Follow Slashdot blog updates by subscribing to our blog RSS feed

 


Forgot your password?
Close
typodupeerror
×
Wireless Networking The Internet Hardware

frottle: Defeating the Wireless Hidden Node Problem 121

Posted by Hemos from the wipe-it-out dept.
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. "
This discussion has been archived. No new comments can be posted.

frottle: Defeating the Wireless Hidden Node Problem More

frottle: Defeating the Wireless Hidden Node Problem

Comments Filter:

  • They're reinvented Alohanet, circa 1970 (Score:5, Informative)

    by Animats ( 122034 ) on Monday August 04, 2003 @12:50PM (#6607155) Homepage
    With the menuhene (the master node) and everything.

    Look up "slotted Aloha" [google.com] for background on this class of idea.

  • So... (Score:3, Funny)

    by Anonymous Coward on Monday August 04, 2003 @12:51PM (#6607171)
    Am I *not* supposed to understand a word of that?

  • Mirror (Score:4, Informative)

    by Anonymous Coward on Monday August 04, 2003 @12:52PM (#6607176)
    In case the site (or routes to the site) get slashdotted. Here [martin-studio.com] is a mirror. Sourceforge also has an annoying habit of downing themselves for maintenance. Enjoy!

  • Is Frottle.. is good (Score:5, Interesting)

    by Radix999 ( 28549 ) on Monday August 04, 2003 @12:53PM (#6607191)
    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 :)

  • Token ring reborn! (Score:5, Funny)

    by binaryDigit ( 557647 ) on Monday August 04, 2003 @12:54PM (#6607203)
    Fans of Madge, Thomas Conrad and IBM rejoice!

  • Speed isn't the problem... (Score:5, Funny)

    by Valar ( 167606 ) on Monday August 04, 2003 @12:59PM (#6607266)
    In a lot of cases, I have noticed, speed isn't the problem. A lot of times, I conenct to a WiFi network at full speed, and it is very responsive, and then suddenly it will drop link. It will go from full signal strength to none, seemingly instantly, then work again a minute or so later. This is because the problem is reliability of connection, especially in 'built up areas' i.e. the city. So, what we really need is a redundant, wireless backbone, so I can browse my pr0n-- err, open source software without gettting dropped signals.

  • Ah yes.... (Score:5, Funny)

    by cybermace5 ( 446439 ) <g.ryan@macetech.com> on Monday August 04, 2003 @01:01PM (#6607298) Homepage Journal
    Yet another project following the tradition of allowing the developers' children to name it.

    • agreed (Score:2, Funny)

      by jmarkantes ( 663024 )
      I agree. Freenet? Again?

      At least we know who to thank- on the bottom of frottle's page under the special thanks is:

      jas for coming up with such a catchy name

      Yay jas.... very catchy.

      J
    • Isn't a froggle a fuzzy blue frog which lives under stairs on Sesame Street?

  • Attention Project Namers: (Score:4, Insightful)

    by MyHair ( 589485 ) on Monday August 04, 2003 @01:03PM (#6607312) Journal
    Never call anything Freenet. It is too generic a term and is used for several different commercial and nonprofit organizations and projects.

    It's much worse than Firebird.

    If nothing else, realize that it messes up people who search for you on Google because of all the @freenet.com email addresses.

  • 802.11x topology change (Score:5, Informative)

    by div_2n ( 525075 ) on Monday August 04, 2003 @01:07PM (#6607343)
    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.

    In a true polled topology client packets aren't sent until the AP says they can. The client equipment remains completely silent until they receive the right to broadcast packet. AP's are programmed to completely ignore packets that are sent out of turn anyway.

    802.11x hardware is NOT designed that way. Sure you can control data flow that way but your AP is still open to the same problems as before. I wonder what happens when one of the client on one of the computers crashes and ceases to act as a polled client. Will it start hogging time slices from the AP again? Seems to me it would unless there was a radical hardware change to both AP and client adapter.

    • Re:802.11x topology change (Score:5, Informative)

      by TheZombie187 ( 208516 ) on Monday August 04, 2003 @01:17PM (#6607441)
      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.
    • I wonder what happens when one of the client on one of the computers crashes and ceases to act as a polled client.

      If people connect to the AP without frottle, essentially the collisions and packetloss appear whenever they are uploading. To discourage this, we generally firewall any non-frottle clients, using the frottle stats output in a script. Now, this doesnt stop people using the AP to repeat traffic at the MAC layer, bypassing our routed topilogy - though if this was a problem we could setup MAC fi
  • Seems like using a fork in a drillpress for a daquiri blender... doable, but rather outside the intentions of the tool designers!

