draft-ietf-tcpm-accecn-reqs-01.txt   draft-ietf-tcpm-accecn-reqs-02.txt 
TCP Maintenance and Minor Extensions (tcpm) M. Kuehlewind, Ed. TCP Maintenance and Minor Extensions (tcpm) M. Kuehlewind, Ed.
Internet-Draft University of Stuttgart Internet-Draft University of Stuttgart
Intended status: Informational R. Scheffenegger Intended status: Informational R. Scheffenegger
Expires: January 12, 2014 NetApp, Inc. Expires: January 12, 2014 NetApp, Inc.
July 11, 2013 July 11, 2013
Problem Statement and Requirements for a More Accurate ECN Feedback Problem Statement and Requirements for a More Accurate ECN Feedback
draft-ietf-tcpm-accecn-reqs-01 draft-ietf-tcpm-accecn-reqs-02
Abstract Abstract
Explicit Congestion Notification (ECN) is an IP/TCP mechanism where Explicit Congestion Notification (ECN) is an IP/TCP mechanism where
network nodes can mark IP packets instead of dropping them to network nodes can mark IP packets instead of dropping them to
indicate congestion to the end-points. An ECN-capable receiver will indicate congestion to the end-points. An ECN-capable receiver will
feedback this information to the sender. ECN is specified for TCP in feedback this information to the sender. ECN is specified for TCP in
such a way that only one feedback signal can be transmitted per such a way that only one feedback signal can be transmitted per
Round-Trip Time (RTT). Recently, new TCP mechanisms like ConEx or Round-Trip Time (RTT). Recently, new TCP mechanisms like ConEx or
DCTCP need more accurate ECN feedback information in the case where DCTCP need more accurate ECN feedback information in the case where
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network node to cooperate honestly. network node to cooperate honestly.
Accuracy Accuracy
Classic ECN feeds back one congestion notification per RTT, Classic ECN feeds back one congestion notification per RTT,
as this is supposed to be used for TCP congestion control as this is supposed to be used for TCP congestion control
which reduces the sending rate at most once per RTT. The which reduces the sending rate at most once per RTT. The
accurate ECN feedback scheme has to ensure that if a accurate ECN feedback scheme has to ensure that if a
congestion events occurs at least one congestion notification congestion events occurs at least one congestion notification
is echoed and received per RTT as classic ECN would do. Of is echoed and received per RTT as classic ECN would do. Of
course, the goal of this extension is to reconstruct the course, the goal of this extension is to reconstruct the
number of CE marking more accurately. However, a sender number of CE markings (more) accurately and in the best case
should not assume to get the exact number of congestion even to reconstruct the (exact) number of payload bytes that
marking in all situations. a CE marked packet was carrying. However, a sender should
not assume to get the exact number of congestion markings or
marked bytes in all situations.
Complexity Complexity
Of course, the more accurate ECN feedback can also be used, Of course, the more accurate ECN feedback can also be used,
even if only one ECN feedback signal per RTT is need. The even if only one ECN feedback signal per RTT is need. The
implementation should be as simple as possible and only a implementation should be as simple as possible and only a
minimum of additional state information should be needed. minimum of additional state information should be needed.
4. Design Approaches 4. Design Approaches
All discussed approaches aim to provide accurate ECN feedback All discussed approaches aim to provide accurate ECN feedback
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