frottle: Defeating the Wireless Hidden Node Problem

jasonjordan writes "The West Australian FreeNet Group was the first to go War Flying - and now we've released "frottle" (freenet throttle) - an open source project to control & manage traffic on fixed wireless networks. Such control eliminates the common hidden-node effect even on large scale wireless networks. frottle works by scheduling client traffic by using a master node to co-ordinate - effectively eliminating collisions! Developed and tested on the large community wireless network of WaFreeNet, We've found it has given us a significant improvement in network usability and throughput. "

Comments

Is Frottle.. is good

[Radix999]

It really does make a huge difference too. With 15 odd users on an AP we had a nightmare.. someone would start transferring a file and people would drop out, packetloss, etc. The strongest SNR would always dominate, uploads were nigh on impossible (when ANY download was occurring) and the network had no QoS at all.
Thanks to the great work of Frottle, we're now cruising along - we all get a fair go, we have QoS, and bandwidth is shared equally and we're all pretty damn pleased with it.

Is Frottle.. is good :)

Re:Is Frottle.. is good

[cybermace5]

If you had 15 normal users, would there have been a problem to begin with?

Re:Is Frottle.. is good

[Radix999]

Of course. Wireless access points generally aren't geared for large number of users OUTDOORS. The difference is that when you've got users 10-20km away collisions have a lot more effect. Individual clients don't see the traffic of other users, so it's very easy to cause collisions (this is the Hidden Node effect) - there is commercial software to solve this problem (ie. Karlnet), but the large expense and lack of Linux support (ie. use 2.4.2 kernel, Redhat 7.1 and their binary driver or else) put us off majorly.

So we rolled our own. Frottle is the result.

Wow

[BelugaParty]

before I could even understand the problem there is a solution. I'm impressed. And to think, these people do this in their spare time.

Re:802.11x topology change

[TheZombie187]

It sounds like this is an attempt to change the topology of 802.11x to a polled topology without the true benefit of such topology without changing the hardware.

Correct!

We have built a city-wide wireless freenet using commodity hardware. Things were working well, but as we grew larger the hidden node effect became a larger problem. Swapping all the hardware over is a big expense, and a big undertaking for a bunch of hobbyists.

We did investigate doing so, and also investigated a firmware solution (KarlNet TurboCell) but found it unsuitable to our needs.

On a whim, one of us implemented a small master/slave polling system in Perl which seemed to do the job surprisingly well, and it just grew from there.

Fakin' it.

[GoRK]

Well, this idea is good and all (that's why it's a part of the spec!) But the problem with a firewall-based solution is that it is behind the AP and thus the solution of traffic control through client polling is only simulated. Without the AP performing the polling, you don't acutally solve this so called "hidden node" problem.

802.11b people have a bad habit of thinking that the problems they face are new or unique, so they do a lot of re-inventing the wheel. This, normally is not a bad thing, but quite often "WiFi" supporters produce a crude solution while spewing insane amounts of bullshit radio pseudosience. When did "crosstalk" suddenly mutate into "hidden node problems?" Alvarion (Breezecom) has had polling support in their AP's for ... about 6 years or so, even the 802.11b ap's! It's like trying to make steel in your fireplace. The consumer-grade equipment is not designed to take the heat. Consumer-grade AP's are going to lack some of the features needed in carrier-grade equipment such as polling. It makes them cheaper - no doubt they are missing features.

What someone who wants to fix this really ought to do is modify the ihostap drivers to do polling 'on the air' -- If it is possible, at any rate.. I am unaware of the specific implemenation, and it's likely that even toying with the HostAP drivers will not allow one to work with the radio at a low enough level. Still, you know, if it works, it works. Traffic shaping can make things seem faster on congested networks of any kind, so if it throttles the abuser down enough where other radios can get a word in edgewise, then it does a little towards curing a symptom of the real problem. For the freenets and coffee shops, this may be entirely sufficient.

~GoRK