Network Working Group R. Moskowitz
Internet-Draft S. Hares
Intended status: Standards Track Huawei
Expires: December 29, 2017 I. Faynberg
Stargazers Consulting, LLC
H. Lu
Retired
P. Giacomin
FreeLance
June 27, 2017
GPCOMP
draft-moskowitz-gpcomp-02.txt
Abstract
This document describes a protocol intended to provide lossless
compression for use within any datagram. It is particularly intended
for use in encrypted datagrams where lower-level compression is
ineffective.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Compression Process . . . . . . . . . . . . . . . . . . . . . 3
3.1. Compressed Payload . . . . . . . . . . . . . . . . . . . 3
3.2. Uncompressing Conundrum . . . . . . . . . . . . . . . . . 4
3.3. Non-Expansion Policy . . . . . . . . . . . . . . . . . . 4
4. Compressed Datagram Structure . . . . . . . . . . . . . . . . 5
4.1. Implied Structure . . . . . . . . . . . . . . . . . . . . 5
4.2. GPComp header for Explicit Structure . . . . . . . . . . 5
5. Negotiating GPComp . . . . . . . . . . . . . . . . . . . . . 5
5.1. The GPCA . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Using IKEv2 . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Using HIP . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Generic payload compression is a protocol to reduce the size of most
datagrams. This protocol will increase the overall communication
performance by compressing the datagrams, provided the participating
devices have sufficient computation power, through either CPU
capacity or a compression coprocessor, and the communication is over
constrained links.
Generic payload compression is especially useful when encryption is
applied to datagrams. Encrypting a datagram causes the data to be
random in nature, rendering compression at lower protocol layers
ineffective.
This document defines the Generic payload compression protocol
(GPComp), a GPComp packet structure, the GPComp Association (GPCA),
and several methods to negotiate the GPCA.
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Other documents shall specify how a specific compression algorithm
can be used with the Generic payload compression protocol. Such
algorithms are beyond the scope of this document.
This document draws heavily on IPCOMP [RFC3173].
2. Terms and Definitions
2.1. Requirements 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 [RFC2119].
2.2. Definitions
GPCA: The Generic Payload Compression Protocol Association. This is
the collection of attributes and values that define how GPComp
operates.
3. Compression Process
The compression processing has two phases: compressing of outbound
datagrams ("compression") and decompressing of inbound datagrams
("decompression"). The compression processing MUST be lossless,
ensuring that the datagram, after being compressed and decompressed,
is identical to the original datagram.
Each datagram is compressed and decompressed by itself without any
relation to other datagrams ("stateless compression"), as datagrams
may arrive out of order or not arrive at all.
Processing of inbound datagrams MUST support both compressed and non-
compressed datagrams, in order to meet the non-expansion policy
requirements, as defined in Section 3.3.
3.1. Compressed Payload
Compression is applied to a single datagram. The size of a
compressed payload, generated by the compression algorithm, MUST be
in whole octet units.
As compression is optional for each datagram associated within the
GPCA, an identification mechanism is REQUIRED for each datagram.
Minimally this can be a single option bit within the datagram's
header (if it has one). Alternatively, the GPComp header, defined in
Section 4.2, is inserted immediately preceding the compressed
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payload. The receiving side MUST be able to distinguish between
compressed and uncompressed payloads.
3.2. Uncompressing Conundrum
The receiver MUST be able to recognize the condition of no
compression for the case where there is no datagram header option
flag for compression and only the presense of the GPComp header
indicates a compressed payload. In this case, the payload itself has
no indication that GPComp is enabled for the payload, but there is
nothing to decompress. The receiving process has to be able to
identify the payload as lacking the GPComp header and act
appropriately. Thus it is best if there is a datagram header
compression flag (for example in SSE [I-D.moskowitz-sse]) and the
GPComp header is not even used.
3.3. Non-Expansion Policy
If the total size of a compressed payload and the GPComp header (if
present) is not smaller than the size of the original payload, the
datagram MUST be sent in the original non-compressed form. To
clarify: If an datagram is sent non-compressed, no GPComp header is
added to the datagram. This policy ensures saving the decompression
processing cycles and avoiding incurring datagram fragmentation if
the expanded datagram is larger than the MTU. It does present a
potential conundrum Section 3.2 to the receiver.
Small datagrams are likely to expand as a result of compression.
Therefore, a numeric threshold should be applied before compression,
where datagrams of size smaller than the threshold are sent in the
original form without attempting compression. The numeric threshold
is implementation dependent.
A datagram payload with compressed content tends not to compress any
further. The previously compressed payload may be the result of
external processes, such as compression applied by an upper layer in
the communication stack, or by an off-line compression utility. An
adaptive algorithm should be implemented to avoid the performance
hit. For example, if the compression of i consecutive IP datagrams
of an GPCA fails, the next several datagrams, say k, are sent without
attempting compression. If then the next j datagrams also fail to
compress, a larger number of datagrams, say k+n, are sent without
attempting compression. Once a datagram is compressed successfully,
the normal process of IPComp restarts. Such an adaptive algorithm,
including all the related thresholds, is implementation dependent.
