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Versions: 00 01 02 03 04 05 06 07 08 09 draft-ietf-tsvwg-sctp-sack-immediately

Network Working Group                                          M. Tuexen
Internet-Draft                                              I. Ruengeler
Updates: 4960 (if approved)           Muenster Univ. of Applied Sciences
Intended status: Standards Track                              R. Stewart
Expires: January 11, 2010                                     Researcher
                                                           July 10, 2009


SACK-IMMEDIATELY extension for the Stream Control Transmission Protocol
            draft-tuexen-tsvwg-sctp-sack-immediately-02.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 11, 2010.

Copyright Notice

   Copyright (c) 2009 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
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   Please review these documents carefully, as they describe your rights
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Abstract

   This document defines a method for a sender of a DATA chunk to



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   indicate that the corresponding SACK chunk should be sent back
   immediately.


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































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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.





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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.




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   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.

   ]

   IANA should change the Reference in the CHUNK TYPES Registry
   available at sctp-parameters [1] for the ID value '0' and Chunk Type
   'Payload Data (DATA)' from RFC4960 to 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.

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
              Transmission Protocol (SCTP)",
              draft-ietf-tsvwg-sctpsocket-19 (work in progress),
              February 2009.

URIs

   [1]  <http://www.iana.org/assignments/sctp-parameters>




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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
























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