Network Working Group X. Fu
Internet-Draft C. Dickmann
Intended status: Experimental University of Goettingen
Expires: October 30, 2010 J. Crowcroft
University of Cambridge
April 28, 2010
General Internet Signaling Transport (GIST) over Stream Control
Transmission Protocol (SCTP) and Datagram Transport Layer Security
(DTLS)
draft-ietf-nsis-ntlp-sctp-11.txt
Abstract
The General Internet Signaling Transport (GIST) protocol currently
uses TCP or Transport Layer Security (TLS) over TCP for connection
mode operation. This document describes the usage of GIST over the
Stream Control Transmission Protocol (SCTP) and Datagram Transport
Layer Security (DTLS). The use of SCTP can take advantage of
features provided by SCTP, namely streaming-based transport, support
of multiple streams to avoid head of line blocking, the support of
multi-homing to provide network level fault tolerance, as well as
partial reliability extension for partially reliable data
transmission. This document also specifies how to establish GIST
security over datagram transport protocols using an extension to
DTLS.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 30, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
Fu, et al. Expires October 30, 2010 [Page 1]
Internet-Draft GIST over SCTP and DTLS April 2010
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
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 Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 4
3. GIST Over SCTP . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Message Association Setup . . . . . . . . . . . . . . . . 4
3.1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.2. Protocol-Definition: Forwards-SCTP . . . . . . . . . . 4
3.2. Effect on GIST State Maintenance . . . . . . . . . . . . . 5
3.3. PR-SCTP Support . . . . . . . . . . . . . . . . . . . . . 5
3.4. API between GIST and NSLP . . . . . . . . . . . . . . . . 6
4. Bit-Level Formats . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MA-Protocol-Options . . . . . . . . . . . . . . . . . . . 6
5. Application of GIST over SCTP . . . . . . . . . . . . . . . . 7
5.1. Multi-homing support of SCTP . . . . . . . . . . . . . . . 7
5.2. Streaming support in SCTP . . . . . . . . . . . . . . . . 7
6. NAT Traversal Issue . . . . . . . . . . . . . . . . . . . . . 8
7. Use of DTLS with GIST . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Fu, et al. Expires October 30, 2010 [Page 2]
Internet-Draft GIST over SCTP and DTLS April 2010
1. Introduction
This document describes the usage of the General Internet Signaling
Transport (GIST) protocol [1] and Datagram Transport Layer Security
(DTLS) 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) [7] for signaling message transport. However, some
Next Steps in Signaling (NSIS) Signaling Layer Protocol (NSLP) [8]
context information has a definite lifetime, therefore, the GIST
transport protocol could benefit from flexible retransmission, so
stale NSLP messages that are held up by congestion can be dropped.
Together with the head-of-line blocking and multihoming 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. Like TCP, SCTP supports
reliability, congestion control and 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. Furthermore, SCTP offers an advantage of
message-oriented transport instead of using the byte stream oriented
TCP where one has to provide its own framing mechanisms. In
addition, its Partial Reliability extension (PR-SCTP) [3] supports
partial retransmission based on a programmable retransmission timer.
Furthermore, Datagram Transport Layer Security (DTLS) [4] provides a
viable solution for securing SCTP [5], which allows SCTP to use
almost all its transport features and its extensions.
This document defines the use of SCTP as a transport protocol and the
use of DTLS as a security mechanism for GIST Messaging Associations
and discusses the implications on GIST state maintenance and API
between GIST and NSLPs. Furthermore, this document describes how
GIST should be interfaced to SCTP and used by NSLPs in order to
exploit the additional capabilities offered by SCTP to deliver GIST
C-mode messages more effectively. More specifically:
o How to use the multiple streams feature of SCTP.
o How to use the PR-SCTP extension of SCTP.
o How to take advantage of the multi-homing support of SCTP.
The methods of using an unchanged SCTP with GIST described in this
document do not require any changes to the high level operation and
structure of GIST. Addition of new transport options requires
additional interface code and configuration support to allow
applications to exploit the additional transport when appropriate.
