Internet DRAFT - draft-ahmed-tsvwg-sctpdsum
draft-ahmed-tsvwg-sctpdsum
H. Ahmed
S. Boffa
Category: Internet Draft Motorola Inc.
August 15 2001
SCTP Dynamic Checksum selection
draft-ahmed-tsvwg-sctpdsum-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
When SCTP was initially accepted as RFC2960 the Adler-32 checksum
was specified to be used. However, inlight of issues raised in
[STONE] it has been proposed that a more robust algorithm such as
[CRC-32] be used instead. This poses compatibility problems for
existing implementations of SCTP that are already using
the Adler-32 algorithm for computing checksums. This document
proposes a dynamic method to preserve backward compatibility
between the two checksum algorithms.
Table of Contents
1. Introduction................................................1
1.1 Conventions..............................................2
2. Checksum algorithm selection................................2
2.1 Basic operation...........................................2
3. Acknowledgments.............................................3
4. Authors' Addresses..........................................3
5. References..................................................3
5.1 Normative References......................................3
5.2 Informative References....................................3
1. Introduction
RFC2960 specified the Adler-32 checksum algorithm as its checksum
algorithm. Since then, observations from [STONE] have shown the
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Internet Draft SCTP Dynamic Checksum Selection August 2001
CRC-32 algorithm to be a more robust choice. The use of one
(or the other) algorithm will effectively prevent two different
implementations from communicating with each other. As there are
already implementations using the Adler-32 checksum this document
proposes that both versions of the checksum be supported. The
decision on which algorithm is to be used should be done dynamically
at the initialization of an association.
This change will provide the following benefits (in no particular
order):
[a] Backward compatibility between the newer and older
implementations.
[b] Negligible performance penalty based on algorithm selection
since it is only done once at the initialization stage of an
association.
[c] Requires no change to the existing data flows for the SCTP
protocol.
1.1 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
[RFC2119].
2. Checksum algorithm selection
Checksum computation (at the the Transport layer) has been
traditionally defined by the protocol specification such as RFC2960
for SCTP. Since changing the checksum algorithm effectively makes two
implementations of SCTP incompatible with each other the following
algorithm is designed to make this selection dynamic.
2.1 Basic Operation
Upon receiving an INIT packet from a peer, the host SHALL first apply
the CRC-32 algorithm to validate the received datagram. If the CRC-32
algorithm fails, then the Adler-32 checksum algorithm will be
applied. If the Adler-32 checksum fails then the packet is discarded
in compliance with [RFC2960] section 6.8.
However, if the datagram passes Adler-32 checksum then the host shall
mark the peer as running the Adler-32 checksum. The host (if it
chooses to continue on with the association) will respond using the
Adler-32 checksum algorithm. Note, that this checksum setting is
applicable to all SCTP interactions between the host and the peer.
Further, the host may refuse the association request if it does not
wish to support the Adler-32 variant of the checksum. In this case
the packet may be silently discarded. It is also recommended that
future SCTP implementations adhere to the more robust CRC-32
checksum algorithm and the choice of supporting the Adler-32 variant
be left as an implementation choice.
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3. Acknowledgments
The authors would like to thank the following people that have
provided comments and input on the checksum issue:
Stephen G. Boffa
4. Authors' Addresses
Haseeb Ahmed
Motorola Inc.
CDMA Systems Division
8201 E McDowell Rd
Scottsdale, AZ 85257
USA
EMail: hahmed1@email.mot.com
5. References
5.1 Normative References
[CRC-32] ITU-T Recommendation V.41, "Code-independent
error-control system," November 1989.
5.2 Informative References
[STONE] Doctoral Thesis
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Ahmed et.al. [Page 4]
