Centre for Advanced Internet Architectures,
Swinburne University of Technology,
Melbourne, Australia
CRICOS number 00111D

19th February, 2010


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OVERVIEW
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The Enhanced Round Trip Time (ERTT) Khelp module provides less noisy RTT
measurements for use by delay and rate based TCP congestion control algorithms.

Robust estimates of RTT are provided even when the receiver uses delayed
acknowledgements, TCP segmentation offload (TSO) or Selective Acknowledgements
(SACK). In depth details about the module's operation have been documented in
CAIA technical report 100219A [1].

The ERTT Khelp module requires that the bundled version of the Modular TCP
Congestion control v0.9.4 and Khelp Framework v0.1.0 patch be applied to the
kernel before it can be used. If the target system has previously been patched
with either the Modular TCP Congestion Control or Khelp Framework patches, these
should be removed before applying the bundled patch. The bundled patch is
available here:

http://caia.swin.edu.au/urp/newtcp/tools/caia_modularcc_v0.9.4_khelp_v0.1.0_bundle_9.x.r203910.patch


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LICENCE
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The FreeBSD ERTT module is released under a BSD licence.

Refer to licence headers in each source file for further details.


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USAGE
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Make sure you have the FreeBSD system sources installed. These can be installed
using sysinstall.

The running system must have the Modular TCP Congestion control v0.9.4
and Khelp Framework v0.1.0 bundled patch applied.

To build the module, simply run:

  make

To load the compiled module into the running kernel, run the following command
as root:

  kldload ./h_ertt.ko

To unload the module from the running kernel, run the following as root:

  kldunload h_ertt

To delete all artifacts created by compiling the module, run:

  make cleandir


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COMPILE TIME CONFIGURATION
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There are currently no compile-time configuration options.


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RUN TIME CONFIGURATION
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There are currently no run-time configuration options.


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KNOWN LIMITATIONS
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Current known limitations of the ERTT Khelp module software:

1. Received SACKs that do not acknowledge new data may effect the accuracy of
the RTT estimate. Revisions to SACK accounting in FreeBSD fix this
problem and will be released soon.


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ACKNOWLEDGEMENTS
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This project has been made possible in part by a grant from the Cisco University
Research Program Fund at Community Foundation Silicon Valley. Testing and
development was further assisted by a grant from the FreeBSD Foundation.


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RELATED READING
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This software was developed as part of the NewTCP research project at
Swinburne University's Centre for Advanced Internet Architectures.
More information on the project is available at:

http://caia.swin.edu.au/urp/newtcp/

A number of software tools and technical reports related to experimental TCP
research in general are available respectively at:

http://caia.swin.edu.au/urp/newtcp/tools.html
http://caia.swin.edu.au/urp/newtcp/papers.html

At the time of writing, the following software tools may be of interest:

Modular TCP Congestion Control for FreeBSD

Khelp Framework for FreeBSD

Vegas congestion control algorithm

Hamilton delay congestion control algorithm

CUBIC congestion control algorithm

H-TCP congestion control algorithm

Statistical Information For TCP Research (SIFTR)

Deterministic Packet Discard (DPD)

At the time of writing, the following reports/papers may be of interest:

[1] provides a detailed technical discussion of the ERTT module, developed to
give improved RTT estimates for use by congestion control algorithms.


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REFERENCES
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[1] D. Hayes, "Timing enhancements to the FreeBSD kernel to support delay and
    rate based TCP mechanisms", CAIA Technical Report 100219A, February 2010.


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AUTHORS
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The ERTT Khelp module was developed by David Hayes whilst working on the NewTCP
research project at Swinburne University's Centre for Advanced Internet
Architectures, Melbourne, Australia.

David Hayes is the current maintainer, and all contact regarding
this module should be directed to him via email: dahayes@swin.edu.au