1) dupseg_fix_=true from NS: do not count a segment with completely duplicate
data as a duplicate ack. This can occur due to duplicate packets in the
network, or due to fast retransmit from the other side.
2) dupack_reset_=false from NS: do not reset the duplicate ack counter or exit
fast recovery if we happen to get data or a window update along with a
duplicate ack.
3) In the "very old ack" case that itojun added, send an ACK before dropping
the segment, to try to update the other side's send sequence number.
4) Check the ssthresh crossover point with >= rather than >. Otherwise we
start to do "exponential" growth immediately following recovery, where we
should be doing "linear". This is what NS does.
where a keypress within the last polling interval would not be noticed.
Add a new function, conisshift(), which is used to detect whether a shift key
is pressed. Use this via awaitkey() to allow interrupting the boot by holding
down shift (similar to LILO).
This allows setting the timeout to 0 and still being able to use the boot
program.
and it could detect even older time stamps. (Really, to be 100% correct, there
should be a timer that clears these out -- but it probably doesn't matter in
the real world.)
* t_partialacks<0 means we are not in fast recovery.
* t_partialacks==0 means we are in fast recovery, but we have not received
any partial acks yet.
* t_partialacks>0 means we are in fast recovery, and we have received
partial acks.
This is used to implement 2 changes in RFC 3782:
* We keep the notion that we are in fast recovery separate from t_dupacks, so
it is not reset due to out-of-order acks. (This affects both the Reno and
NewReno cases.)
* We only reset the retransmit timer on the first partial ack -- preventing us
from possibly taking one RTO per segment once fast recovery is initiated.
As before, it is hard to measure any difference between Reno and NewReno in the
real-world cases that I've tested.
