[tcpm] Increasing Initial CWND and CWND setting after fast recovery

[<[e-mail]>]

Hi,

RFC5681 following RFC3390 increased the initial window of TCP to 4MTU/MSS, but left the loss window after Fast Recovery
by bounded only by 2MTU from below, by formula (4) of RFC5681. I.e., ssthress = MAX (flightsize/2, 2MSS)

SCTP, from RFC2960 to RFC4960, however led the increase of the IW from 2 MTU to 4 MTU by RFC3390 impact also the loss window after Fast Recovery,
by setting ssthresh= MAX(cwnd/2, 4MTU).
(This increase may have been partly unfounded (?), nevertheless it was done with this motivation, e.g. see RFC4460)

draft-ietf-tcmp-initcwnd-08.txt mentions that the increase of the IW does NOT apply to the loss window after retransmit timeout, but
it is otherwise silent about the window after Fast Recovery. For the sake of TCP alone, but also in light of the different paths taken by TCP and SCTP
after RFC3390, then I wonder if it would not be beneficiary to clarify that the proposed increase also does NOT apply for the loss window after Fast Recovery.

If, on the contrary, the proposed increase of the windows MAY apply also to the loss window after Fast Recovery, presumably with the
disclaimer that it must not increase the CWND as it is said for the restart window, then I would very much appreciate such clarification.

I hope that you can help clarify the issue.
Thanks.

BR, Karen Nielsen