Network Working Group M. Tuexen Internet-Draft Muenster Univ. of Appl. Sciences Intended status: Standards Track R. Seggelmann Expires: November 30, 2014 T-Systems International GmbH R. Stewart Adara Networks S. Loreto Ericsson May 29, 2014 Additional Policies for the Partial Reliability Extension of the Stream Control Transmission Protocol draft-ietf-tsvwg-sctp-prpolicies-03.txt Abstract This document defines two additional policies for the Partial Reliability Extension of the Stream Control Transmission Protocol (PR-SCTP) allowing to limit the number of retransmissions or to prioritize user messages for more efficient send buffer usage. 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 November 30, 2014. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the 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 Tuexen, et al. Expires November 30, 2014 [Page 1] Internet-Draft Additional PR-SCTP Policies May 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Additional PR-SCTP Policies . . . . . . . . . . . . . . . . . 3 3.1. Limited Retransmissions Policy . . . . . . . . . . . . . 3 3.2. Priority Policy . . . . . . . . . . . . . . . . . . . . . 3 4. Socket API Considerations . . . . . . . . . . . . . . . . . . 4 4.1. Data Types . . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Support for Added PR-SCTP Policies . . . . . . . . . . . 4 4.3. Socket Option for Getting the PR-SCTP Status (SCTP_PR_STATUS) . . . . . . . . . . . . . . . . . . . . 5 4.4. Socket Option for Getting and Setting the PR-SCTP Support (SCTP_PR_SUPPORTED) . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The SCTP Partial Reliability Extension (PR-SCTP) defined in [RFC3758] provides a generic method for senders to abandon user messages. The decision to abandon a user message is sender side only and the exact condition is called a PR-SCTP policy. [RFC3758] also defines one particular PR-SCTP policy, called Timed Reliability. This allows the sender to specify a timeout for a user message after which the SCTP stack abandons the user message. This document specifies the following two additional PR-SCTP policies: Limited Retransmission Policy: Allows to limit the number of retransmissions. Priority Policy: Allows to discard lower priority messages if space for higher priority messages is needed in the send buffer. Tuexen, et al. Expires November 30, 2014 [Page 2] Internet-Draft Additional PR-SCTP Policies May 2014 2. Conventions 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 [RFC2119]. 3. Additional PR-SCTP Policies This section defines two new PR-SCTP policies, one in each subsection. Please note that it is REQUIRED to implement [RFC3758], if you want to implement these additional policies. However, these additional policies are OPTIONAL when implementing [RFC3758]. 3.1. Limited Retransmissions Policy Using the Limited Retransmission Policy allows the sender of a user message to specify an upper limit for the number of retransmissions for each DATA chunk of the given user messages. The sender MUST abandon a user message if the number of retransmissions of any of the DATA chunks of the user message would exceed the provided limit. The sender MUST perform all other actions required for processing the retransmission event, like possibly adopting the congestion window and the retransmission timeout. Please note that the number of retransmissions includes both fast and timer based retransmissions. The sender MAY limit the number of retransmissions to 0. This will result in abandoning the message when it would get retransmitted for the first time. The use of this setting provides a service similar to UDP, which also does not perform any retransmissions. The Limited Retransmissions Policy is used for data channels in the WebRTC protocol stack. See [I-D.ietf-rtcweb-data-channel] for more information. 3.2. Priority Policy Using the Priority Policy allows the sender of a user message to specify a priority. When storing a user message in the send buffer while there is not enough available space, the SCTP stack at the sender side MAY abandon other user messages of the same SCTP association with a priority lower than the provided one. The algorithm for selecting the message being abandoned is implementation specific. After lower priority messages have been abandoned high priority messages can be transferred without blocking the send call (if used Tuexen, et al. Expires November 30, 2014 [Page 3] Internet-Draft Additional PR-SCTP Policies May 2014 in blocking mode) or the send call fails (if used in non-blocking mode). The Priority Policy can be used in the IPFIX protocol stack. See [RFC7011] for more information. 4. Socket API Considerations This section describes how the socket API defined in [RFC6458] is extended to support the newly defined PR-SCTP policies, to provide some statistical information and to control the negotiation of the PR-SCTP extension during the SCTP association setup. Please note that this section is informational only. 4.1. Data Types This section uses data types from [IEEE.1003-1G.1997]: uintN_t means an unsigned integer of exactly N bits (e.g. uint16_t). This is the same as in [RFC6458]. 