draft-allman-tcp-sack-13.txt

[Erik Nordmark <Erik.Nordmark@sun.com>]

    For the purposes of this specification we define a ``duplicate
    acknowledgment'' as an acknowledgment (ACK) whose cumulative ACK
    number is equal to the current value of HighACK, as described in
    [RFC2581].
 
If somebody reads this spec without having the background of
the previous congestion control literature they might take the
above to literally and assume that all segments with ACK=HighACK
are dups, when in fact this includes data segments sent in the reverse
direction. Thus ACK=HighACK and the SEQ=RNXT (and perhaps other conditions?)
is what defines a duplicate ack.

Could be fixed with rfc-editor note once we have the text.

  Erik