wdiff rfc7053.original rfc7053.txt

Network Working Group
Internet Engineering Task Force (IETF) M. Tuexen
Internet-Draft
Request for Comments: 7053 I. Ruengeler
Updates: 4960 (if approved) Muenster Univ. of Appl. Sciences
Intended status:
Category: Standards Track R. Stewart
Expires: March 01, 2014
ISSN: 2070-1721 Adara Networks
August 28,
October 2013

SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol
draft-ietf-tsvwg-sctp-sack-immediately-04.txt

Abstract

This document updates RFC 4960 by defining a method for the sender of
a DATA chunk to indicate that the corresponding SACK Selective
Acknowledgment (SACK) chunk should be sent back immediately and
should not be delayed. It is done by specifying a bit in the DATA
chunk header, called the I-bit, (I)mmediate bit, which can get set
either by either
the SCTP Stream Control Transmission Protocol (SCTP) implementation or by the
application using an SCTP stack. Since unknown flags in chunk
headers are ignored by SCTP implementations, this extension does not
introduce any interoperability problems.

Status of This Memo

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

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
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material or to cite them other than as "work in progress."

This Internet-Draft will expire on March 01, 2014.
http://www.rfc-editor.org/info/rfc7053.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The I-bit (I)mmediate Bit in the DATA Chunk Header . . . . . . . . . . . . . 3
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Triggering at the Application Level . . . . . . . . . . . . 4
4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 4 . 5
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 . 5
5.1. Sender Side Sender-Side Considerations . . . . . . . . . . . . . . . . 5
5.2. Receiver Side Considerations . . . . . . . . . . . . . . 5 . 6
6. Interoperability Considerations . . . . . . . . . . . . . . . 5 . 6
7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5 . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 8

1. Introduction

According to [RFC4960] [RFC4960], the receiver of a DATA chunk should use
delayed SACKs. This delaying delay is completely controlled by the receiver
of the DATA chunk and remains the default behavior.

In specific situations situations, the delaying of SACKs results in reduced
performance of the protocol:

1. If such a situation can be detected by the receiver, the
corresponding SACK can be sent immediately. For example,
[RFC4960] recommends the immediate immediately sending the SACK if the receiver
has detected message loss or message duplication.

2. However, if the situation can only be detected by the sender of
the DATA chunk, [RFC4960] provides no method of avoiding a delay
in sending the SACK. Examples of these situations include ones
which
that require interaction with the application (e.g. (e.g., applications
using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones which that
can be detected by the SCTP stack itself (e.g. (e.g., closing the
association, hitting window limits limits, or resetting streams, see
Section 4.2).

To overcome the limitation described in the second case, this
document describes a simple extension of the SCTP DATA chunk by
defining a new flag, the I-bit. The "I bit". By setting this bit, the sender of
a DATA chunk indicates
by setting this bit that the corresponding SACK chunk should not
be delayed.

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 (I)mmediate 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: Extended DATA chunk format

The only difference between the DATA chunk in Figure 1 and the DATA
chunk defined in [RFC4960] is the addition of the I-bit I bit in the flags
field of the DATA chunk header.

This bit was Reserved in [RFC4960].

[RFC4960] specified defines the Reserved field and specifies that this
bit these bits
should be set to 0 by the sender and ignored by the receiver.

4. Use Cases

The setting of the I-bit I bit can either be triggered by the application
using SCTP or by the SCTP stack itself. The following two
subsections provide a non-exhaustive list of examples. examples of how the I
bit may be set.

4.1. Triggering at the Application Level

One example of a situation in which it may be desirable for an
application to trigger the setting of the I-bit I bit involves the
SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers
of SCTP using that use the socket API as defined in [RFC6458] may subscribe
to the SCTP_SENDER_DRY_EVENT for getting a notification to be notified as soon as no user data
is outstanding anymore. outstanding. To avoid an unnecessary delay
while waiting for such an event, delay, the application can
request that the
setting of the I-Bit I bit be set when sending the last user message
before waiting for the event. This results in setting the I-bit I bit of
the last DATA chunk corresponding to the user message and message; this 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 I bit without interacting with the upper layer.

