On Fri, 6 May 2011 14:56:01 -0700 Fred Baker <[email protected]> wrote: > > On May 6, 2011, at 8:14 AM, richard wrote: > > If every packet takes two attempts then the ratio will be 1/2 - 1 unit > > of googput for two units of throughput (at least up to the choke-point). > > This is worst-case, so the ratio is likely to be something better than > > that 3/4, 5/6, 99/100 ??? > > I have a suggestion. turn on tcpdump on your laptop. Download a web page with > lots of imagines, such as a google images web page, and then download a > humongous file. Scan through the output file for SACK messages; that will > give you the places where the receiver (you) saw losses and tried to recover > from them. > > > Putting a number to this will also help those of us trying to get ISPs > > to understand that their Usage Based Bilking (UBB) won't address the > > real problem which is hidden in this ratio. The fact is, the choke point > > for much of this is the home router/firewall - and so that 1/2 ratio > > tells me the consumer is getting hosed for a technical problem. > > I think you need to do some research there. A TCP session with 1% loss (your > ratio being 1/100) has difficulty maintaining throughput; usual TCP loss > rates are on the order of tenths to hundredths of a percent.
There is some good theoretical work which shows relationship between throughput and loss. http://www.slac.stanford.edu/comp/net/wan-mon/thru-vs-loss.html Rate <= (MSS/RTT)*(1 / sqrt{p}) where: Rate: is the TCP transfer rate or throughputd MSS: is the maximum segment size (fixed for each Internet path, typically 1460 bytes) RTT: is the round trip time (as measured by TCP) p: is the packet loss rate. It is interesting that longer RTT which can be an artifact of bloat in the queues, will hurt throughput in this case. _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
