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Re: [ns] reworded ECN problem in NS
>Now TCP code in NS is supposed
>to reduce cwnd to 1/2 after receiving ECE Acks. My ECN flow stops after
>receiving ECE Acks. Is it due to cwnd<1 or any other problem?.
When cwnd is 1, and the CE bit is set on the packet, then
the TCP is required to wait for a retransmit timer to expire when
it receives the ACK notifying it of this ECN. TCP does not reduce
its congestion window to 1/2 in this case. The retransmit timers,
and the exponential backoff of the retransmit timers, are a
fundamental component of TCP congestion control in the highly
congested regime.
This is illustrated in Section 8 of the document
"ECN Implementations in the NS Simulator"
available from "http://www.aciri.org/floyd/ecn.html", and specified
in the ECN RFC.
- Sally
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http://www.aciri.org/floyd/
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