Network Working Group L. Wood
Internet-Draft Surrey alumni
Intended status: Experimental W. M. Eddy
Expires: October 23, 2013 MTI Systems
W. Ivancic
NASA
April 21, 2013
Congestion control for the Saratoga protocol
draft-wood-tsvwg-saratoga-congestion-control-03
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
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This Internet-Draft will expire on October 23, 2013.
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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 . . . . . . . . . . . . 4
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
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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
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
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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.
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
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification", RFC
5348, September 2008.
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[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405, November
2008.
[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
December 2012.
[draft-eddy-tsvwg-saratoga-tfrc]
Eddy, W.M., Wood, L., and W. Ivancic, "TFRC-based
congestion control for Saratoga", draft-eddy-tsvwg-
saratoga-tfrc-03 (work in progress) , April 2013.
[draft-wood-tsvwg-saratoga]
Wood, L., Eddy, W. M., Smith, C., Ivancic, W., and C.
Jackson, "Saratoga: A Scalable Data Transfer Protocol",
draft-wood-tsvwg-saratoga-13 (work in progress) , April
2013.
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
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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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