compressed before it is encrypted, independent of the order in which
the client issues the COMPRESS, AUTHINFO SASL [RFC4643], and STARTTLS
[RFC4642] commands.
2.2.3. Examples
Example of layering TLS and NNTP compression:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] STARTTLS
[S] AUTHINFO
[S] COMPRESS DEFLATE
[S] .
[C] STARTTLS
[S] 382 Continue with TLS negotiation
[TLS negotiation without compression occurs here]
[Following successful negotiation, all traffic is encrypted]
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] AUTHINFO USER
[S] COMPRESS DEFLATE
[S] .
[C] AUTHINFO USER fred
[S] 381 Enter passphrase
[C] AUTHINFO PASS flintstone
[S] 281 Authentication accepted
[C] COMPRESS DEFLATE
[S] 291 Compression active
[From this point on, all traffic is compresssed before being encrypted]
Example of a server failing to activate compression:
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[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] COMPRESS DEFLATE
[S] .
[C] COMPRESS DEFLATE
[S] 403 Unable to activate compression
Example of attempting to use an unsupported compression algorithm:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] COMPRESS DEFLATE
[S] .
[C] COMPRESS X-SHRINK
[S] 503 Compression algorithm not supported
Examples of a server refusing to compress twice:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] STARTTLS
[S] COMPRESS DEFLATE
[S] .
[C] STARTTLS
[S] 382 Continue with TLS negotiation
[TLS negotiation with compression occurs here]
[Following successful negotiation, all traffic is protected by TLS]
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] .
[C] COMPRESS DEFLATE
[S] 502 Compression already active via TLS
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[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] STARTTLS
[S] COMPRESS DEFLATE
[S] .
[C] COMPRESS DEFLATE
[S] 291 Compression active
[From this point on, all traffic is compresssed]
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] .
[C] STARTTLS
[S] 502 DEFLATE compression already active
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3. Compression Efficiency
This section is only informative.
NNTP poses some unusual problems for a compression layer.
Upstream traffic is fairly simple. Most NNTP clients send the same
few commands again and again, so any compression algorithm that can
exploit repetition works efficiently. The article posting and
transfer commands (e.g., POST, IHAVE, and TAKETHIS [RFC4644]) are an
exception; clients that send many article posting or transfer
commands may want to surround large multi-line data blocks with
flushes in the same way as is recommended for servers later in this
section.
Downstream traffic has the unusual property that several kinds of
data are sent, confusing all dictionary-based compression algorithms.
One type is NNTP simple responses and NNTP multi-line responses not
related to article header/body retrieval (e.g, CAPABILITIES, GROUP,
NEXT, STAT, DATE, NEWNEWS, LIST, OVER, CHECK [RFC4644], etc). These
are highly compressible; zlib using its least CPU-intensive setting
compresses typical responses to 25-40% of their original size.
Another type is article headers (as retrieved via the HEAD or ARTICLE
commands). These are equally compressible, and benefit from using
the same dictionary as the NNTP responses.
A third type is article body text (as retrieved via the BODY or
ARTICLE commands). Text is usually fairly short and includes much
ASCII, so the same compression dictionary will do a good job here,
too. When multiple messages in the same thread are read at the same
time, quoted lines, etc. can often be compressed almost to zero.
Finally, attachments (non-text article bodies retrieved via the BODY
and ARTICLE commands) are transmitted in encoded form, usually Base64
[RFC4648], UUencode [IEEE.1003-2.1992], or yEnc [yEnc].
When attachments are retrieved, DEFLATE may be able to compress them,
but the format of the attachment's encoding is usually not NNTP-like,
so the dictionary built while compressing NNTP does not help. The
compressor has to adapt its dictionary from NNTP to the attachment's
encoding format, and then back.
When attachments are retrieved in Base64 or UUencode form, these
encodings add another problem. 8-bit compression algorithms such as
DEFLATE work well on 8-bit file formats, however both Base64 and
UUencode transform a file into something resembling 6-bit bytes,
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hiding most of the 8-bit file format from the compressor.
When using the zlib library (see [RFC1951]), the functions
deflateInit2(), deflate(), inflateInit2(), and inflate() suffice to
implement this extension. The windowBits value must be in the range
-8 to -15, or else deflateInit2() uses the wrong format.
deflateParams() can be used to improve compression rate and resource
use. The Z_FULL_FLUSH argument to deflate() can be used to clear the
dictionary (the receiving peer does not need to do anything).
A server can improve downstream compression if it hints to the
compressor that the data type is about to change strongly, e.g., by
sending a Z_FULL_FLUSH at the start and end of large non-text multi-
line data blocks (before and after 'content-lines' in the definition
of 'multi-line-data-block' in [RFC3977] Section 9.8). Small multi-
line data blocks are best left alone. A possible boundary is 5kB.
