draft-ietf-tsvwg-sctp-sack-immediately-02.txt   draft-ietf-tsvwg-sctp-sack-immediately-03.txt 
Network Working Group M. Tuexen Network Working Group M. Tuexen
Internet-Draft I. Ruengeler Internet-Draft I. Ruengeler
Updates: 4960 (if approved) Muenster Univ. of Appl. Sciences Updates: 4960 (if approved) Muenster Univ. of Appl. Sciences
Intended status: Standards Track R. R. Stewart Intended status: Standards Track R. R. Stewart
Expires: September 17, 2013 Adara Networks Expires: October 10, 2013 Adara Networks
March 16, 2013 April 08, 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-02.txt draft-ietf-tsvwg-sctp-sack-immediately-03.txt
Abstract Abstract
This document updates RFC 4960 by defining a method for the sender of This document updates RFC 4960 by defining a method for the sender of
a DATA chunk to indicate that the corresponding SACK chunk should be a DATA chunk to indicate that the corresponding SACK chunk should be
sent back immediately and not be delayed. It is done by specifying a sent back 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 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 either by the SCTP implementation or by the application using an SCTP
stack. Since unknown flags in chunk headers are ignored by SCTP stack. Since unknown flags in chunk headers are ignored by SCTP
implementations, this extension does not introduce any implementations, this extension does not introduce any
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 17, 2013. This Internet-Draft will expire on October 10, 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3 3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Triggering at the Application Level . . . . . . . . . . . 3 4.1. Triggering at the Application Level . . . . . . . . . . . 3
4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 3 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Sender Side Considerations . . . . . . . . . . . . . . . 4 5.1. Sender Side Considerations . . . . . . . . . . . . . . . 4
5.2. Receiver Side Considerations . . . . . . . . . . . . . . 4 5.2. Receiver Side Considerations . . . . . . . . . . . . . . 5
6. Interoperability Considerations . . . . . . . . . . . . . . . 5 6. Interoperability Considerations . . . . . . . . . . . . . . . 5
7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5 7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6
11.2. Informative References . . . . . . . . . . . . . . . . . 6 11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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 and remains the default behavior. receiver of the DATA chunk and remains 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
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/ 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 DATA chunk header. field of the DATA chunk header.
This bit was Reserved in [RFC4960]. [RFC4960] specified that this
bit should be set to 0 by the sender and ignored by the receiver.
4. Use Cases 4. Use Cases
The setting of the I-bit can either be triggered by the application The setting of the I-bit can either be triggered by the application
using SCTP or by the SCTP stack itself. using SCTP or by the SCTP stack itself. The following two
subsections provide a non-exhaustive list of examples.
4.1. Triggering at the Application Level 4.1. Triggering at the Application Level
Upper layers of SCTP using the socket API as defined in [RFC6458] may One example of a situation in which it may be desirable for an
subscribe to the SCTP_SENDER_DRY_EVENT for getting a notification as application to trigger setting of the I-bit involves the
soon as no user data is outstanding anymore. To avoid an unnecessary SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers
delay while waiting for such an event, the application might set the of SCTP using the socket API as defined in [RFC6458] may subscribe to
I-Bit on the last DATA chunk sent before waiting for the event. This the SCTP_SENDER_DRY_EVENT for getting a notification as soon as no
enabling is possible using the extension of the socket API described user data is outstanding anymore. To avoid an unnecessary delay
in Section 7. while waiting for such an event, the application can request the
setting of the I-Bit when sending the last user message before
waiting for the event. This results in setting the I-bit of the last
DATA chunk corresponding to the user message and is possible using
the extension of the socket API described in Section 7.
4.2. Triggering at the SCTP Level 4.2. Triggering at the SCTP Level
There are also situations in which the SCTP implementation can set There are also situations in which the SCTP implementation can set
the I-bit without interacting with the upper layer. the I-bit without interacting with the upper layer.
If the association is in the SHUTDOWN-PENDING state, the I-bit should If the association is in the SHUTDOWN-PENDING state, setting the
be set. This reduces the number of simultaneous associations in case I-bit reduces the number of simultaneous associations for a busy
of a busy server handling short living associations. server handling short living associations.
