Network Working Group X. Fu Internet-Draft C. Dickmann Expires:
December 20, 2006September 5, 2007 University of Goettingen J. Crowcroft University of Cambridge June 18, 2006March 4, 2007 General Internet Signaling Transport (GIST) over SCTP draft-ietf-nsis-ntlp-sctp-00.txtdraft-ietf-nsis-ntlp-sctp-01.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 December 20, 2006.September 5, 2007. Copyright Notice Copyright (C) The Internet Society (2006).IETF Trust (2007). 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 theadvantage of features provided by SCTP, namely streaming-based transport, support of multiple streams to avoid head of line blocking, and the support of multi-homing to provide network level fault tolerance. Additionally, the support for some extensions of SCTP is also discussed, namely itsthe Partial Reliability Extension and the usageof TLS over SCTP.SCTP is discussed. 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 SCTP3.1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 4 18.104.22.168.2. Protocol-Definition: Forwards-SCTP . . . . . . . . . . 4 3.2. Effect on GIST State Maintenance . . . . . . . . . . . . . 5 22.214.171.124. PR-SCTP Support . . . . . . . . . . . . . . . . . . . . . 5 3.5.6 3.4. API between GIST and NSLP . . . . . . . . . . . . . . . . 5 126.96.36.199 3.4.1. SendMessage . . . . . . . . . . . . . . . . . . . . . 6 188.8.131.52.4.2. NetworkNotification . . . . . . . . . . . . . . . . . 6 3.6. TLS over SCTP Support4. Bit-Level Formats . . . . . . . . . . . . . . . . . . 6 4. Bit-Level Formats. . . . 7 4.1. MA-Protocol-Options . . . . . . . . . . . . . . . . . . . 7 4.1. MA-Protocol-Options5. Application of GIST over SCTP . . . . . . . . . . . . . . . . 7 5.1. Multi-homing support of SCTP . . . . . . . . . . . . . . . 7 5.6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6.8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7.8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8.8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 184.108.40.206. Normative References . . . . . . . . . . . . . . . . . . . 8 220.127.116.11. Informative References . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . . . 10 1. Introduction This document describes the usage of the General Internet Signaling Transport (GIST) protocol  over the Stream Control Transmission Protocol (SCTP) . 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)  for signaling message transport. However, some NSLP context information has a definite lifetime, therefore, the GIST transport protocol must accommodatecould benefit from 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) as an optional transport protocol for GIST, especially if deployment over the public Internet is contemplated. Like TCP, SCTP supports reliability, congestion control,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. In addition, its Partial Reliability extension (PR-SCTP)  supports partial retransmission based on a programmable retransmission timer. This document defines the use of SCTP as a transport protocol for GIST Messaging Associations and discusses the implications on GIST State Maintenance and API between GIST and NSLPs. Furturemore, this document shows how GIST should be used with SCTPto provide thesethe additional features offered by SCTP to deliver the GIST C-mode messages (which can in turn carry NSIS Signaling Layer Protocol (NSLP)  messages as payload). More specifically: howo How to use the multiple streams feature of SCTP. howo How to handleuse the message oriented naturePR-SCTP extention of SCTP. howo How to take theadvantage of the multi-homing support of SCTP. Additionally, this document also discusses how to support two extensions of SCTP, namely PR-SCTP  and TLS over SCTP .The method described in this document does not require any changes of GIST or SCTP. It is only required thatHowever, SCTP implementations MUST 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 .. Other terminologies and abbreviations used in this document are taken from related specifications (e.g.,  and ) as follows: o TLS - Transport Layer Security oSCTP - 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 3.1.1. Overview The basic GIST protocol specification defines two possible protocols to be used in message associations,Messaging 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 recognizeA formal definition of Forwards-SCTP is given in the following section. 3.1.2. Protocol-Definition: Forwards-SCTP MA- Protocol-ID type, and interpret itThis MA-Protocol-ID denotes a basic use of SCTP between peers. Support for the transportthis protocol negotiation during the GIST MA setup handshake (e.g., whether SCTP runs alone or together with TLS). In turn, the "MA-protocol-options" field for Forwards-SCTP needs to be defined for the Stack-Configuration-Data object defined by 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 valueis not includedOPTIONAL. If this protocol is offered, MA-protocol-options data MUST also be carried in the proposal and in addition implementations should only accept reasonable RTO proposals.SCD object. The MA-protocol-options field formats are: o in a Query: 4 byte RTO initial value and 4 byte RTO maximum valueno information apart from the field header. o in a Response: 4 byte RTO initial value, 4 byte RTO maximum value and2 byte port number at which the connection will be accepted. 