In addition, SCTP over GIST implementations MUST support the optional
feature of fragmentation of SCTP user messages.
Fu, et al. Expires October 30, 2010 [Page 3]
Internet-Draft GIST over SCTP and DTLS April 2010
Additionally, this document also specifies how to establish GIST
security using DTLS for use in combination with e.g., SCTP and UDP.
2. Terminology and Abbreviations
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 [6]. Other
terminologies and abbreviations used in this document are taken from
related specifications (e.g., [1] and [2]).
3. GIST Over SCTP
This section defines a new MA-Protocol-ID type, "Forwards-SCTP", for
using SCTP as GIST transport protocol.
3.1. Message Association Setup
3.1.1. Overview
The basic GIST protocol specification defines two possible protocols
to be used in Messaging Associations, namely Forwards-TCP and TLS.
This information are main part of the Stack Configuration Data (SCD)
[1]. This document adds Forwards-SCTP and DTLS as another two
possible protocol options. In Forwards-SCTP, analog to Forwards-TCP,
connections between peers are opened in the forwards direction, from
the querying node, towards the responder.
3.1.2. Protocol-Definition: Forwards-SCTP
This MA-Protocol-ID "Forwards-SCTP" denotes a basic use of SCTP
between peers. Support for this protocol is OPTIONAL. If this
protocol is offered, MA-protocol-options data MUST also be carried in
the SCD object. The MA-protocol-options field formats are:
o in a Query: no information apart from the field header.
o in a Response: 2 byte port number at which the connection will be
accepted, followed by 2 pad bytes.
The connection is opened in the forwards direction, from the querying
node towards the responder. The querying node MAY use any source
address and source port. The destination for establishing the
message association MUST be derived from information in the Response:
the address from the interface- address from the Network-Layer-
Information object and the port from the SCD object as described
above.
Fu, et al. Expires October 30, 2010 [Page 4]
Internet-Draft GIST over SCTP and DTLS April 2010
Associations using Forwards-SCTP can carry messages with the transfer
attribute Reliable=True. If an error occurs on the SCTP connection
such as a reset, as can be reported by an SCTP socket API
notification[9], GIST MUST report this to NSLPs as discussed in
Section 4.1.2 of [1]. For the multi-homing scenario, when a
destination address of a GIST over SCTP peer encounters a change, the
SCTP API will notify GIST about the availability of different SCTP
endpoint addresses and possible change of the primary path.
3.2. Effect on GIST State Maintenance
As SCTP provides additional functionality over TCP, this section
discusses the implications of using GIST over SCTP on GIST State
Maintenance.
While SCTP defines uni-directional streams, for the purpose of this
document, the concept of a bi-directional stream is used.
Implementations MUST establish downstream and upstream (uni-
directional) SCTP streams always together and use the same stream
identifier in both directions. Thus, the two uni-directional streams
(in opposite directions) form a bi-directional stream.
Due to the multi-streaming support of SCTP, it is possible to use
different SCTP streams for different resources (e.g., different NSLP
sessions), 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). However, there are limitations to the use of multi-
streaming. All GIST messages for a particular session MUST be sent
over the same SCTP stream to assure the NSLP assumption of in-order
delivery. Multiple sessions MAY share the same SCTP stream based on
local policy.
The GIST concept of Messaging Association re-use is not affected by
this document or the use of SCTP. All rules defined in the GIST
specification remain valid in the context of GIST over SCTP.
3.3. PR-SCTP Support
A variant of SCTP, PR-SCTP [3] provides a "timed reliability"
service, which would be particular useful for delivering GIST
Connection mode messages. 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
partially 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 using "timed reliability"
Fu, et al. Expires October 30, 2010 [Page 5]
Internet-Draft GIST over SCTP and DTLS April 2010
service instead of a standard SCTP association, if available, to
support more flexible transport features for potential needs of
different NSLPs.
In a standard SCTP, instead, if a node has sent the first
transmission before the lifetime expires, then the message MUST be
sent as a normal reliable message. During episodes of congestion
this is particularly unfortunate, as retransmission wastes bandwidth
that could have been used for other (non-lifetime expired) messages.