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4. Augmented BNF Syntax for the COMPRESS Extension
This section describes the syntax of the COMPRESS extension using
ABNF [RFC5234]. It extends the syntax in Section 9 of [RFC3977], and
non-terminals not defined in this document are defined there. The
[RFC3977] ABNF should be imported first before attempting to validate
these rules.
4.1. Commands
This syntax extends the non-terminal "command", which represents an
NNTP command.
command =/ compress-command
compress-command = "COMPRESS" WS algorithm
4.2. Capability entries
This syntax extends the non-terminal "capability-entry", which
represents a capability that may be advertised by the server.
capability-entry =/ compress-capability
compress-capability = "COMPRESS" *(WS algorithm)
4.3. General Non-terminals
algorithm = "DEFLATE" / token
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5. Summary of Response Codes
This section contains a list of each new response code defined in
this document and indicates whether it is multi-line, which commands
can generate it, what arguments it has, and what its meaning is.
Response code 291
Generated by: COMPRESS
Meaning: Compression layer activated
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6. Security Considerations
As for TLS compression [RFC3749].
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7. IANA Considerations
7.1. NNTP Compression Algorithm Registry
The NNTP Compression Algorithm registry will be maintained by IANA.
The registry will be available at
<http://www.iana.org/assignments/nntp-compression-algorithms>.
The purpose of this registry is not only to ensure uniqueness of
values used to name NNTP compression algorithms, but also to provide
a definitive reference to technical specifications detailing each
NNTP compression algorithm available for use on the Internet.
There is no naming convention for NNTP compression algorithms; any
name that conforms to the syntax of a NNTP compression algorithm name
can be registered.
The procedure detailed in Section 7.1.1 is to be used for
registration of a value naming a specific individual mechanism.
Comments may be included in the registry as discussed in
Section 7.1.2 and may be changed as discussed in Section 7.1.3.
7.1.1. Algorithm Name Registration Procedure
IANA will register new NNTP compression algorithm names on a First
Come First Served basis, as defined in BCP 26 [RFC5226]. IANA has
the right to reject obviously bogus registration requests, but will
perform no review of claims made in the registration form.
Registration of an NNTP compression algorithm is requested by filling
in the following template:
Subject: Registration of NNTP compression algorithm X
NNTP compression algorithm name:
Security considerations:
Published specification (recommended):
Contact for further information:
Intended usage: (One of COMMON, LIMITED USE, or OBSOLETE)
Owner/Change controller:
Note: (Any other information that the author deems relevant may be
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added here.)
and sending it via electronic mail to IANA at <iana@iana.org>.
While this registration procedure does not require expert review,
authors of NNTP compression algorithms are encouraged to seek
community review and comment whenever that is feasible. Authors may
seek community review by posting a specification of their proposed
mechanism as an Internet-Draft. NNTP compression algorithms intended
for widespread use should be standardized through the normal IETF
process, when appropriate.
7.1.2. Comments on Algorithm Registrations
Comments on a registered NNTP compression algorithm should first be
sent to the "owner" of the algorithm and/or to the
<ietf-nntp@lists.eyrie.org> mailing list.
Submitters of comments may, after a reasonable attempt to contact the
owner, request IANA to attach their comment to the NNTP compression
algorithm registration itself by sending mail to <iana@iana.org>. At
IANA's sole discretion, IANA may attach the comment to the NNTP
compression algorithm's registration.
7.1.3. Change Control
Once an NNTP compression algorithm registration has been published by
IANA, the author may request a change to its definition. The change
request follows the same procedure as the registration request.
The owner of an NNTP compression algorithm may pass responsibility
for the algorithm to another person or agency by informing IANA; this
can be done without discussion or review.
The IESG may reassign responsibility for an NNTP compression
algorithm. The most common case of this will be to enable changes to
be made to algorithms where the author of the registration has died,
has moved out of contact, or is otherwise unable to make changes that
are important to the community.
NNTP compression algorithm registrations may not be deleted;
algorithms that are no longer believed appropriate for use can be
declared OBSOLETE by a change to their "intended usage" field; such
algorithms will be clearly marked in the lists published by IANA.
The IESG is considered to be the owner of all NNTP compression
algorithms that are on the IETF standards track.
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7.2. Registration of the DEFLATE Compression Algorithm
This section gives a formal definition of the DEFLATE compression
algorithm as required by Section 7.1.1 for the IANA registry.
