On Tue, Apr 29, 2014 at 10:01 AM, Toke Høiland-Jørgensen <[email protected]> wrote: > Jim Gettys <[email protected]> writes: > >> Now, if someone gives me real fiber to the home, with a real switch fabric >> upstream, rather than gpon life might be somewhat better (if the switches >> aren't >> themselves overbuffered.... But so far, it isn't. > > As a data point for this, I have fibre to my apartment building and > ethernet into the apartment. I get .5 ms to my upstream gateway and > about 6 ms to Google. Still measured up to ~20 ms of bufferbloat while > running at 100 Mbps... > > http://files.toke.dk/bufferbloat/data/karlstad/cdf_comparison.png
I need to note that what this wonderfully flat CDF for the measurement stream shows is that short flows under fq_codel leap to the head of the queue ever better as you get more and more bandwidth available. The background load flows not shown on this graph are experiencing 5-20ms worth of latency in each direction as per codel's algorithm. A better test (in progress) would measure typical voip behaviors.... > However, as that graph shows, it is quite possible to completely avoid > bufferbloat by deploying the right shaping. It does not "completely avoid bufferbloat", the fq_codel "fast queue" merely eliminates queuing delay for sparse flows, things like arp, syn, syn/ack, dns, ntp, etc, as well as the first packet of any flow that has not built up a queue yet. (which is, admittedly, quite a lot of bufferbloat reduction) The rest of the magic comes from codel. > And in that case fibre > *does* have a significant latency advantage. The best latency I've seen > to the upstream gateway on DSL has been ~12 ms. And reduced RTT = money. this piece states observed average RTTs at peak times were 17ms for fiber, 28ms for cable, and 44ms for DSL. http://www.igvita.com/2012/07/19/latency-the-new-web-performance-bottleneck/ I don't know if the underlying report measures baseline unloaded last mile RTT. > > -Toke > > _______________________________________________ > aqm mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/aqm > -- Dave Täht NSFW: https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_indecent.article _______________________________________________ Cerowrt-devel mailing list [email protected] https://lists.bufferbloat.net/listinfo/cerowrt-devel