3.3. Effect on GIST State Maintenance A GIST MAaccepted, followed by 2 pad bytes. The connection is established overopened in the forwards direction, from the querying node towards the responder. The querying node MAY use any source address and source port. The destination information 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. Associations using Forwards-SCTP can carry messages with the transfer attribute Reliable=True. If an error occurs on the SCTP association, which comprises one or more SCTP streams. Each ofconnection such streamsas a reset, as can be useddetected for one or multiple sessions (i.e., one or more MRSs). After completingexample by a socket exception condition, GIST MA setup, which implicitly establishesMUST report this to NSLPs as discussed in Section 4.1.2 of . 3.2. Effect on GIST State Maintenance This document defines the use of SCTP as a bi-directionaltransport protocol for GIST Messaging Associations. As SCTP stream, C-mode messages can be sentprovides additional functionality over TCP, this section dicusses the implications of using GIST over SCTP associationon GIST State Maintenance. While SCTP defines uni-directional streams, for the purpose of this document, the concept of a bi-direction stream is used. Implementations MUST establish downstream and upstream (uni- directional) SCTP streams always together and use the same stream identifier in either direction.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 easypossible to maintain sequencing of messages that affect the same resourceuse different SCTP streams for different resources (e.g., the samedifferent NSLP session),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). 3.4.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  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. 18.104.22.168. 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 are repeatet from  to improve readability, but  remains authoritative. 22.214.171.124.4.1. 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  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. 126.96.36.199.4.2. 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 analog to GIST using TLS over TCP. Thus, TLS over SCTP is triggered by a protocol stack consisting of the Forwards-SCTP MA-protocol-ID and the TLS MA-protocol-ID (, Section 5.7.3). The GIST specification defines the versions of TLS that can be used, as well as the authentication model. All these aspects are not changed by this document and remain valid for TLS over SCTP. Regarding GIST implementations, no special treatment is required in the case of TLS over SCTP in contrastevent to the existing TLS over TCP case. However,NSLP by calling the NetworkNotification primitive with Network-Notification-Type "Routing Status Change". This notification should be done even if SCTP and TLS implementations needwas able to provide a TLS over SCTP service as descriped in . One should note thatremain an SCTP association with TLS support takes advantages of SCTP, such as multi-streaming and multi-homing.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 (see Section 3.2).GIST. 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 msecSCTP 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 anyway to cope with the route change. Nevertheless, 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. 6. Security Considerations The security considerations of both  and  apply. Further security analysis is needed to consider any additional security vulnerabilities, and will be included in an updated draft. 6.7. IANA Considerations A new MA-Protocol-ID (Forwards-SCTP) needs to be assigned, with a recommended value of 3. 7.8. Acknowledgments The authors would like to thank John Loughney, Robert HancockHancock, Andrew McDonald, Fang-Chun Kuo and Jan Demter for their helpful suggestions. 8.9. References 188.8.131.52. Normative References  Schulzrinne, H. and R. Hancock, "GIST: General Internet SignalingSignalling Transport", draft-ietf-nsis-ntlp-09draft-ietf-nsis-ntlp-12 (work in progress), February 2006.March 2007.  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.  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, May 2004.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 184.108.40.206. Informative References  Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981.  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, May 2004. Hancock, R., Karagiannis, G., Loughney, J., and S. Van den Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080, June 2005.  Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer Security over Stream Control Transmission Protocol", RFC 3436, December 2002.Authors' Addresses Xiaoming Fu University of Goettingen Institute for Informatics Lotzestr. 16-18 Goettingen 37083 Germany Email: firstname.lastname@example.org Christian Dickmann University of Goettingen Institute for Informatics Lotzestr. 16-18 Goettingen 37083 Germany Email: email@example.com Jon Crowcroft University of Cambridge Computer Laboratory William Gates Building 15 JJ Thomson Avenue Cambridge CB3 0FD UK Email: firstname.lastname@example.org Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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