draft-bensley-tcpm-dctcp-01.txt   draft-bensley-tcpm-dctcp-02.txt 
Network Working Group S. Bensley Network Working Group S. Bensley
Internet-Draft Microsoft Internet-Draft Microsoft
Intended status: Informational L. Eggert Intended status: Informational L. Eggert
Expires: December 7, 2014 NetApp Expires: July 25, 2015 NetApp
D. Thaler D. Thaler
Microsoft Microsoft
June 5, 2014 January 21, 2015
Microsoft's Datacenter TCP (DCTCP): Microsoft's Datacenter TCP (DCTCP):
TCP Congestion Control for Datacenters TCP Congestion Control for Datacenters
draft-bensley-tcpm-dctcp-01 draft-bensley-tcpm-dctcp-02
Abstract Abstract
This memo describes Datacenter TCP (DCTCP), an improvement to TCP This memo describes Datacenter TCP (DCTCP), an improvement to TCP
congestion control for datacenter traffic, as implemented in Windows congestion control for datacenter traffic, as implemented in Windows
Server 2012. DCTCP enhances Explicit Congestion Notification (ECN) Server 2012. DCTCP enhances Explicit Congestion Notification (ECN)
processing to estimate the fraction of bytes that encounter processing to estimate the fraction of bytes that encounter
congestion, rather than simply detecting that some congestion has congestion, rather than simply detecting that some congestion has
occurred. DCTCP then scales the TCP congestion window based on this occurred. DCTCP then scales the TCP congestion window based on this
estimate. This method achieves high burst tolerance, low latency, estimate. This method achieves high burst tolerance, low latency,
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Copyright Notice Copyright Notice
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DCTCP Algorithm . . . . . . . . . . . . . . . . . . . . . . . 3 3. DCTCP Algorithm . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Marking Congestion on the Switch . . . . . . . . . . . . 4 3.1. Marking Congestion on the Switch . . . . . . . . . . . . 4
3.2. Echoing Congestion Information on the Receiver . . . . . 4 3.2. Echoing Congestion Information on the Receiver . . . . . 4
3.3. Processing Congestion Indications on the Sender . . . . . 5 3.3. Processing Congestion Indications on the Sender . . . . . 5
4. Implementation Issues . . . . . . . . . . . . . . . . . . . . 6 4. Implementation Issues . . . . . . . . . . . . . . . . . . . . 7
5. Deployment Issues . . . . . . . . . . . . . . . . . . . . . . 7 5. Deployment Issues . . . . . . . . . . . . . . . . . . . . . . 7
6. Known Issues . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Known Issues . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
Large datacenters necessarily need a large number of network switches Large datacenters necessarily need a large number of network switches
to interconnect the servers in the datacenter. Therefore, a to interconnect the servers in the datacenter. Therefore, a
datacenter can greatly reduce its capital expenditure by leveraging datacenter can greatly reduce its capital expenditure by leveraging
low cost switches. However, low cost switches tend to have limited low cost switches. However, low cost switches tend to have limited
queue capacities and thus are more susceptible to packet loss due to queue capacities and thus are more susceptible to packet loss due to
congestion. congestion.
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aggressively and unnecessarily affects the throughput of long flows. aggressively and unnecessarily affects the throughput of long flows.
Datacenter TCP (DCTCP) enhances ECN processing to estimate the Datacenter TCP (DCTCP) enhances ECN processing to estimate the
fraction of bytes that encounter congestion, rather than simply fraction of bytes that encounter congestion, rather than simply
detecting that some congestion has occurred. DCTCP then scales the detecting that some congestion has occurred. DCTCP then scales the
TCP congestion window based on this estimate. This method achieves TCP congestion window based on this estimate. This method achieves
high burst tolerance, low latency, and high throughput with shallow- high burst tolerance, low latency, and high throughput with shallow-
buffered switches. buffered switches.
This document describes DCTCP as implemented in Microsoft Windows This document describes DCTCP as implemented in Microsoft Windows
Server 2012. Server 2012. Since publication of the first versions of this
document, the Linux [LINUX] and FreeBSD [FREEBSD] operating systems
have also implemented support for DCTCP in a way that is believed to
follow this document.
2. Terminology 2. Terminology
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. DCTCP Algorithm 3. DCTCP Algorithm
There are three components involved in the DCTCP algorithm: There are three components involved in the DCTCP algorithm:
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[ODCTCP] Kato, M., "Improving Transmission Performance with One- [ODCTCP] Kato, M., "Improving Transmission Performance with One-
Sided Datacenter TCP", M.S. Thesis, Keio University, 2014, Sided Datacenter TCP", M.S. Thesis, Keio University, 2014,
<http://eggert.org/students/kato-thesis.pdf>. <http://eggert.org/students/kato-thesis.pdf>.
[ADCTCP] Alizadeh, M., Javanmard, A., and B. Prabhakar, "Analysis [ADCTCP] Alizadeh, M., Javanmard, A., and B. Prabhakar, "Analysis
of DCTCP: Stability, Convergence, and Fairness", June of DCTCP: Stability, Convergence, and Fairness", June
2011, 2011,
<http://simula.stanford.edu/~alizade/Site/DCTCP_files/ <http://simula.stanford.edu/~alizade/Site/DCTCP_files/
dctcp_analysis-full.pdf>. dctcp_analysis-full.pdf>.
[LINUX] Borkmann, D., "Linux DCTCP patch", 2014,
<https://git.kernel.org/cgit/linux/kernel/git/davem/net-
next.git/
commit/?id=e3118e8359bb7c59555aca60c725106e6d78c5ce>.
[FREEBSD] Kato, M., "DCTCP (Data Center TCP) implementation", 2015,
<https://github.com/freebsd/freebsd/
commit/8ad879445281027858a7fa706d13e458095b595f>.
Authors' Addresses Authors' Addresses
Stephen Bensley Stephen Bensley
Microsoft Microsoft
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
USA USA
Phone: +1 425 703 5570 Phone: +1 425 703 5570
Email: sbens@microsoft.com Email: sbens@microsoft.com
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