Network Working Group M. Tuexen
Internet-Draft I. Ruengeler
Intended status: Standards Track Muenster Univ. of Applied Sciences
Expires: January 6, 2009 R. Stewart
The Resource Group
July 5, 2008
SACK-IMMEDIATELY extension for the Stream Control Transmission Protocol
draft-tuexen-tsvwg-sctp-sack-immediately-00.txt
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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.
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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
Intellectual Property and Copyright Statements . . . . . . . . . . 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-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
The Resource Group
1700 Pennsylvania Ave NW
Suite 56
Washington, DC 20006
USA
Phone:
Email: randall.stewart@trgworld.com
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