On Apr 5, 2011, at 6:07 PM, Jim Gettys wrote: > On 04/05/2011 05:59 PM, Michael Proto wrote: >> On Tue, Apr 5, 2011 at 5:38 PM, Jared Mauch<[email protected]> wrote: >>> On Apr 4, 2011, at 4:30 PM, Jim Gettys wrote: >>> >>>> Note that the paper "Characterizing Residential Broadband Networks" by >>>> Dischinger, et. al. indicates that a large fraction (in their 2 year old >>>> sample, 30% or so) of broadband head ends are running without RED, and >>>> should be doing so if at all possible; alternatives are years out by the >>>> time they are tested and deployed, and operators running without it in >>>> congested systems are inflicting pain on their customers. >>> Something I've observed is if you are sending data 'upstream' on the cable >>> modem setup i have (16 down/ 2 up) and you saturate the upstream, the >>> buffering destroys any downstream capability at the same time. I'm not >>> even sure where to start diagnosing to explaining this to the carrier >>> involved, as this isn't the desired behavior of a "business class" service. >>> >>> - Jared >>> >> Isn't this just a case or prioritizing outbound ACKs? >> >> http://www.benzedrine.cx/ackpri.html >> > > Nope. Your acks get delayed to what you are sending upstream, behind the > downstream traffic. > > Bufferbloat hurts both directions, once saturation occurs and your latencies > start to go up. > > Note that on many of these links, the RTT becomes (literally) as though you > are half way (or further than) the moon. >
I sent a private reply, but I guess i'll post some of it here: 1) there are no ways to identify the devices doing the buffering and/or drop counts 2) I can obviously feed the cable modem much faster on the lan vs what it can send upstream Doing things like rate-limiting/QoS are merely just papering over the problem. I would take a T1 and rate-limit it to 1.2Mb/s for TCP to allow VoIP to work. Junipers can buffer up to 1 second on these low-speed interfaces, which obviously creates the problems you describe. There are a lot more problems with the gateway devices, such as the forcible dns proxy that exists. - Jared
