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Network Working Group L. Wood
Internet-Draft Surrey alumni
Intended status: Experimental W. Eddy
Expires: May 5, 2016 MTI Systems
W. Ivancic
NASA
November 2, 2015


Congestion control for the Saratoga protocol
draft-wood-tsvwg-saratoga-congestion-control-08

Abstract

Saratoga is a data transfer protocol designed to carry potentially
large volumes of data over difficult network paths, often including
only a single high-rate link and only one application flow. As the
requirements for use vary across deployment environments, the base
Saratoga specification only assumes that an implementation will be
able to clock packets out at a configurable rate, and beyond this
specifies no inherent or particular congestion-control behaviour.
The design of Saratoga deliberately supports the integration of
congestion-control algorithms without modification to the base
protocol. This document describes how congestion control can be
supported in the Saratoga transfer protocol. Saratoga is intended
for use in private networks, where its use is engineered as a single
flow to fill a link. However, as Saratoga is implemented over UDP,
it can be multiplexed, and can be run across the public Internet, in
which case congestion control in accordance with the UDP Guidelines
becomes necessary.

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on May 5, 2016.




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Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.

This document may not be modified, and derivative works of it may not
be created, except to format it for publication as an RFC or to
translate it into languages other than English.

Table of Contents

1. Background and Introduction . . . . . . . . . . . . . . . . . 2
2. Approaches to congestion control . . . . . . . . . . . . . . 3
2.1. TCP-friendly rate control . . . . . . . . . . . . . . . . 3
2.2. Explicit Congestion Notification . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5

1. Background and Introduction

The Saratoga data transfer protocol is described in
[draft-wood-tsvwg-saratoga]. Given that Saratoga was originally
developed for scheduled peer-to-peer communications over dedicated
links in private networks, where each application has the entire link
for the duration of its transfer, many Saratoga implementations
deliberately lack any form of congestion control and send at line
rate to maximise throughput and link utilisation in their
environments. Congestion control is necessary for use in the public
Internet, in accordance with the UDP Guidelines [RFC5405]. Newer
Saratoga implementations may use timestamps to perform TCP-Friendly
Rate Control (TFRC) [RFC5348] or other congestion control mechanisms
such as LEDBAT [RFC6817], if appropriate for the environment, and
where simultaneous sharing of capacity with other traffic and
applications is required. Sender-side TFRC for Saratoga has been
shown to be possible without modifications to the Saratoga protocol




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specification, using existing timestamps on selective negative
acknowledgement messages [draft-eddy-tsvwg-saratoga-tfrc].

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 RFC 2119. [RFC2119]

2. Approaches to congestion control

Saratoga can be implemented to perform congestion control at the
sender, based on feedback from acknowledgement STATUS packets, or
have the sender configured to use simple open-loop rate control to
only use a fixed amount of link capacity. Congestion control is
expected to be undesirable for many of Saratoga's use cases and
expected environmental conditions, while simple rate control is
considered useful for some use cases. Use over the public Internet
requires congestion control.

Congestion control MUST be supported and used if Saratoga is being
used across paths that go over the public Internet, and SHOULD be
supported in environments where links in the path are shared by
traffic flows. Congestion control MAY NOT be supported across
private, single-flow links engineered for performance: Saratoga's
primary use case.

2.1. TCP-friendly rate control

Sender-side TCP-friendly rate control can be implemented by mirroring
timestamps in STATUS messages and using the approach outlined in
[draft-eddy-tsvwg-saratoga-tfrc].

Other approaches to TCP-friendly congestion control are possible, and
Saratoga and its selective negative acknowledgements may prove useful
as an implementation testbed for developing and refining new
congestion-control algorithms.

2.2. Explicit Congestion Notification

Supporting Explicit Congestion Notification in a UDP-based protocol
such as Saratoga requires that ECN events be exposed to userspace
applications using UDP via a programming interface. Once such a
programming interface becomes available, providing counts of ECN
events in STATUS and DATA packets will be straightforward. Until
that time, specifying ECN support in more detail is not required.







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3. Security Considerations

Use of effective congestion control mechanisms always raises concerns
about fairness and spoofing or misleading senders - issues not unique
to Saratoga.

4. IANA Considerations

There should be no additional IANA considerations.

5. Acknowledgements

We thank the IETF for reminding us about the importance of congestion
for standards-track protocols.

Work on this document at NASA's Glenn Research Center was funded by
NASA's Earth Science Technology Office (ESTO).

6. References

6.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.

6.2. Informative References

[draft-eddy-tsvwg-saratoga-tfrc]
Eddy, W., Wood, L., and W. Ivancic, "TFRC-based congestion
control for Saratoga", draft-eddy-tsvwg-saratoga-tfrc-08
(work in progress) , November 2015.

[draft-wood-tsvwg-saratoga]
Wood, L., Eddy, W., Smith, C., Ivancic, W., and C.
Jackson, "Saratoga: A Scalable Data Transfer Protocol",
draft-wood-tsvwg-saratoga-18 (work in progress) , November
2015.

[RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification",
RFC 5348, DOI 10.17487/RFC5348, September 2008,
.







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[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405,
DOI 10.17487/RFC5405, November 2008,
.

[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
DOI 10.17487/RFC6817, December 2012,
.

Authors' Addresses

Lloyd Wood
University of Surrey alumni
Sydney, New South Wales
Australia

Email: L.Wood@society.surrey.ac.uk


Wesley M. Eddy
MTI Systems
MS 500-ASRC
NASA Glenn Research Center
21000 Brookpark Road
Cleveland, OH 44135
USA

Phone: +1-216-433-6682
Email: wes@mti-systems.com


Will Ivancic
NASA Glenn Research Center
21000 Brookpark Road, MS 54-5
Cleveland, OH 44135
USA

Phone: +1-216-433-3494
Email: William.D.Ivancic@grc.nasa.gov











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