Network Working Group X. Fu
Internet-Draft C. Dickmann
Expires: August 24, 2006 University of Goettingen
J. Crowcroft
University of Cambridge
February 20, 2006
General Internet Signaling Transport (GIST) over SCTP
draft-fu-nsis-ntlp-sctp-01.txt
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Abstract
The General Internet Signaling Transport (GIST) protocol currently
uses TCP or TLS over TCP for connection mode operation. This
document describes the usage of GIST over the Stream Control
Transmission Protocol (SCTP). The use of SCTP can take the advantage
of features provided by SCTP, namely streaming-based transport,
support of multiple streams to avoid head of line blocking, and the
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support of multi-homing to provide network level fault tolerance.
Additionally, the support for some extensions of SCTP is also
discussed, namely its Partial Reliability Extension and the usage of
TLS over SCTP.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
3. GIST Over SCTP . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Message Association Setup . . . . . . . . . . . . . . . . 4
3.2. Stack-Configuration-Data information for SCTP . . . . . . 4
3.3. Effect on GIST State Maintenance . . . . . . . . . . . . . 5
3.4. PR-SCTP Support . . . . . . . . . . . . . . . . . . . . . 5
3.5. API between GIST and NSLP . . . . . . . . . . . . . . . . 5
3.5.1. SendMessage . . . . . . . . . . . . . . . . . . . . . 6
3.5.2. NetworkNotification . . . . . . . . . . . . . . . . . 6
3.6. TLS over SCTP Support . . . . . . . . . . . . . . . . . . 6
4. Bit-Level Formats . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MA-Protocol-Options . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
This document describes the usage of the General Internet Signaling
Transport (GIST) protocol [1] over the Stream Control Transmission
Protocol (SCTP) [2].
GIST, in its initial specification for connection mode operation,
runs on top of a byte-stream oriented transport protocol providing a
reliable, in-sequence delivery, i.e., using the Transmission Control
Protocol (TCP) [4] for signaling message transport. However, some
NSLP context information has a definite lifetime, therefore, the GIST
transport protocol must accommodate flexible retransmission, so stale
NSLP messages that are held up by congestion can be dropped.
Together with the head-of-line blocking issue and other issues with
TCP, these considerations argue that implementations of GIST should
support the Stream Control Transport Protocol (SCTP)[2] as an
optional transport protocol for GIST, especially if deployment over
the public Internet is contemplated. Like TCP, SCTP supports
reliability, congestion control, fragmentation. Unlike TCP, SCTP
provides a number of functions that are desirable for signaling
transport, such as multiple streams and multiple IP addresses for
path failure recovery. In addition, its Partial Reliability
extension (PR-SCTP) [5] supports partial retransmission based on a
programmable retransmission timer.
This document shows how GIST should be used with SCTP to provide
these additional features to deliver the GIST C-mode messages (which
can in turn carry NSIS Signaling Layer Protocol (NSLP) [6] messages
as payload). More specifically:
how to use the multiple streams feature of SCTP.
how to handle the message oriented nature of SCTP.
how to take the advantage of multi-homing support of SCTP.
Additionally, this document also discusses how to support two
extensions of SCTP, namely PR-SCTP [5] and TLS over SCTP [7].
The method described in this document does not require any changes of
GIST or SCTP. It is only required that SCTP implementations support
the optional feature of fragmentation of SCTP user messages.
2. Terminology and Abbreviations
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL", in this document are to be interpreted as described in
BCP 14, RFC 2119 [3]. Other terminologies and abbreviations used in
this document are taken from related specifications (e.g., [1] and
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[2]) as follows:
o TLS - Transport Layer Security
o SCTP - Stream Control Transmission Protocol
o PR-SCTP - SCTP Partial Reliability Extension
o MRM - Message Routing Method
o MRI - Message Routing Information
o MRS - Message Routing State
o MA - A GIST Messaging Association is a single connection between
two explicitly identified GIST adjacent peers on the data path. A
messaging association may use a specific transport protocol and
known ports. If security protection is required, it may use a
specific network layer security association, or use a transport
layer security association internally. A messaging association is
bidirectional; signaling messages can be sent over it in either
direction, and can refer to flows of either direction.
o SCTP Association - A protocol relationship between SCTP endpoints,
composed of the two SCTP endpoints and protocol state information.
An association can be uniquely identified by the transport
addresses used by the endpoints in the association. Two SCTP
endpoints MUST NOT have more than one SCTP association between
them at any given time.
o Stream - A sequence of user messages that are to be delivered to
the upper-layer protocol in order with respect to other messages
within the same stream.
3. GIST Over SCTP
3.1. Message Association Setup
The basic GIST protocol specification defines two possible protocols
to be used in message associations, namely Forwards-TCP and TLS.
This document adds Forwards-SCTP as another possible protocol. In
Forwards-SCTP, analog to Forwards-TCP, connections between peers are
opened in the forwards direction, from the querying node, towards the
responder. SCTP connections may carry NSLP messages with the
transfer attribute 'reliable'.
A new MA-Protocol-ID type, "Forwards-SCTP", is defined in this
document for using SCTP as GIST transport protocol.
3.2. Stack-Configuration-Data information for SCTP
In order to run GIST over SCTP, the Stack-Proposal and Stack-
Configuration-Data objects need to recognize the Forwards-SCTP MA-
Protocol-ID type, and interpret it for the transport protocol
negotiation during the GIST MA setup handshake (e.g., whether SCTP
runs alone or together with TLS).
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In turn, the "MA-protocol-options" field for Forwards-SCTP needs to
be defined for the Stack-Configuration-Data object defined of GIST.
