Re: 802.11p rate control

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2014-09-08 at 18:30 +0200, Rostislav Lisovy wrote:

> The possible (first implementation) solution might be either to
> implement some "dummy" rate control algorithm that will set a fixed
> datarate only once (during "ocb join" command) or to use the Minstrel
> while limiting the allowed datarate to be the lowest one; i.e.
>     mand_rates = ieee80211_mandatory_rates(sband, scan_width);
>     sta->sta.supp_rates[band] =
>         find_first_bit(&mand_rates, sizeof(u32));

That's pretty much already done anyway since you'd restrict the
supported rates to the ones that are, well, supported :)

So I don't think you need to do anything here except set up the station
correctly.


> If I am not mistaken, it is not possible to live without an in-kernel
> rate_control algorithm?
> One interesting idea I got from one colleague is to implement the
> algorithm logic in the user-space -- kernel would contain just a thin
> shell controlled from the user-space (via netlink?). This is probably
> not as insane as it may sound since the purpose of the rate-control
> algorithm for 802.11p (at least for ITS-G5) is not to "maximize the
> immediate throughput" but more like "shared medium congestion control",
> which may require much slower frequency of a control loop.

I'm not really convinced this is feasible, but in any case - are you
even communicating long enough with a single peer to make rate control
feasible?


Anyway - it seems to me that you're getting ahead of yourself. Shouldn't
you actually have a functioning datapath before worrying about rate
control? And for that you'll need station handling in mac80211, etc.

johannes