Network Working Group M. Tuexen Internet-Draft I. Ruengeler Intended status: Standards Track Muenster Univ. of Appl. Sciences Expires: March 5, 2012 R. Stewart Adara Networks September 2, 2011 SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol draft-tuexen-tsvwg-sctp-sack-immediately-07.txt Abstract This document defines a method for the sender of a DATA chunk to indicate that the corresponding SACK chunk should be sent back immediately and not be delayed. 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 March 5, 2012. Copyright Notice Copyright (c) 2011 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 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. Tuexen, et al. Expires March 5, 2012 [Page 1] Internet-Draft SACK-IMMEDIATELY September 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . . 3 4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Sender Side Considerations . . . . . . . . . . . . . . . . 4 4.2. Receiver Side Considerations . . . . . . . . . . . . . . . 5 5. Interoperability Considerations . . . . . . . . . . . . . . . . 5 6. Socket API Considerations . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 10.1. Normative References . . . . . . . . . . . . . . . . . . . 6 10.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Tuexen, et al. Expires March 5, 2012 [Page 2] Internet-Draft SACK-IMMEDIATELY September 2011 1. Introduction According to [RFC4960] the receiver of a DATA chunk should use delayed SACKs. This delaying is completely controlled by the receiver of the DATA chunk. In specific situations the delaying of SACKs results in reduced performance of the protocol. If such a situation can be detected by the receiver, the corresponding SACK can be sent immediately. For example, [RFC4960] recommends the immediate sending if the receiver has detected message loss or message duplication. However, if the situation can only be detected by the sender of the DATA chunk, [RFC4960] provides no method of avoiding the delaying of the SACK. Thus the protocol performance might be reduced. This document overcomes this limitation and describes a simple extension of the SCTP DATA chunk by defining a new flag, the I-bit. The sender of a DATA chunk indicates by setting this bit that the corresponding SACK chunk should not be delayed. Some upper layers of SCTP (see [RFC6083], for example) stop sending further user messages until all sent user messages have been acknowledged by the SCTP peer. Delaying the SACK would result in a longer pause of sending user messages. Because setting the I-bit in these cases involves the upper layer, this document provides an socket API extension. There are also situations in which the SCTP implementation can set the I-bit without interacting with the upper layer. If the association is in the SHUTDOWN-PENDING state, the I-bit should be set. This reduces the number of simultaneous associations in case of a busy server handling short living associations. Another case is where the sending of a DATA chunk fills the congestion or receiver window. Setting the I-bit in these cases improves the throughput of the transfer. 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. The I-bit in the DATA Chunk Header The following Figure 1 shows the extended DATA chunk. Tuexen, et al. Expires March 5, 2012 [Page 3] Internet-Draft SACK-IMMEDIATELY September 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0 | Res |I|U|B|E| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TSN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Stream Identifier | Stream Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Protocol Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / User Data / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Extended DATA chunk format The only difference between the DATA chunk in Figure 1 and the DATA chunk defined in [RFC4960] is the addition of the I-bit in the flags field of the chunk header. 4. Procedures 4.1. Sender Side Considerations Whenever the sender of a DATA chunk can benefit from the corresponding SACK chunk being sent back without delay, the sender MAY set the I-bit in the DATA chunk header. Please note that it is irrelevant to the receiver why the sender has set the I-bit. Reasons for setting the I-bit include but are not limited to the following: o The application requests to set the I-bit of the last DATA chunk of a user message when providing the user message to the SCTP implementation (see Section 6). o The sender is in the SHUTDOWN-PENDING state. o The sending of a DATA chunk fills the congestion or receiver window. Tuexen, et al. Expires March 5, 2012 [Page 4] Internet-Draft SACK-IMMEDIATELY September 2011 4.2. Receiver Side Considerations On reception of an SCTP packet containing a DATA chunk with the I-bit set, the receiver SHOULD NOT delay the sending of the corresponding SACK chunk and SHOULD send it back immediately. 5. Interoperability Considerations According to [RFC4960] the receiver of a DATA chunk with the I-bit set should ignore this bit when it does not support the extension described in this document. Since the sender of the DATA chunk is able to handle this case, there is no requirement for negotiating the support of the feature described in this document. 6. Socket API Considerations This section describes how the socket API defined in [I-D.ietf-tsvwg-sctpsocket] is extended to provide a way for the application to set the I-bit. Please note that this section is informational only. A socket API implementation based on [I-D.ietf-tsvwg-sctpsocket] is extended by supporting a flag called SCTP_SACK_IMMEDIATELY, which can be set in the snd_flags field of the struct sctp_sndinfo structure or the sinfo_flags field of the struct sctp_sndrcvinfo structure, which is deprecated. If the SCTP_SACK_IMMEDIATELY flag is set when sending a user message, the I-bit of the last DATA chunk of the corresponding user message is set. 7. IANA Considerations [NOTE to RFC-Editor: "RFCXXXX" is to be replaced by the RFC number you assign this document. ] Following the chunk flag registration procedure defined in [RFC6096] IANA should register a new bit, the I-bit, for the DATA chunk. The suggested value is 0x08. The reference for the new chunk flag in the chunk flags table for the DATA chunk available at sctp-parameters [1] Tuexen, et al. Expires March 5, 2012 [Page 5] Internet-Draft SACK-IMMEDIATELY September 2011 should be RFCXXXX. 8. Security Considerations This document does not add any additional security considerations in addition to the ones given in [RFC4960]. 9. Acknowledgments The authors wish to thank Mark Allmann, Brian Bidulock, and Kacheong Poon for their invaluable comments. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission Protocol (SCTP) Chunk Flags Registration", RFC 6096, January 2011. 10.2. Informative References [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram Transport Layer Security (DTLS) for Stream Control Transmission Protocol (SCTP)", RFC 6083, January 2011. [I-D.ietf-tsvwg-sctpsocket] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. Yasevich, "Sockets API Extensions for Stream Control Transmission Protocol (SCTP)", draft-ietf-tsvwg-sctpsocket-31 (work in progress), August 2011. URIs [1] Tuexen, et al. Expires March 5, 2012 [Page 6] Internet-Draft SACK-IMMEDIATELY September 2011 Authors' Addresses Michael Tuexen Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: tuexen@fh-muenster.de Irene Ruengeler Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: i.ruengeler@fh-muenster.de Randall R. Stewart Adara Networks Chapin, SC 29036 USA Email: randall@lakerest.net Tuexen, et al. Expires March 5, 2012 [Page 7]