Internet DRAFT - draft-manjunath-ipfix-shifted-feedback
draft-manjunath-ipfix-shifted-feedback
INTERNET-DRAFT Manjunath Iyer
Expires: December 18, 2006 Celstream
June 18, 2006
Shifted feedback technique for congestion notification
draft-manjunath-ipfix-shifted-feedback-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The [RFC2581] provides a mechanism to indicate the congestion
information of the network to the source. In this draft, time
shifting of the signal before usage is suggested. The time
shifting operation effectively counters the impact of the self
similarity of the traffic that originates in a DiffServe network
model as a result of the aggregation.
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1. Introduction
1.1 Terminology
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].
1.2 Overview
In a TCP network, a feedback signal indicating the network status
is provided from the end user of the information to the source
as given in [RFC2581]. Although the signal can be effectively
utilized for adjusting the TCP window size and control the traffic
effectively, by the time the signal reaches the source, the network
characteristics would change [RFC2488]. The draft uses a predicted
feedback signal.The formula for computing the TCP window width is
given in[WYX01]
Logically, it would be correct to synchronize the loss probability
and the packet size that exist at any instance of time t. Prediction
of the loss rate would be required to be used in the formula.
1.3 Signal processing with the feedback signal
The network traffic makes use of DiffServ defined in [RFC2474] for
meeting the service quality requirements. The DiffServ involves
aggregation of the traffic resulting in self similarity and long
range dependency in the traffic. The self similar traffic is found
to have adverse effect on the network resources making it tougher
to meet the quality of service (QoS). Shaping the feedback
signal provides an opportunity to counter the impact of the
aggregation and self similarity in the traffic.
1.4. Impact on the resources
The shifted feedback signal can foresee the evolving network and
control the data transfer rates in such a way that the network
does nor get congested and at the same time the resources are
used efficiently. Pumping in packets to a choked network results
in further delays and retransmissions. The signal processing
SHOULD consider both these factors.
One of the simplest processing over the feedback signal is to
control the shifts. When the prediction is done with a time
shift equal to the round trip time (RTT), the value going in
to the formula matches and the resource utilization would be
maximum. It results in reduced packet loss,reduced delay and
jitter that is extremely useful for real time audio or video
traffic. For a time shift less thane RTT the advantage would
be reduced proportionally.
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The RTT value may be deduced from the feedback signal with
the usage of time stamps. The usage of time stamps is given
in [RFC3161]. The predicted value of RTT may be used to compute
the predicted value of the signal over that time duration.
One advantage of the self similarity in the traffic is that
the traffic shaper introduced in such a loop would be self similar.
All the parameters such as RTT would start becoming self similar
and easily predictable. In case where RTT can not be computed, or
computationally expensive, a constant value may be assumed.
2. Implementation
Various implementation models are possible depending up on the
accuracy of the required feedback suitable for the context.
In a client server model the predictions may be done at the client
end and then embedded in the feedback signal.It would reduce the
burden on the server that has to handle multiple streams.
In a duplex peer to per model, still the originator of the feedback
MAY take the responsibility and compute the feedback signal. For
further accuracy, the data source can use the time stamps and check
it against the RTT or the time and apply corrections.
Some processing over-head is involved if the data source has
to get in to the computation and prediction of the loss probability.
To reduce the time, shifted predicted signals may be used.
The data source receives the feedback signal and easily
shift it depending up on the delay with respect to the anticipated
time. It reduces the computation time.
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3. Security Considerations
The document concerns security of forward as well as feedback path
signals
1 The feedback signal MUST reach the source in time. Its absence could
be an indication of attack on the network.
2 An abnormal variations in the resource requirement indicated by the
feedback signal MAY be interpreted as spam or intrusion on the
network
4. IANA Considerations
This document has no actions for IANA.
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5. References
5.1 Normative References
[RFC2119] Bradner, S. "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
5.2 Informative References
[RFC2581] M.Allman, V. Paxson and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
[RFC2488] M. Allman., D. Glover, and L. Sanchez, "Enhancing
TCP over Satellite Channels using Standard Mechanisms", RFC 2488,
January 1999.
[RFC2474] K. Nichols, R., S. Blake., F. Baker and D. Black,
"Definition of the Differentiated Services Field (DS Field)
in the IPv4 and IPv6 Headers ", RFC 2474, December 1998.
[RFC3161] C. Adams, P. Cain., D. Pinkas and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)",
RFC 3161, August 2001.
[WYX01] Wei Wu, Yong Ren and Xiuming Shan, "Analysis on
adjustment-based TCP-friendly congestion control:fairness and
stability",Dept. of Electron. Eng., Tsinghua Univ., Beijing ;
In LCN 2001
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6. Author's Address
Manjunath.R
Celstream.
9,Prestige bluechip
Opp.Christ college
Bangalore-560029
INDIA
Phone: 80-41191919
E-mail: manju_r_99@yahoo.com
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7. Acknowledgements
The author acknowledges the creators of the RFCs referred in this
draft for the valuable information and the extensions based on
which this draft has been created
The following individuals directly contributed for encouragement,
identifying Issues, suggesting resolutions to the issues found in
this document: Srinivas Rao, Rangaraj. This document benefited
from all these contributions.
The author acknowledges the encouragement and services rendered
by his family members and friends during the preparation of the
document.
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8. Full Copyright Statement
Copyright (C) The Internet Society (2006). This document is
subject to the rights, licenses and restrictions contained in
BCP 78, and except as set forth therein, the authors retain
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This document and the information contained herein are
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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