4.2. Support for Added PR-SCTP Policies As defined in [RFC6458], the PR-SCTP policy is specified and configured by using the following sctp_prinfo structure: struct sctp_prinfo { uint16_t pr_policy; uint32_t pr_value; }; When the Limited Retransmission Policy described in Section 3.1 is used, pr_policy has the value SCTP_PR_SCTP_RTX and the number of retransmissions is given in pr_value. For using the Priority Policy described in Section 3.2, pr_policy has the value SCTP_PR_SCTP_PRIO. The priority is given in pr_value. The value of zero is the highest priority and larger numbers in pr_value denote lower priorities. The following table summarizes the possible parameter settings defined in [RFC6458] and this document: Tuexen, et al. Expires November 30, 2014 [Page 4] Internet-Draft Additional PR-SCTP Policies May 2014 +-------------------+---------------------------+---------------+ | pr_policy | pr_value | Specification | +-------------------+---------------------------+---------------+ | SCTP_PR_SCTP_NONE | Ignored | [RFC6458] | | SCTP_PR_SCTP_TTL | Lifetime in ms | [RFC6458] | | SCTP_PR_SCTP_RTX | Number of retransmissions | Section 3.1 | | SCTP_PR_SCTP_PRIO | Priority | Section 3.2 | +-------------------+---------------------------+---------------+ 4.3. Socket Option for Getting the PR-SCTP Status (SCTP_PR_STATUS) This socket option uses IPPROTO_SCTP as its level and SCTP_PR_STATUS as its name. It can only be used with getsockopt(), but not with setsockopt(). The socket option value uses the following structure: struct sctp_prstatus { sctp_assoc_t sprstat_assoc_id; uint64_t sprstat_abandoned_unsent; uint64_t sprstat_abandoned_sent; }; sprstat_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates for which association the user wants the information. It is an error to use SCTP_{CURRENT|ALL|FUTURE}_ASSOC in sprstat_assoc_id. sprstat_abandoned_unsent: The number of user messages which have been abandoned, before any part of the user message could be sent. sprstat_abandoned_sent: The number of user messages which have been abandoned, after a part of the user message has been sent. There are separate counters for unsent and sent user messages because the SCTP_SEND_FAILED_EVENT supports a similar differentiation. Please note that an abandoned large user message requiring an SCTP level fragmentation is reported in the sprstat_abandoned_sent counter as soon as at least one fragment of it has been sent. Therefore each abandoned user message is either counted in sprstat_abandoned_unsent or sprstat_abandoned_sent. If more detailed information about abandoned user messages is required, the subscription to the SCTP_SEND_FAILED_EVENT is recommended. sctp_opt_info() needs to be extended to support SCTP_PR_STATUS. Tuexen, et al. Expires November 30, 2014 [Page 5] Internet-Draft Additional PR-SCTP Policies May 2014 4.4. Socket Option for Getting and Setting the PR-SCTP Support (SCTP_PR_SUPPORTED) This socket option allows the enabling or disabling of the negotiation of PR-SCTP support for future associations. For existing associations it allows to query whether PR-SCTP support was negotiated or not on particular associations. Whether PR-SCTP is enabled or not per default is implementation specific. This socket option uses IPPROTO_SCTP as its level and SCTP_PR_SUPPORTED as its name. It can be used with getsockopt() and setsockopt(). The socket option value uses the following structure defined in [RFC6458]: struct sctp_assoc_value { sctp_assoc_t assoc_id; uint32_t assoc_value; }; assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets, this parameter indicates upon which association the user is performing an action. The special sctp_assoc_t SCTP_FUTURE_ASSOC can also be used, it is an error to use SCTP_{CURRENT|ALL}_ASSOC in assoc_id. assoc_value: A non-zero value encodes the enabling of PR-SCTP whereas a value of 0 encodes the disabling of PR-SCTP. sctp_opt_info() needs to be extended to support SCTP_PR_SUPPORTED. 5. IANA Considerations This document requires no actions from IANA. 6. Security Considerations This document does not add any additional security considerations in addition to the ones given in [RFC4960], [RFC3758], and [RFC6458]. As indicated in the Security Section of [RFC3758], transport layer security in the form of TLS over SCTP (see [RFC3436]) can't be used for PR-SCTP. However, DTLS over SCTP (see [RFC6083]) could be used instead. It should also be noted that using PR-SCTP for an SCTP association doesn't allow that association to behave more aggressively congestion-control wise than an SCTP association not using PR-SCTP. Tuexen, et al. Expires November 30, 2014 [Page 6] Internet-Draft Additional PR-SCTP Policies May 2014 7. Acknowledgments The authors wish to thank Gorry Fairhurst, Karen Egede Nielsen, Ka- Cheong Poon, Irene Ruengeler, Jamal Hadi Salim, and Vlad Yasevich for their invaluable comments. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, May 2004. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. 8.2. Informative References [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer Security over Stream Control Transmission Protocol", RFC 3436, December 2002. [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram Transport Layer Security (DTLS) for Stream Control Transmission Protocol (SCTP)", RFC 6083, January 2011. [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. Yasevich, "Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)", RFC 6458, December 2011. [RFC7011] Claise, B., Trammell, B., and P. Aitken, "Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of Flow Information", STD 77, RFC 7011, September 2013. [I-D.ietf-rtcweb-data-channel] Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channels", draft-ietf-rtcweb-data-channel-09 (work in progress), May 2014. [IEEE.1003-1G.1997] Institute of Electrical and Electronics Engineers, "Protocol Independent Interfaces", IEEE Standard 1003.1G, March 1997. Tuexen, et al. Expires November 30, 2014 [Page 7] Internet-Draft Additional PR-SCTP Policies May 2014 Authors' Addresses Michael Tuexen Muenster University of Applied Sciences Stegerwaldstrasse 39 48565 Steinfurt DE Email: tuexen@fh-muenster.de Robin Seggelmann T-Systems International GmbH Fasanenweg 5 70771 Leinfelden-Echterdingen DE Email: robin.seggelmann@t-systems.com Randall R. Stewart Adara Networks Chapin, SC 29036 US Email: randall@lakerest.net Salvatore Loreto Ericsson Hirsalantie 11 Jorvas 02420 FI Email: Salvatore.Loreto@ericsson.com Tuexen, et al. Expires November 30, 2014 [Page 8]