If the association is in the SHUTDOWN-PENDING state, setting the
I-bit I
bit reduces the number of simultaneous associations for a busy server
handling short living short-lived associations.

Another case is where the sending of a DATA chunk fills the
congestion or receiver window. Setting the I-bit 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 I bit when there are pending reconfiguration requests
that require that there be no outstanding DATA chunks.

5. Procedures

5.1. Sender Side 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 I bit in the DATA chunk header. Please note that it is
irrelevant to the receiver why the
sender has set the I-bit. I bit is irrelevant to the receiver.

Reasons for setting the I-bit I bit include, but are not limited to, the
following to (see
Section 4 for the benefits):

o The application requests to set the I-bit I bit of the last DATA chunk
of a user message when providing the user message to the SCTP
implementation (see Section 7).

o The sender is in the SHUTDOWN-PENDING state.

o The sending of a DATA chunk fills the congestion or receiver
window.

o The sending of an Outgoing SSN Reset Request Parameter or an SSN/
TSN Reset Request Parameter is pending, if the association
supports the Stream Reconfiguration extension defined in
[RFC6525].

5.2. Receiver Side Considerations

On reception

Upon receipt of an SCTP packet containing a DATA chunk with the I-bit I bit
set, the receiver SHOULD NOT delay the sending of the corresponding
SACK chunk, i.e., the receiver SHOULD immediately respond with the
corresponding SACK chunk.

6. Interoperability Considerations

According to [RFC4960] [RFC4960], the receiver of a DATA chunk with the I-bit 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
support of the feature described in this document.

7. Socket API Considerations

This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to set the I-bit. I bit.

Please note that this section is informational only.

A socket API implementation based on [RFC6458] needs to be extended
to allow the application to set the I-bit I bit of the last DATA chunk when
sending each user message.

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
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 flag can be set in the
sinfo_flags field. When using the deprecated function sctp_sendmsg()
sctp_sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be in the flags
parameter.

8. IANA Considerations

[NOTE to RFC-Editor:

"RFCXXXX" is to be replaced by the RFC number you assign this
document.

]

Following the chunk flag registration procedure defined in [RFC6096],
IANA should register has registered a new bit, the I-bit, I bit, for the DATA chunk.

The
suggested value is 0x08 and the reference should be RFCXXXX.

This requires an update of the "DATA Chunk "Chunk Flags" registry for SCTP: SCTP has been updated as described in
the following table.

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 bit | [RFCXXXX] [RFC7053] |
| 0x10 | Unassigned | |
| 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+

9. Security Considerations

See [RFC4960] for general security considerations for SCTP. In
addition, a malicious sender can force its peer to send packets
containing a SACK chunk for each received packet containing DATA
chunks instead of every other. other received packet containing DATA chunks.
This could impact the network, resulting in more packets sent on the
network, or the peer peer, because the generating and sending of the
packets has some processing cost. However, the additional packets
can only contain the most simplest SACK chunk (no gap reports, no
duplicate TSNs), since in case cases of packet drop drops or reordering in the
network a SACK chunk would be sent immediately anyway. Therefore Therefore,
this does neither not introduce a significant additional processing cost on
the receiver side. This also does not result in more traffic in the network than
network, because a receiver that
sends sending a SACK for every packet, which packet is
already permitted.

10. Acknowledgments

The authors wish to thank Mark Allmann, Brian Bidulock, David Black,
Anna Brunstrom, Gorry Fairhurst, Janardhan Iyengar, Kacheong Poon,
and Michael Welzl for their invaluable comments.

11. References

11.1. 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.

[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096,
January 2011.

11.2. Informative References

[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011.

[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, February 2012.

Authors' Addresses

Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
DE

Email:

EMail: tuexen@fh-muenster.de

Irene Ruengeler
Muenster University of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
DE

Email:

EMail: i.ruengeler@fh-muenster.de

Randall R. Stewart
Adara Networks
Chapin, SC 29036
US

Email:

EMail: randall@lakerest.net