[Bloat] QoS for mission critical packets on wireless networks

[Kevin Gross]

Be aware that, under some circumstances, APs intentionally hold all
multicast transmissions and transmit them on a schedule immediately
following beacon frames. This can result in multicast delivery being delayed
300 ms or more on top of buffer delays. You probably want to stick to
unicast for initial experiments to avoid potential indigestion due to this
issue.

Here's some detail -
http://www.wireless-nets.com/resources/tutorials/802.11_multicasting.html

<http://www.wireless-nets.com/resources/tutorials/802.11_multicasting.html>Kevin
Gross

On Wed, May 11, 2011 at 8:37 AM, Dave Taht <dave.taht at gmail.com> wrote:

> So...
>
> I think some *more* of the problems can be fixed by packet prioritization
> on the wireless side.
>
> So I started working on a set of wireless QoS ideas to see if I could
> improve the situation. (wilst working on red for external, wired interfaces)
>
> I started off with a hard case - a broadcast multicast protocol that runs
> over IPv6 called babel. It has the interesting property in that it sends a
> broadcast every 20 seconds from an identifiable address (theoretically - see
> the fe80 discussion also on this list) and thus I can easily (or so I
> thought) observe, with enough nodes - delays and packet loss.
>
> The idea I'm toying with now is to reserve a few percentage points of the
> bandwidth to mission critical packets such as those listed so far, using
> packet marking and a queuing discipline that does more of the "right thing"
> (hsfc or htb+sfb)
>
> (strict prioritization of things like ping would lead to trivial DDOSes on
> any of these protocols, so a tiny bandwidth reserve strikes me as a better
> approach)
>
> Wireless multicast is additionally weird in that it falls back to a very
> low rate in order to do its work.
>
> Suggestions? comments? The current build of the "capetown" release of
> bismark is very usable, has many cool features, including SFB, and supports
> several off the shelf routers commonly available via best-buy and new-egg.
>
> Anyone that's interested, please join in the effort. Certainly mere qdiscs
> are something more folk can fiddle with at a scripting and tcpdump level...
>
> Bismark documentation (supports Netgear wndr3700, wndr3700v2, nanostation
> M5, buffalo, and I just build an x86 kvm virtual machine that needs love)
>
> http://www.bufferbloat.net/projects/bismark/wiki
>
> Capetown builds:
> http://huchra.bufferbloat.net/~bismark/
>
> --
> Dave Täht
> SKYPE: davetaht
> US Tel: 1-239-829-5608
> http://the-edge.blogspot.com
>
> _______________________________________________
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> Bloat at lists.bufferbloat.net
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>
>
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