draft-ietf-tsvwg-sctp-sack-immediately-00.txt   draft-ietf-tsvwg-sctp-sack-immediately-01.txt 
Network Working Group M. Tuexen Network Working Group M. Tuexen
Internet-Draft I. Ruengeler Internet-Draft I. Ruengeler
Intended status: Standards Track Muenster Univ. of Appl. Sciences Intended status: Standards Track Muenster Univ. of Appl. Sciences
Expires: August 20, 2013 R. Stewart Expires: September 15, 2013 R. R. Stewart
Adara Networks Adara Networks
February 16, 2013 March 14, 2013
SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol
draft-ietf-tsvwg-sctp-sack-immediately-00.txt draft-ietf-tsvwg-sctp-sack-immediately-01.txt
Abstract Abstract
This document defines a method for the sender of a DATA chunk to This document defines a method for the sender of a DATA chunk to
indicate that the corresponding SACK chunk should be sent back indicate that the corresponding SACK chunk should be sent back
immediately and not be delayed. 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 Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 20, 2013. This Internet-Draft will expire on September 15, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . . 4 3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Sender Side Considerations . . . . . . . . . . . . . . . . 4 4.1. Triggering at the Application Level . . . . . . . . . . . 3
4.2. Receiver Side Considerations . . . . . . . . . . . . . . . 5 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 3
5. Interoperability Considerations . . . . . . . . . . . . . . . . 5 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Socket API Considerations . . . . . . . . . . . . . . . . . . . 5 5.1. Sender Side Considerations . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5.2. Receiver Side Considerations . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. Interoperability Considerations . . . . . . . . . . . . . . . 5
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . . 6 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . . 6 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6
11.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
According to [RFC4960] the receiver of a DATA chunk should use According to [RFC4960] the receiver of a DATA chunk should use
delayed SACKs. This delaying is completely controlled by the delayed SACKs. This delaying is completely controlled by the
receiver of the DATA chunk. receiver of the DATA chunk and remains the to be the default
behavior.
In specific situations the delaying of SACKs results in reduced In specific situations the delaying of SACKs results in reduced
performance of the protocol. If such a situation can be detected by performance of the protocol. If such a situation can be detected by
the receiver, the corresponding SACK can be sent immediately. For the receiver, the corresponding SACK can be sent immediately. For
example, [RFC4960] recommends the immediate sending if the receiver example, [RFC4960] recommends the immediate sending if the receiver
has detected message loss or message duplication. However, if the has detected message loss or message duplication. However, if the
situation can only be detected by the sender of the DATA chunk, situation can only be detected by the sender of the DATA chunk,
[RFC4960] provides no method of avoiding the delaying of the SACK. [RFC4960] provides no method of avoiding the delaying of the SACK.
Thus the protocol performance might be reduced. Thus the protocol performance might be reduced.
This document overcomes this limitation and describes a simple This document overcomes this limitation and describes a simple
extension of the SCTP DATA chunk by defining a new flag, the I-bit. 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 The sender of a DATA chunk indicates by setting this bit that the
corresponding SACK chunk should not be delayed. corresponding SACK chunk should not be delayed. Use-cases are
described in Section 4.
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 6.
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.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. The I-bit in the DATA Chunk Header 3. The I-bit in the DATA Chunk Header
The following Figure 1 shows the extended DATA chunk. The following Figure 1 shows the extended DATA chunk.
0 1 2 3 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 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
skipping to change at page 4, line 29 skipping to change at page 3, line 32
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ User Data / / User Data /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended DATA chunk format Figure 1: Extended DATA chunk format
The only difference between the DATA chunk in Figure 1 and the DATA 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 chunk defined in [RFC4960] is the addition of the I-bit in the flags
field of the chunk header. field of the DATA chunk header.