This "MA-protocol-options" contains proposed values for the initial
and maximum retransmission timeout (RTO) as well as a port number in
the case of Response messages. The proposed values for RTO are only
suggestions to the peer and may be overridden by local policy. In
fact, in order to avoid denial of service attacks, the minimum RTO
value is not included in the proposal and in addition implementations
should only accept reasonable RTO proposals.
The MA-protocol-options formats are:
o in a Query: 4 byte RTO initial value and 4 byte RTO maximum value
o in a Response: 4 byte RTO initial value, 4 byte RTO maximum value
and 2 byte port number at which the connection will be accepted.
3.3. Effect on GIST State Maintenance
A GIST MA is established over an SCTP association, which comprises
one or more SCTP streams. Each of such streams can be used for one
or multiple NSLP sessions (i.e., one or more MRSs). After completing
a GIST MA setup, which implicitly establishes a bi-directional SCTP
stream, C-mode messages can be sent over the SCTP association in
either direction. Due to multi-streaming support of SCTP, it is easy
to maintain sequencing of messages that affect the same resource
(e.g., the same NSLP session), rather than maintaining all messages
along the same transport connection/association in a correlated
fashion as TCP (which imposes strict (re)ordering and reliability per
transport level).
3.4. PR-SCTP Support
A variant of SCTP, PR-SCTP [5] provides a "timed reliability"
service. It allows the user to specify, on a per message basis, the
rules governing how persistent the transport service should be in
attempting to send the message to the receiver. Because of the chunk
bundling function of SCTP, reliable and partial reliable messages can
be multiplexed over a single PR-SCTP association. Therefore, a GIST
over SCTP implementation SHOULD attempt to establish a PR-SCTP
association instead of a standard SCTP association, if available, to
support more flexible transport features for potential needs of
different NSLPs.
3.5. API between GIST and NSLP
GIST specification defines an abstract API between GIST and NSLPs.
While this document does not change the API itself, the semantics of
some parameters have slightly different interpretation in the context
of SCTP. This section only lists those primitives and parameters,
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that need special consideration when used in the context of SCTP.
The relevant primitives are repeatet from [1] to improve readability,
but [1] remains authoritative.
3.5.1. SendMessage
The SendMessage primitive is used by the NSLP to initiate sending of
messages.
SendMessage ( NSLP-Data, NSLP-Data-Size, NSLP-Message-Handle,
NSLP-Id, Session-ID, MRI,
SSI-Handle, Transfer-Attributes, Timeout, IP-TTL, GHC )
The following parameter has changed semantics:
Timeout: According to [1] this parameter represents the "length of
time GIST should attempt to send this message before indicating an
error". When used with SCTP, this parameter is also used as the
timeout for the "timed reliability" service of PR-SCTP.
3.5.2. NetworkNotification
The NetworkNotification primitive is passed from GIST to an NSLP. It
indicates that a network event of possible interest to the NSLP
occurred.
NetworkNotification ( MRI, Network-Notification-Type )
If SCTP detects a failure of the primary path, GIST should indicate
this event to the NSLP by calling the NetworkNotification primitive
with Network-Notification-Type "Routing Status Change". This
notification should be done even if SCTP was able to remain an open
connection to the next peer due to its multi-homing capabilities.
3.6. TLS over SCTP Support
GIST using TLS over SCTP is similar to GIST using TLS over TCP ([1],
Section 5.7.3). One should note that an SCTP association with TLS
support takes advantages of SCTP, such as multi-streaming and multi-
homing.
A future version of this document will add more text on this topic.
4. Bit-Level Formats
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4.1. MA-Protocol-Options
This section provides the bit-level format for the MA-protocol-
options field that is used for SCTP protocol in the Stack-
Configuration-Data object of GIST (see Section 3.2).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial RTO value | Maximum RTO value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: SCTP port number | Reserved :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Initial RTO value = Initial RTO value (SCTP configuration) in msec
Maximum RTO value = Maximum RTO value (SCTP configuration) in msec
SCTP port number = Port number at which the responder will accept
SCTP connections
The SCTP port number is only supplied if sent by the responder.
5. Security Considerations
The security considerations of both [1] and [2] apply. Further
security analysis is needed to consider any additional security
vulnerabilities, and will be included in an updated draft.
6. IANA Considerations
A new MA-Protocol-ID (Forwards-SCTP) needs to be assigned, with a
recommended value of 3.
7. Acknowledgments
The authors would like to thank John Loughney and Jan Demter for
their helpful suggestions.
8. References
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8.1. Normative References
[1] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signaling Transport", draft-ietf-nsis-ntlp-09 (work in
progress), February 2006.
[2] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[4] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[5] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad,
"Stream Control Transmission Protocol (SCTP) Partial Reliability
Extension", RFC 3758, May 2004.
[6] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080,
June 2005.
[7] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer
Security over Stream Control Transmission Protocol", RFC 3436,
December 2002.
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Authors' Addresses
Xiaoming Fu
University of Goettingen
Institute for Informatics
Lotzestr. 16-18
Goettingen 37083
Germany
Email: fu@cs.uni-goettingen.de
Christian Dickmann
University of Goettingen
Institute for Informatics
Lotzestr. 16-18
Goettingen 37083
Germany
Email: mail@christian-dickmann.de
Jon Crowcroft
University of Cambridge
Computer Laboratory
William Gates Building
15 JJ Thomson Avenue
Cambridge CB3 0FD
UK
Email: jon.crowcroft@cl.cam.ac.uk
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