RFC 3540:Robust Explicit Congestion Notification (...
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IP header


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... ECN-Capable Transport) is set in the ECN field of the IP header on outgoing packets. Congested routers change this field to CE ...
... CE overwrites both ECN IP header bits. Since each nonce is required to calculate the sum, ...


... out-of-order packets to be acknowledged, the nonce is recovered from the IP header. The nonce is added to the current nonce ...



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