[ee122] ECN and congestion

vern at cs.berkeley.edu vern at cs.berkeley.edu
Sun Dec 16 16:55:55 PST 2007

> For ECN to work (as it is described in RFC 3168), does Alice have to change
> her next outgoing packets to indicate that she understood and took measures
> to comply with ECN?

Yes.  Alice uses the new "CWR" (Congestion Window Reduced) bit in the
TCP header to signal this to Bob.

That said, you are *not* required to understand the detailed workings of
ECN, just that it provides a means by which a router can signal that a
connection should behave the same as it would have had a given packet been


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