The "timed reliability" service in PR-SCTP eliminates this issue and
is hence RECOMMENDED to be used for GIST over PR-SCTP.
3.4. 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,
that need special consideration when used in the context of SCTP.
The relevant primitives from [1] are as follows:
o The Timeout parameter in API "SendMessage": According to [1], this
parameter represents the "length of time GIST should attempt to
send this message before indicating an error." When used with PR-
SCTP, this parameter is used as the timeout for the "timed
reliability" service of PR-SCTP.
o "NetworkNotification": According to [1], this primitive "is passed
from GIST to a signalling application. It indicates that a
network event of possible interest to the signalling application
occurred." Here, if SCTP detects a failure of the primary path,
GIST SHOULD also indicate this event to the NSLP by calling this
primitive with Network-Notification-Type "Routing Status Change".
This notification should be done even if SCTP was able to retain
an open connection to the peer due to its multi-homing
capabilities.
4. Bit-Level Formats
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.
Fu, et al. Expires October 30, 2010 [Page 6]
Internet-Draft GIST over SCTP and DTLS April 2010
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: SCTP port number | Reserved :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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. Application of GIST over SCTP
5.1. Multi-homing support of SCTP
In general, the multi-homing support of SCTP can be used to improve
fault-tolerance in case of a path- or link-failure. Thus, GIST over
SCTP would be able to deliver NSLP messages between peers even if the
primary path is not working anymore. However, for the Message
Routing Methods (MRMs) defined in the basic GIST specification such a
feature is only of limited use. The default MRM is path-coupled,
which means, that if the primary path is failing for the SCTP
association, it most likely is also for the IP traffic that is
signaled for. Thus, GIST would need to perform a refresh to the NSIS
nodes to the alternative path anyway to cope with the route change.
When the two endpoints of a multi-homed SCTP association (but none of
the intermediate nodes between them) support NSIS, GIST over SCTP
provides a robust means for GIST to deliver NSLP messages even when
the primary path fails but at least one alternative path between
these (NSIS-enabled) endpoints of the multihomed path is available.
Additionally, the use of the multi-homing support of SCTP provides
GIST and the NSLP with another source to detect route changes.
Furthermore, for the time between detection of the route change and
recovering from it, the alternative path offered by SCTP can be used
by the NSLP to make the transition more smoothly. Finally, future
MRMs might have different properties and therefore benefit from
multi-homing more broadly.
5.2. Streaming support in SCTP
Streaming support in SCTP is advantageous for GIST. It allows better
parallel processing, in particular by avoiding head of line blocking
issue in TCP. Since a same GIST MA may be reused by multiple
sessions, using TCP as transport for GIST signaling messages
belonging to different sessions may be blocked if another message is
dropped. In the case of SCTP, this can be avoided as different
Fu, et al. Expires October 30, 2010 [Page 7]
Internet-Draft GIST over SCTP and DTLS April 2010
sessions having different requirements can belong to different
streams, thus a message loss or reordering in a stream will only
affect the delivery of messages within that particular stream, and
not any other streams.
6. NAT Traversal Issue
NAT traversal for GIST over SCTP will follow Section 7.2 of [1] and
the GIST extensibility capabilities defined in [10]. This
specification does not define NAT traversal procedure for GIST over
SCTP, although an approach for SCTP NAT traversal is described in
[11].
7. Use of DTLS with GIST
This section specifies a new "MA-Protocol-ID" for the use of DTLS in
GIST, which denotes a basic use of datagram transport layer channel
security, initially in conjunction with SCTP over GIST. It provides
authentication, integrity and optionally replay protection for
control packets. The use of DTLS for securing GIST over SCTP allows
GIST to take the advantage of features provided by SCTP and its
extensions. Note replay protection is not available for DTLS over
SCTP [5]. The usage of DTLS for GIST over SCTP is similar to TLS for
GIST as specified in [1], where a stack-proposal containing both MA-
Protocol-IDs for SCTP and DTLS during the GIST handshake phase.
