I thought if i sent packets 11, 12, 13, and packet 11 gets dropped, then
(with no SACK) i'll time out and cut cwnd to 1, retransmit packet 11, then
get an ACK for 13 (since the receiver buffered 12 and 13), and then i'll
send 14 and 15, etc.
If true, then if some router had, for better or worse, dropped 12 and 13
as well, then i'd need another RTT before i can send 14 and 15.
neal