NNTP compression algorithm name: DEFLATE
Security considerations: See Section 6 of this document
Published specification: This document
Contact for further information: Author of this document
Intended usage: COMMON
Owner/Change controller: IESG <iesg@ietf.org>.
Note: This algorithm is mandatory to implement
7.3. Registration of the NNTP COMPRESS Extension
This section gives a formal definition of the COMPRESS extension as
required by Section 3.3.3 of [RFC3977] for the IANA registry.
o The COMPRESS extension allows an NNTP connection to be effectively
and efficiently compressed.
o The capability label for this extension is "COMPRESS", whose
arguments list the available compression algorithms.
o This extension defines one new command, COMPRESS, whose behavior,
arguments, and responses are defined in Section 2.2.
o This extension does not associate any new responses with pre-
existing NNTP commands.
o This extension does affect the overall behavior of both server and
client, in that after successful use of the COMPRESS command, all
communication is transmitted in a compressed format.
o This extension does not affect the maximum length of commands or
initial response lines.
o This extension does not alter pipelining, but the COMPRESS command
cannot be pipelined
o Use of this extension does alter the capabilities list; once the
COMPRESS command has been used successfully, the COMPRESS
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capability can no longer be advertised by CAPABILITIES.
Additionally, the STARTTLS and MODE-READER capabilities MUST NOT
be advertised after successful execution of the COMPRESS command.
o This extension does not cause any pre-existing command to produce
a 401, 480, or 483 response.
o This extension is unaffected by any use of the MODE READER
command, however the MODE READER command MUST NOT be used in the
same session following a successful execution of the COMPRESS
command.
o The STARTTLS command MUST NOT be used in the same session
following a successful execution of the COMPRESS command.
o Published Specification: This document.
o Contact for Further Information: Author of this document.
o Change Controller: IESG <iesg@ietf.org>.
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8. References
8.1. Normative References
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)",
RFC 3977, October 2006.
[RFC4642] Murchison, K., Vinocur, J., and C. Newman, "Using
Transport Layer Security (TLS) with Network News Transfer
Protocol (NNTP)", RFC 4642, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
8.2. Informative References
[IEEE.1003-2.1992]
Institute of Electrical and Electronics Engineers,
"Information Technology - Portable Operating System
Interface (POSIX) - Part 2: Shell and Utilities (Vol. 1)",
IEEE Standard 1003.2, 1992.
[MNP] Held, G., "The Complete Modem Reference", Second
Edition, Wiley Professional Computing, May 1994.
[RFC1962] Rand, D. and K. Fox, "The PPP Compression Control Protocol
(CCP)", RFC 1962, June 1996.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4643] Vinocur, J. and K. Murchison, "Network News Transfer
Protocol (NNTP) Extension for Authentication", RFC 4643,
October 2006.
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[RFC4644] Vinocur, J. and K. Murchison, "Network News Transfer
Protocol (NNTP) Extension for Streaming Feeds", RFC 4644,
October 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC4978] Gulbrandsen, A., "The IMAP COMPRESS Extension", RFC 4978,
August 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[V42bis] International Telecommunications Union, "Data compression
procedures for data circuit-terminating equipment (DCE)
using error correction procedures", ITU-T Recommendation
V.42bis, January 1990.
[yEnc] Helbing, J., "yEnc - Efficient encoding for Usenet and
eMail", http://www.yenc.org.
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Appendix A. Acknowledgements
This document draws heavily on ideas in [RFC4978] by Arnt Gulbrandsen
and a large portion of this text was borrowed from that
specification.
Special acknowledgement also goes to Julien Elie and others who
commented privately on intermediate revisions of this document.
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Appendix B. Document History (to be removed by RFC Editor before
publication)
B.1. Changes since -00
o Made DEFLATE the mandatory to implement compression algorithm.
o Removed the requirement that clients/servers implementing COMPRESS
also implement TLS compression.
o Added an example of a client trying to use an unsupported
compression algorithm.
o Rewrote Compression Efficiency (Section 3) as follows:
* Included a sample listing of which NNTP commands produce which
type of data to be compressed.
* Removed discussion of attachments in binary form and
incompressible file formats.
* Mentioned UUencode and yEnc encoding of attachments.
o Added IANA registry of NNTP compression algorithms.
o Miscellaneous editorial changes submitted by Julien Elie.
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Appendix C. Issues to be addressed
o What 2xx code should we use when compression is activated? 20x,
28x, 29x?
o Should we restrict the ABNF for compression algorithms?
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Author's Address
Kenneth Murchison
Carnegie Mellon University
5000 Forbes Avenue
Cyert Hall 285
Pittsburgh, PA 15213
US
Phone: +1 412 268 2638
Email: murch@andrew.cmu.edu
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