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

[Matthew Toseland]

On Fri, Feb 09, 2007 at 08:03:54AM +0000, Michael Rogers wrote:
> 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.

Okay so TCP has a cooldown instead? Won't resend a given packet more
often than once per RTT?
> 
> > 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.

Indeed.
> 
> 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
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