[Cerowrt-devel] [Cerowrt-users] QOS settings vs speedboost and random bandwidth
dpreed at reed.com
dpreed at reed.com
Mon Nov 26 10:04:11 EST 2012
You can use a small fraction of the capacity of the cable uplink path to measure its queueing delay dynamically, and when it gets longer than latency*"expected bitrate", reduce "expected bitrate".
You want to do this *as quickly as possible*, so what you do is insert a "link monitor" task in the driver that sends tiny probe packets addressed to the nearest "loopback point" you can find/create on the other side, and measure the RTT. You can use, for example, the technique used by traceroute, which is to set the hop count to the smallest number that causes a return ICMP packet to be sent, and send one of those periodically.
I used this specific technique to cause my uplink queue to move back into my router, where I could manage it. You can also use it for the downlink queue measurement, but it doesn't move the queue into the router smoothly, instead you have to drop/ECN-mark the IP frames coming in.
This can all be done between the IP layer and layer 2. Since it exploits speedboost better, it might be worth adding as an option to cerowrt, so you don't have to set a speed limit explicitly when you have a single connection to the public Internet.
From: "Michael Richardson" <mcr at sandelman.ca>
Sent: Monday, November 26, 2012 9:22am
To: cerowrt-users at lists.bufferbloat.net, cerowrt-devel at lists.bufferbloat.net
Subject: Re: [Cerowrt-devel] [Cerowrt-users] QOS settings vs speedboost and random bandwidth
>>>>> "Dave" == Dave Taht <dave.taht at gmail.com> writes:
Dave> to move the fq_codel algorithm into the cable modem, OR to have the
Dave> cable modem exert flow control like ADSL modems do. Then have the
Dave> smarter device (the router) then do smarter queuing.
I was unaware that DSL models were doing this... is this with GbE
ethernet level XON/XOFF? Should I assume that any DSL model with less
than a GbE sync doesn't/can't have it? Any brands you'd like to
] He who is tired of Weird Al is tired of life! | firewalls [
] Michael Richardson, Sandelman Software Works, Ottawa, ON |net architect[
] mcr at sandelman.ottawa.on.ca http://www.sandelman.ottawa.on.ca/ |device driver[
Kyoto Plus: watch the video <http://www.youtube.com/watch?v=kzx1ycLXQSE>
then sign the petition.
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