Network Working Group X. Fu Internet-Draft C. Dickmann Expires: April 19, 2006 University of Goettingen J. Crowcroft University of Cambridge October 16, 2005 General Internet Signaling Transport (GIST) over SCTP draft-fu-nsis-ntlp-sctp-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 19, 2006. Copyright Notice Copyright (C) The Internet Society (2005). 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 Fu, et al. Expires April 19, 2006 [Page 1] Internet-Draft GIST over SCTP October 2005 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. Stack-Configuration-Data information for SCTP . . . . . . . 4 3.2. Changes to GIST State Maintenance . . . . . . . . . . . . . 5 3.3. Multi-homing Consideration . . . . . . . . . . . . . . . . 5 3.4. PR-SCTP Support . . . . . . . . . . . . . . . . . . . . . . 5 3.4.1. Changes to API between GIST and NSLP . . . . . . . . . 6 3.5. TLS over SCTP Support . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Fu, et al. Expires April 19, 2006 [Page 2] Internet-Draft GIST over SCTP October 2005 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 Fu, et al. Expires April 19, 2006 [Page 3] Internet-Draft GIST over SCTP October 2005 [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. Stack-Configuration-Data information for SCTP A new MA-Protocol-ID type, "SCTP", is defined in this document for using SCTP as GIST transport protocol. In order to run GIST over SCTP, the Stack-Proposal and Stack- Configuration-Data objects need to recognize the 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). As an example, assuming SCTP MA-Protocol-ID type is 3, TLS is 2 and TCP is 1, then Stack-Proposal for different transport will be: SCTP only: 3 TLS over SCTP: 3, 2 TCP only: 1 TLS over TCP: 1, 2 An SCTP association is opened in the downstreaming direction, i.e., from the querying node towards the responder node. In order to establish an association, a port needs to be negotiated. Therefore, Fu, et al. Expires April 19, 2006 [Page 4] Internet-Draft GIST over SCTP October 2005 a Higher-Layer-Addressing format for the GIST Stack-Configuration- Data object needs to be defined. The content of Higher-Layer- Addressing depends on the node type: o Querying node: No information (only padding) o Responding node: 2-byte port number at which the connection will be accepted TBD: The number of streams may also be part of it and negotiated between a GIST Querying node and Responding node. 3.2. Changes to 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 the all messages along the same transport connection/association in a correlated fashion as TCP (which imposes strict (re)ordering and reliability per transport level). It is up to local policy when to create a new stream within an SCTP association. 3.3. Multi-homing Consideration Multi-homing support is an important feature of SCTP and potentially provides a better path failure recovery for GIST transport. However, this feature requires appropriate interpretation (even re-adjustment) of the keying information for both MA and MRI tables. For instance, if the communicating end hosts have multiple IP addresses and use them for signaling, usually the primary IP addresses will be used for creating and maintaining corresponding MRS. This will also involve how to reuse MA table. It may be beneficial if additional MRM and state keying methods for multi-homed signaling scenarios. A future version of this document will add more text on this aspect. 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 unreliable messages can be multiplexed over a single PR-SCTP association. Therefore, a GIST Fu, et al. Expires April 19, 2006 [Page 5] Internet-Draft GIST over SCTP October 2005 over SCTP implementation SHOULD attempt to establish a PR-SCTP association instead of a standardq SCTP association, if available, to support more flexible transport features for potential needs of different NSLPs. Concerning the use of PR-SCTP in GIST, at least the following change to the API between GIST and NSLP needs to be considered. 3.4.1. Changes to API between GIST and NSLP In the GIST-NSLP API SendMessage() primitive, the current values of the Transfer-Attribute "Reliability" can be either 'unreliable' or 'reliable' as specified in [1]. When PR-SCTP is used, some distinction from standard SCTP needs to be introduced. The SendMessage() primitive already contains a Timeout value, which specifies how long GIST should attempt to send a message before indicating an error. In the case of PR-SCTP this value should be used as the timer value for the "timed reliablity". If no "timed reliability" is available, the Timeout parameter should have no impact on SCTP. 3.5. 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. 4. 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. 5. IANA Considerations A new MA-Protocol-ID (SCTP) needs to be assigned, with a recommended value of 3. 6. Acknowledgments The authors would like to thank John Loughney and Jan Demter for their helpful suggestions. 7. References Fu, et al. Expires April 19, 2006 [Page 6] Internet-Draft GIST over SCTP October 2005 7.1. Normative References [1] Schulzrinne, H. and R. Hancock, "GIST: General Internet Signaling Transport", draft-ietf-nsis-ntlp-08 (work in progress), September 2005. [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. 7.2. 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. Fu, et al. Expires April 19, 2006 [Page 7] Internet-Draft GIST over SCTP October 2005 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 Fu, et al. 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