Network Working Group M. Tuexen Internet-Draft I. Ruengeler Intended status: Standards Track Muenster Univ. of Appl. Sciences Expires: September 15, 2013 R. R. Stewart Adara Networks March 14, 2013 SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol draft-ietf-tsvwg-sctp-sack-immediately-01.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. It is done by specifying a bit in the DATA chunk header, called the I-bit, which can get set either by the SCTP implementation or by the application using an SCTP stack. 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. 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Expires September 15, 2013 [Page 1] Internet-Draft SACK-IMMEDIATELY March 2013 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. Triggering at the Application Level . . . . . . . . . . . 3 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 3 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Sender Side Considerations . . . . . . . . . . . . . . . 4 5.2. Receiver Side Considerations . . . . . . . . . . . . . . 4 6. Interoperability Considerations . . . . . . . . . . . . . . . 5 7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 11.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 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 and remains the to be the default behavior. 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. Use-cases are described in Section 4. 2. Conventions Tuexen, et al. Expires September 15, 2013 [Page 2] Internet-Draft SACK-IMMEDIATELY March 2013 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. 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 DATA chunk header. 4. Use Cases The setting of the I-bit can either be triggered by the application using SCTP or by the SCTP stack itself. 4.1. Triggering at the Application Level Upper layers of SCTP using the socket API as defined in [RFC6458] may subscribe to the SCTP_SENDER_DRY_EVENT for getting a notification as soon as no user data is outstanding anymore. To avoid an unnecessary delay while waiting for such an event, the application might set the I-Bit on the last DATA chunk sent before waiting for the event. This enabling is possible using the extension of the socket API described in Section 7. 4.2. Triggering at the SCTP Level Tuexen, et al. Expires September 15, 2013 [Page 3] Internet-Draft SACK-IMMEDIATELY March 2013 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. If an SCTP association supports the SCTP Stream Reconfiguration extension defined in [RFC6525], the performance can be improved by setting the I-bit when there are pending reconfiguration requests requiring no outstanding DATA chunks. 5. Procedures 5.1. 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 (see Section 4 for the benefits): 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 7). o The sender is in the SHUTDOWN-PENDING state. o The sending of a DATA chunk fills the congestion or receiver window. o The sending of an Outgoing SSN Reset Request Parameter or an SSN/ TSN Reset Request Parameter is pending, if the association supports the Stream Reconfiguration extension defined in [RFC6525]. 5.2. 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 send it back immediately. Tuexen, et al. Expires September 15, 2013 [Page 4] Internet-Draft SACK-IMMEDIATELY March 2013 6. 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. 7. Socket API Considerations This section describes how the socket API defined in [RFC6458] 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 [RFC6458] is extended to allow the application to set the I-bit of the last DATA chunk for each provided user message. This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in the snd_flags field of the struct sctp_sndinfo structure when using sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo structure is used instead when calling sctp_send(), sctp_sendx(), or sendmsg(), the SCTP_SACK_IMMEDIATELY flags can be set in the sinfo_flags field. When using the deprecated function sctp_sendmsg() the SCTP_SACK_IMMEDIATELY flag can be in the flags parameter. 8. 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 should be RFCXXXX. 9. Security Considerations This document does not add any additional security considerations in addition to the ones given in [RFC4960] and [RFC6458]. It should be noted that an malicious sender can force its peer to send packets containing SACK chunks for each received packet containing DATA chunks instead of every other. However, every receiver has to be Tuexen, et al. Expires September 15, 2013 [Page 5] Internet-Draft SACK-IMMEDIATELY March 2013 able to do this anyway. It might be configured to do so or has to do this because of packet loss or reordering in the network. 10. Acknowledgments The authors wish to thank Mark Allmann, Brian Bidulock, Gorry Fairhurst, Janardhan Iyengar, and Kacheong Poon for their invaluable comments. 11. References 11.1. 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. 11.2. Informative References [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. [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control Transmission Protocol (SCTP) Stream Reconfiguration", RFC 6525, February 2012. Authors' Addresses Michael Tuexen Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt DE Email: tuexen@fh-muenster.de Tuexen, et al. Expires September 15, 2013 [Page 6] Internet-Draft SACK-IMMEDIATELY March 2013 Irene Ruengeler Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt DE Email: i.ruengeler@fh-muenster.de Randall R. Stewart Adara Networks Chapin, SC 29036 US Email: randall@lakerest.net Tuexen, et al. Expires September 15, 2013 [Page 7]