[e2e] Re: [ns]: RED treatment to SYN packet from TCP/ECN source

Sally Floyd floyd at aciri.org
Thu May 10 14:08:22 PDT 2001

The first TCP packet transmitted in a TCP connection (the SYN packet,
in the real world) has to negotiate ECN-capability between
the two end-nodes.  So the first TCP packet MUST NOT have
ECT (ECN-Capable Transport) set.  If this packet encounters
congestion, you are right, it will be dropped rather than marked
at the router.  Yes, this is unfortunate, but this is an
unavoidable coonsequence of the incremental deployment of ECN
in TCP.  This will not be the case for new transport protocols 
that include ECN from day one.

- Sally

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