Another case is where the sending of a DATA chunk fills the Another case is where the sending of a DATA chunk fills the
congestion or receiver window. Setting the I-bit in these cases congestion or receiver window. Setting the I-bit in these cases
improves the throughput of the transfer. improves the throughput of the transfer.
If an SCTP association supports the SCTP Stream Reconfiguration If an SCTP association supports the SCTP Stream Reconfiguration
extension defined in [RFC6525], the performance can be improved by extension defined in [RFC6525], the performance can be improved by
setting the I-bit when there are pending reconfiguration requests setting the I-bit when there are pending reconfiguration requests
requiring no outstanding DATA chunks. that require that there be no outstanding DATA chunks.
5. Procedures 5. Procedures
5.1. Sender Side Considerations 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.
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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].
5.2. 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 send it back immediately. SACK chunk, i.e., the receiver SHOULD immediately respond with the
corresponding SACK chunk.
6. 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.
7. Socket API Considerations 7. Socket API Considerations
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Please note that this section is informational only. Please note that this section is informational only.
A socket API implementation based on [RFC6458] needs to be extended A socket API implementation based on [RFC6458] needs to be extended
to allow the application to set the I-bit of the last DATA chunk when to allow the application to set the I-bit of the last DATA chunk when
sending each user message. sending each user message.
This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in
the snd_flags field of the struct sctp_sndinfo structure when using the snd_flags field of the struct sctp_sndinfo structure when using
sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo
structure is used instead when calling sctp_send(), sctp_sendx(), or structure is used instead when calling sctp_send(), sctp_sendx(), or
sendmsg(), the SCTP_SACK_IMMEDIATELY flags can be set in the sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be set in the
sinfo_flags field. When using the deprecated function sctp_sendmsg() sinfo_flags field. When using the deprecated function sctp_sendmsg()
the SCTP_SACK_IMMEDIATELY flag can be in the flags parameter. the SCTP_SACK_IMMEDIATELY flag can be in the flags parameter.
8. 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 and the reference should be RFCXXXX.
chunk flags table for the DATA chunk should be RFCXXXX.
This requires an update of the "DATA Chunk Flags" registry for SCTP:
DATA Chunk Flags
+------------------+-----------------+-----------+
| Chunk Flag Value | Chunk Flag Name | Reference |
+------------------+-----------------+-----------+
| 0x01 | E bit | [RFC4960] |
| 0x02 | B bit | [RFC4960] |
| 0x04 | U bit | [RFC4960] |
| 0x08 | I Bit | [RFCXXXX] |
| 0x10 | Unassigned | |
| 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+
9. Security Considerations 9. Security Considerations
This document does not add any additional security considerations in See [RFC4960] for general security considerations for SCTP. In
addition to the ones given in [RFC4960]. It should be noted that a addition, a malicious sender can force its peer to send packets
malicious sender can force its peer to send packets containing a SACK containing a SACK chunk for each received packet containing DATA
chunk for each received packet containing DATA chunks instead of chunks instead of every other. This could impact the network,
every other. This could impact the network, resulting in more resulting in more packets sent on the network, or the peer because
packets sent on the network, or the peer because the generating and the generating and sending of the packets has some processing cost.
sending of the packets has some processing cost. However, the However, the additional packets can only contain the most simplest
additional packets can only contain the most simplest SACK chunk (no SACK chunk (no gap reports, no duplicate TSNs), since in case of
gap reports, no duplicate TSNs), since in case of packet drop or packet drop or reordering in the network a SACK chunk would be sent
reordering in the network a SACK chunk would be sent immediately immediately anyway. Therefore this does neither introduce a
anyway. Therefore this does neither introduce a significant significant additional processing cost on the receiver side nor does
additional processing cost on the receiver side nor does it cause it cause congestion on the network.
congestion on the network.
10. Acknowledgments 10. Acknowledgments
The authors wish to thank Mark Allmann, Brian Bidulock, Gorry The authors wish to thank Mark Allmann, Brian Bidulock, David Black,
Fairhurst, Janardhan Iyengar, and Kacheong Poon for their invaluable Anna Brunstrom, Gorry Fairhurst, Janardhan Iyengar, Kacheong Poon,
comments. and Michael Welzl for their invaluable comments.
11. References 11. References
11.1. 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", RFC [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007. 4960, September 2007.
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