[Cerowrt-devel] [Cerowrt-users] QOS settings vs speedboost and random bandwidth

Michael Richardson mcr at sandelman.ca
Mon Nov 26 10:38:33 EST 2012

>>>>> "dpreed" == dpreed  <dpreed at reed.com> writes:
    dpreed> You can use a small fraction of the capacity of the cable
    dpreed> uplink path to measure its queueing delay dynamically, and
    dpreed> when it gets longer than latency*"expected bitrate", reduce
    dpreed> "expected bitrate". 
    dpreed> You want to do this *as quickly as possible*, so what you do
    dpreed> is insert a "link monitor" task in the driver that sends
    dpreed> tiny probe packets addressed to the nearest "loopback point"
    dpreed> you can find/create on the other side, and measure the RTT.
    dpreed> You can use, for example, the technique used by traceroute,
    dpreed> which is to set the hop count to the smallest number that
    dpreed> causes a return ICMP packet to be sent, and send one of
    dpreed> those periodically. 

As I understand it, you can do this with 802.1ag
with the Loop-back frames as well.

Whether or not any of this is enabled on typical broadband networks, I
have no idea.

    dpreed> I used this specific technique to cause my uplink queue to
    dpreed> move back into my router, where I could manage it.  You can
    dpreed> also use it for the downlink queue measurement, but it
    dpreed> doesn't move the queue into the router smoothly, instead you
    dpreed> have to drop/ECN-mark the IP frames coming in. 

    dpreed> This can all be done between the IP layer and layer 2.
    dpreed> Since it exploits speedboost better, it might be worth
    dpreed> adding as an option to cerowrt, so you don't have to set a
    dpreed> speed limit explicitly when you have a single connection to
    dpreed> the public Internet. 

wow, this would be awesome... code??
]       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>
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