Network Working Group M. Tuexen Internet-Draft I. Ruengeler Intended status: Standards Track Muenster Univ. of Applied Sciences Expires: September 3, 2010 R. Stewart Researcher March 2, 2010 SACK-IMMEDIATELY extension for the Stream Control Transmission Protocol draft-tuexen-tsvwg-sctp-sack-immediately-03.txt Abstract This document defines a method for a sender of a DATA chunk to indicate that the corresponding SACK chunk should be sent back immediately. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 September 3, 2010. Copyright Notice Copyright (c) 2010 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 Tuexen, et al. Expires September 3, 2010 [Page 1] Internet-Draft SACK-IMMEDIATELY March 2010 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 BSD License. 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 . . . . . . . . . . . . . . . 4 5. Interoperability Considerations . . . . . . . . . . . . . . . . 4 6. Socket API Considerations . . . . . . . . . . . . . . . . . . . 4 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9.1. Normative References . . . . . . . . . . . . . . . . . . . 5 9.2. Informative References . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Tuexen, et al. Expires September 3, 2010 [Page 2] Internet-Draft SACK-IMMEDIATELY March 2010 1. Introduction [RFC4960] states that an SCTP implementation should use delayed SACKs. In combination with the Nagle algorithm, reduced congestion windows after timeouts, the handling of the SHUTDOWN-PENDING state, or other situations this might result in reduced performance of the protocol. This document describes a simple extension of the SCTP DATA chunk by defining a new flag, the I-bit. The sender indicates by setting this bit that the corresponding SACK chunk should be sent back without delaying it. 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. 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 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. Tuexen, et al. Expires September 3, 2010 [Page 3] Internet-Draft SACK-IMMEDIATELY March 2010 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. Reasons for setting the I-bit include o The sender has not enough queued user data to send the remaining DATA chunks due to the Nagle algorithm. o The sending of a DATA chunk fills the congestion or receiver window. o The sender is in the SHUTDOWN-PENDING state. o The sender has reduced its RTO.Min such that a retransmission timeout will occur if the receiver delays its SACK. 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. 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] a 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 feature described in this document. 6. Socket API Considerations A socket API implementation based on [I-D.ietf-tsvwg-sctpsocket] SHOULD be extended by supporting a flag called SCTP_SACK_IMMEDIATELY, which can be set in the sinfo_flags field of the struct sctp_sndrcvinfo structure. Tuexen, et al. Expires September 3, 2010 [Page 4] Internet-Draft SACK-IMMEDIATELY March 2010 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 MUST be 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 registeration procedure defined in [I-D.tuexen-tsvwg-sctp-chunk-flags] 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] should be RFCXXXX. 8. Security Considerations This document does not add any additional security considerations in addition to the ones given in [RFC4960]. 9. References 9.1. 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. [I-D.tuexen-tsvwg-sctp-chunk-flags] Tuexen, M. and R. Stewart, "Stream Control Transmission Protocol Chunk Flags Registration", draft-tuexen-tsvwg-sctp-chunk-flags-00 (work in progress), March 2010. 9.2. Informative References [I-D.ietf-tsvwg-sctpsocket] Stewart, R., Poon, K., Tuexen, M., Yasevich, V., and P. Lei, "Sockets API Extensions for Stream Control Tuexen, et al. Expires September 3, 2010 [Page 5] Internet-Draft SACK-IMMEDIATELY March 2010 Transmission Protocol (SCTP)", draft-ietf-tsvwg-sctpsocket-21 (work in progress), February 2010. URIs [1] Authors' Addresses Michael Tuexen Muenster Univ. of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: tuexen@fh-muenster.de Irene Ruengeler Muenster Univ. of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: i.ruengeler@fh-muenster.de Randall R. Stewart Researcher Chapin, SC 29036 USA Phone: Email: randall@lakerest.net Tuexen, et al. Expires September 3, 2010 [Page 6]