[Make-wifi-fast] Re: [Cake] "Fi-Wi is a new forwarding plane for wireless" - Bob McMahon

[David Lang <david@lang.hm>]

bob.mcmahon@umbernetworks.com wrote:

> On dawn/usteer and 802.11r/k: these are steering protocols layered on top of 
> CSMA/CA. They help clients find a better AP but each AP still contends 
> independently for the medium. No global scheduler, no coordinated 
> transmission, no spatial stream coordination across RRHs. These systems 
> improve client placement within a distributed contention architecture. Fi-Wi 
> instead centralizes airtime scheduling itself.
>
> On what improves first and is measurable: roaming latency drops to near zero 
> because association never changes. Hidden node problems disappear because 
> there is no contention. MU-MIMO utilization becomes a scheduling decision 
> rather than a statistical outcome. Deterministic latency, which 802.11 cannot 
> guarantee by design, becomes a first-class deliverable. Those are the metrics 
> we will be publishing from real building deployments through this year.

I get the difference now, scheduling all RF transmissions across all devices 
from ne central system, that's ambitious and seems like it would hae scaling 
problems (even just the metadata is a lot of informatin to run through a single 
system with very tight timing requirements)

You speak of fiber to the room, but that doesn't seem to be the trend that I 
see. I see less interest in connections to rooms (fiber or copper), with 
'everyone will just use wifi', and reluctance to wire for the APs. I would love 
it if you had the fantastic capabilities to all the appropriate AP locations (it 
doesn't help that the 'enterprise' vendors tell them to just put in a small 
number of their multi-radio/multi-antenna/zoned APs to cover everything)

at best, you can end up controlling the AP transmissions of your APs. you can't 
control the client transmission scheduling, and you can't control other systems 
(upstairs/downstairs/adjacent neighbors, personal hotspots, etc)

the RF environment also changes depending on doors open, temporary furniture, 
room occupation, etc. You will not only need a lot of control of the 
transmitters, but you will also need a lot of receiving stations listening to 
the spectrum to hear what else is out there. This is possible with software 
defined radio receiviers, but not easy due to the very wide bandwidth that needs 
to be monitored.

On top of this, you aren't talking about one plane of RF, you have lots of them, 
one per channel, just minimizing co-channel interference by allocating the 
channels properly does wonders for performance, but is a rather hard real-world 
problem in the changing rf environment. Depending on if you can use DFS channels 
and what channel width you provide, (are you optimizing for a small number of 
high bandwidht clients, or a large number of lower bandwidth clients) the number 
of RF planes to optimize can vary. I find that lots of narrow channels re-used 
at close distances works well for conference type settings (even without 
802.11k/r). My biggest problem is clients that don't want to cooperate (apple 
being a big one)

interesting, but still a bit skeptical that this is a problem that can be 
knowable enough to try to implement a global scheduler for.

David Lang