GIST message associations using DTLS may carry messages with transfer
attributes requesting confidentiality or integrity protection. The
specific DTLS version will be negotiated within the DTLS layer
itself, but implementations MUST NOT negotiate to protocol versions
prior to DTLS v1.0 and MUST use the highest protocol version
supported by both peers. GIST nodes supporting DTLS MUST be able to
negotiate the DTLS NULL and block ciphers and SHOULD be able to
negotiate the new cipher suites. They MAY negotiate any mutually
acceptable ciphersuite that provides authentication, integrity, and
confidentiality. The same rules for negotiating TLS cipher suites as
specified in Section 5.7.3 of [1] apply.
No MA-protocol-options field is required for DTLS. The configuration
information for the transport protocol over which DTLS is running
(e.g. SCTP port number) is provided by the MA-protocol-options for
that protocol.
Fu, et al. Expires October 30, 2010 [Page 8]
Internet-Draft GIST over SCTP and DTLS April 2010
8. Security Considerations
The security considerations of [1], [2] and [4] apply. Following
[5], replay detection of DTLS over SCTP is not supported.
The usage of DTLS [4] for securing GIST over datagram transport
protocols MUST be implemented and SHOULD be used. An implementation
of GIST over SCTP with no PR-SCTP support MAY use TLS for its channel
security, when DTLS is not available between two GIST peers.
9. IANA Considerations
This specification requests the following codepoints (MA-Protocol-
IDs) be assigned in a registry created by [1]:
+---------------------+------------------------------------------+
| MA-Protocol-ID | Protocol |
+---------------------+------------------------------------------+
| 3 | SCTP opened in the forwards direction |
| | |
| 4 | DTLS initiated in the forwards direction |
+---------------------+------------------------------------------+
Note that MA-Protocol-ID 4 is never used alone but always coupled
with a transport protocol in the stack proposal.
10. Acknowledgments
The authors would like to thank John Loughney, Jukka Manner, Magnus
Westerlund, Robert Hancock, Andrew McDonald, Martin Stiemerling,
Fang-Chun Kuo, Jan Demter, Lauri Liuhto, Michael Tuexen, and Roland
Bless for their helpful suggestions.
11. References
11.1. Normative References
[1] Schulzrinne, H. and M. Stiemerling, "GIST: General Internet
Signalling Transport", draft-ietf-nsis-ntlp-20 (work in
progress), June 2009.
[2] Stewart, R., "Stream Control Transmission Protocol", RFC 4960,
September 2007.
Fu, et al. Expires October 30, 2010 [Page 9]
Internet-Draft GIST over SCTP and DTLS April 2010
[3] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad,
"Stream Control Transmission Protocol (SCTP) Partial
Reliability Extension", RFC 3758, May 2004.
[4] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[5] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control Transmission
Protocol (SCTP)", draft-ietf-tsvwg-dtls-for-sctp-05 (work in
progress), March 2010.
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
[7] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[8] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080,
June 2005.
[9] Stewart, R., Poon, K., Tuexen, M., Yasevich, V., and P. Lei,
"Sockets API Extensions for Stream Control Transmission
Protocol (SCTP)", draft-ietf-tsvwg-sctpsocket-22 (work in
progress), March 2010.
[10] Manner, J., Bless, R., Loughney, J., and E. Davies, "Using and
Extending the NSIS Protocol Family", draft-ietf-nsis-ext-07
(work in progress), April 2010.
[11] Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
Transmission Protocol (SCTP) Network Address Translation",
draft-ietf-behave-sctpnat-02 (work in progress), December 2009.
Fu, et al. Expires October 30, 2010 [Page 10]
Internet-Draft GIST over SCTP and DTLS April 2010
Authors' Addresses
Xiaoming Fu
University of Goettingen
Institute of Computer Science
Goldschmidtstr. 7
Goettingen 37077
Germany
Email: fu@cs.uni-goettingen.de
Christian Dickmann
University of Goettingen
Institute of Computer Science
Goldschmidtstr. 7
Goettingen 37077
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
Fu, et al. Expires October 30, 2010 [Page 11]