During the processing of the payload, the compression algorithm MAY
periodically apply a test to determine the compressibility of the
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processed data, similar to the requirements of [V42BIS]. The nature
of the test is algorithm dependent. Once the compression algorithm
detects that the data is non-compressible, the algorithm SHOULD stop
processing the data, and the payload is sent in the original non-
compressed form.
4. Compressed Datagram Structure
The compressed datagram structure for GPComp can be implied or
explicit. The implied structure is used with datagrams that have a
header field with option flags and a length field or end-of-datagram
identifier. The explicit structure uses the GPComp header.
4.1. Implied Structure
The implied structure takes one option flag bit in the datagram
header. This bit is ONE if that datagram is compressed or ZERO if
not compressed. The compression algorithm is specified within the
GPCA. The implied structure can be used within SSE.
4.2. GPComp header for Explicit Structure
The GPComp header is used for datagrams that do not have a defined
header with an options field, or do not have an available bit in the
header to flag compression status. IPFIX [RFC7011] and NETCONF
[RFC6536] use such a datagram.
The GPComp header is identical to the IPComp header [RFC3173]. This
is for done for simplicity sake. Although it is possible to design a
GPComp header of only 2 bytes, this would break the typical 32 bit
word alignment in Internet Protocol headers. In many uses, the Next
Header field will be NULL; this is set by the GPCA.
5. Negotiating GPComp
The use of GPComp and its options (e.g. compression algorithm) should
be part of the communication start up process. Although GPComp can
be manually set up, this may result in a lack of agility in
compression algorithm selection. That is, only one algorithm is used
and cannot easily be changed. Thus manual set up for GPComp should
be limited to testing needs.
An application may use any internal set up mechanism for negotiating
GPComp. However, as compression is frequently used in conjunction
with encryption, the application may call a Key Management Protocol
(KMP) and request that the KMP set up GPComp.
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5.1. The GPCA
The GPCA is a data structure that controls the operation of GPComp.
The content of the GPCA is application dependent but it will always
include the Compression Parameter Index (CPI) as defined in IPCOMP.
5.2. Using IKEv2
At set up, and application may call IKEv2 [RFC7296]. This may be to
enable ESP in Transport Mode [RFC4303] or SSE for secure
communications. It the same time, IKE may be instructed to negotiate
IPCOMP, but the application will use the negotiated IPCOMP CPI for
GPComp.
5.3. Using HIP
At set up, and application may call HIPv2 [RFC7401] or HIP-DEX
[I-D.ietf-hip-dex]. This may be to enable ESP in BEET Mode [RFC7402]
or SSE for secure communications.
HIP does not currently include a negotiation for compression. A
GPCOMP_INFO parameter is proposed in [I-D.moskowitz-ssls-hip]. It is
unclear at this time if this could also be used for IPCOMP, or if a
separate parameter is needed for it.
6. IANA Considerations
In [I-D.moskowitz-ssls-hip], IANA is requested to assign a HIP
parameter value for the Compression Transform.
7. Security Considerations
TBD
8. Contributors
TBD
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC3173] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP
Payload Compression Protocol (IPComp)", RFC 3173,
DOI 10.17487/RFC3173, September 2001,
<http://www.rfc-editor.org/info/rfc3173>.
9.2. Informative References
[I-D.ietf-hip-dex]
Moskowitz, R. and R. Hummen, "HIP Diet EXchange (DEX)",
draft-ietf-hip-dex-05 (work in progress), February 2017.
[I-D.moskowitz-sse]
Moskowitz, R., Faynberg, I., Lu, H., Hares, S., and P.
Giacomin, "Session Security Envelope", draft-moskowitz-
sse-04 (work in progress), October 2016.
[I-D.moskowitz-ssls-hip]
Moskowitz, R., Xia, L., Faynberg, I., Hares, S., and P.
Giacomin, "Secure Session Layer Services KMP via HIP",
draft-moskowitz-ssls-hip-01 (work in progress), October
2016.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012,
<http://www.rfc-editor.org/info/rfc6536>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<http://www.rfc-editor.org/info/rfc7011>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<http://www.rfc-editor.org/info/rfc7401>.
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[RFC7402] Jokela, P., Moskowitz, R., and J. Melen, "Using the
Encapsulating Security Payload (ESP) Transport Format with
the Host Identity Protocol (HIP)", RFC 7402,
DOI 10.17487/RFC7402, April 2015,
<http://www.rfc-editor.org/info/rfc7402>.
[V42BIS] CCITT, "Data Compression Procedures for Data Circuit
Terminating Equipment (DCE) Using Error Correction
Procedures", Recommendation V.42 bis, January 1990.
Authors' Addresses
Robert Moskowitz
Huawei
Oak Park, MI 48237
Email: rgm@labs.htt-consult.com
Susan Hares
Huawei
7453 Hickory Hill
Saline, MI 48176
USA
Email: shares@ndzh.com
Igor Faynberg
Stargazers Consulting, LLC
East Brunswick, NJ 08816
USA
Email: igorfaynberg@gmail.com
Huilan Lu
Retired
Email: huilanlu2@gmail.com
Pierpaolo Giacomin
FreeLance
Email: yrz@anche.no
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