4. Procedures 4. Use Cases
4.1. Sender Side Considerations 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
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 Whenever the sender of a DATA chunk can benefit from the
corresponding SACK chunk being sent back without delay, the sender 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 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. 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 Reasons for setting the I-bit include, but are not limited to, the
following: following (see Section 4 for the benefits):
o The application requests to set the I-bit of the last DATA chunk 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 of a user message when providing the user message to the SCTP
implementation (see Section 6). implementation (see Section 7).
o The sender is in the SHUTDOWN-PENDING state. o The sender is in the SHUTDOWN-PENDING state.
o The sending of a DATA chunk fills the congestion or receiver o The sending of a DATA chunk fills the congestion or receiver
window. window.
o The sending of an Outgoing SSN Reset Request Parameter or an SSN/ o The sending of an Outgoing SSN Reset Request Parameter or an SSN/
TSN Reset Request Parameter is pending, if the association TSN Reset Request Parameter is pending, if the association
supports the Stream Reconfiguration extension defined in supports the Stream Reconfiguration extension defined in
[RFC6525]. [RFC6525].
4.2. Receiver Side Considerations 5.2. Receiver Side Considerations
On reception of an SCTP packet containing a DATA chunk with the I-bit 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 set, the receiver SHOULD NOT delay the sending of the corresponding
SACK chunk and SHOULD send it back immediately. SACK chunk and send it back immediately.
5. Interoperability Considerations 6. Interoperability Considerations
According to [RFC4960] the receiver of a DATA chunk with the I-bit 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 set should ignore this bit when it does not support the extension
described in this document. Since the sender of the DATA chunk is described in this document. Since the sender of the DATA chunk is
able to handle this case, there is no requirement for negotiating the able to handle this case, there is no requirement for negotiating the
support of the feature described in this document. support of the feature described in this document.
6. Socket API Considerations 7. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to set the I-bit. extended to provide a way for the application to set the I-bit.
Please note that this section is informational only. Please note that this section is informational only.
A socket API implementation based on [RFC6458] is extended by A socket API implementation based on [RFC6458] is extended to allow
supporting a flag called SCTP_SACK_IMMEDIATELY, which can be set in the application to set the I-bit of the last DATA chunk for each
the snd_flags field of the struct sctp_sndinfo structure or the provided user message.
sinfo_flags field of the struct sctp_sndrcvinfo structure, which is
deprecated.
If the SCTP_SACK_IMMEDIATELY flag is set when sending a user message, This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in
the I-bit of the last DATA chunk of the corresponding user message is the snd_flags field of the struct sctp_sndinfo structure when using
set. 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.
7. IANA Considerations 8. IANA Considerations
[NOTE to RFC-Editor: [NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this "RFCXXXX" is to be replaced by the RFC number you assign this
document. document.
] ]
Following the chunk flag registration procedure defined in [RFC6096] Following the chunk flag registration procedure defined in [RFC6096]
IANA should register a new bit, the I-bit, for the DATA chunk. The 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 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] chunk flags table for the DATA chunk should be RFCXXXX.
should be RFCXXXX.
8. Security Considerations 9. Security Considerations
This document does not add any additional security considerations in This document does not add any additional security considerations in
addition to the ones given in [RFC4960] and [RFC6458]. 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
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.
9. Acknowledgments 10. Acknowledgments
The authors wish to thank Mark Allmann, Brian Bidulock, Janardhan The authors wish to thank Mark Allmann, Brian Bidulock, Gorry
Iyengar, and Kacheong Poon for their invaluable comments. Fairhurst, Janardhan Iyengar, and Kacheong Poon for their invaluable
comments.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
RFC 4960, September 2007. 4960, September 2007.
[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096, Protocol (SCTP) Chunk Flags Registration", RFC 6096,
January 2011. January 2011.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control 11.2. Informative References
Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, February 2012.
10.2. Informative References
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011. Transmission Protocol (SCTP)", RFC 6458, December 2011.
URIs [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", RFC
[1] <http://www.iana.org/assignments/sctp-parameters> 6525, February 2012.
Authors' Addresses Authors' Addresses
Michael Tuexen Michael Tuexen
Muenster University of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
DE DE
Email: tuexen@fh-muenster.de Email: tuexen@fh-muenster.de
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