[freenet-dev] [freenet-cvs] r11679 - in trunk/apps/load-balancing-sims/phase7/sim: . clients messages

[Michael Rogers]

Matthew Toseland wrote:
> Fast retransmission = If I get acks for 2,3,4 but not 1, then I resend
> 1, after X RTTs have elapsed?

TCP fast retransmits 1 when 2,3,4 have been acked, without considering 
the RTT. The simulator code also checks that 1 was last sent 
1.5*RTT+MAX_DELAY seconds ago, but this is just to prevent 1 from being 
retransmitted again when 5 is acked.

> Why would it be more than 4*RTT+MAX_DELAY?

Think of a probability distribution with mean m - some part of the tail 
extends beyond 4*m. The question is, does that part of the tail contain 
more than 5% of the samples? It depends on the variance.

We could change it to 10*RTT+MAX_DELAY, for example, and have a pretty 
good chance of avoiding unnecessary retransmissions - but the packets 
that were transmitted would arrive very late.

Cheers,
Michael