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Versions: 00 01 02 03 04 05 06 07 08 09 10 draft-ietf-tsvwg-sctp-sack-immediately

Network Working Group                                          M. Tuexen
Internet-Draft                                              I. Ruengeler
Intended status: Standards Track      Muenster Univ. of Applied Sciences
Expires: August 20, 2009                                      R. Stewart
                                                              Researcher
                                                       February 16, 2009


SACK-IMMEDIATELY extension for the Stream Control Transmission Protocol
            draft-tuexen-tsvwg-sctp-sack-immediately-01.txt

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   This Internet-Draft is submitted to IETF in full conformance with the
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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.


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.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5































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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-SENDING 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 would delay its SACK.

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.  IANA Considerations

   There are no actions required from IANA.


7.  Security Considerations

   This document does not add any additional security considerations in
   addition to the ones given in [RFC4960].





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8.  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.


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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