    Perhaps this will stimulate some hardware vendor to make token-passing wireless network hardware to eliminate the latency problems. IBM, Madge and Thomas Conrad must have boatloads of relevant expertise already....

  • Just read the article.. (Score:1, Informative)

    by Anonymous Coward
    ..and all this is, is a glorified token ring implemented at the OS layer on top of 802.11.

    Color me unimpressed.

    • Re:Just read the article.. (Score:5, Insightful)

      by RevMike ( 632002 ) <revMike@@@gmail...com> on Monday August 04, 2003 @01:54PM (#6607761) Journal
      ..and all this is, is a glorified token ring implemented at the OS layer on top of 802.11.

      Color me unimpressed.

      Why are you critical of the solution? It appears to work well and is inexpensive. What is wrong with that?

      A friend who used to work for a "baby bell" was involved with a project to provide VoIP and video services, as well as internet, over their DSL infrastructure. The problem that they ran into was that IP, as supported by their commodity DSL equipment, did not support QoS. Their solution was to tunnel a more advanced network protocol (ATM I think) over the entire DSL IP connection. Then they ran their voice and video over ATM directly and ran IP as another tunnel over ATM. It wasn't elegant, but it was cheaper and more effective than manufacturing new devices.

      Anytime you can use commodity off-the-shelf hardware, you can usually save money.

      • This would be interesting since most DSL implementations I've seen use ATM as the transport mechanism, and then emulate/run ethernet (and subsequently IP) on top of that.

        -Brian

    • Re:Just read the article.. (Score:5, Funny)

      by Tailhook ( 98486 ) on Monday August 04, 2003 @03:25PM (#6608595)
      Color me unimpressed.

      Yeah, me too. You lamers. All you're doing is adapting old ideas that you didn't invent to new situations. You should just deal with the problem and stop trying to improve your situation. Who do you think you are? People with free will? WTF is wrong with you?

      If you want good behavior from your wireless system, you're supposed to go forth and spend large sums of money on exotic, highly vertical equipment from specialized vendors. How do you expect to command respect from anyone if you don't do it that way?

      Idiots.
    • ..and all this is, is a glorified token ring implemented at the OS layer on top of 802.11.

      And? If it works better than RTS/CTS and solves their problem..

  • Wow (Score:5, Funny)

    by BelugaParty ( 684507 ) on Monday August 04, 2003 @01:17PM (#6607439)
    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.
    • Mod this one Insightful, I say. Not for the obvious reality of its statement, but as an indicator that regular people are catching on to why the Open Way works.

  • Am I new to warring or... (Score:3, Interesting)

    by gerf ( 532474 ) on Monday August 04, 2003 @01:25PM (#6607508) Journal

    what. Is there some place that the coordinates of all these hotspots are shown? I think it would be helluva cool to be able to see GPS coordinates, or some sort of listing of where there are these hotspots around. It could be helpful in traveling, and the such.

    I don't have a wireless card, much less a laptop, but if i wanted to travel, i imagine that having something like this would be quite helpful, rather than roaming around looking for the symbol etched on a roadsign.

  • What is the state of WAFreeNet these days? (Score:3, Interesting)

    by torpor ( 458 ) <ibisum AT gmail DOT com> on Monday August 04, 2003 @01:26PM (#6607518) Homepage Journal
    I'm from Perth (born in Subiaco) and have lived outside of Australia since I was a teenager - have visited home a couple of times here and there, and every time I've been impressed with how much progress Perth has made in implementing advanced Internet technologies. Last time I was there - a year ago - I noted teams of wireless-hackers putting up repeater boxes in various neighborhoods at least 4 times - I don't know if it was just by chance, but I kept running into these 3 guys!

    One of the things which has kept me from moving back home to Perth and setting up digs has been the state of the Internet down there - the Telecom monopoly, and the distances involved, have been a big factor. Maybe I'm spoiled by American and European bandwidth situations and maybe I ought to just go home and bear with it, but I would be curious to hear from anyone who knows what the scene is like in Perth for cheap, affordable world-class Internet bandwidth?
    • ... I would be curious to hear from anyone who knows what the scene is like in Perth for cheap, affordable world-class Internet bandwidth?

      There isn't, simple. And I can't see there being for quite a long time either. I am from Perth originally (lived 18 years, now residing in Washington) and broadband in Australia is still in a very poor state, unless you are exceedingly wealthy.
    • I would be curious to hear from anyone who knows what the scene is like in Perth for cheap, affordable world-class Internet bandwidth?

      You can get some of it cheap, but it's not really world class.

      256kbit ADSL with 2GB soft cap for A$50/month
      1.5mbit ADSL with ~22GB soft cap for A$150/month
      Cable (only in some areas) with 10GB hard cap for A$300/month + A$0.10 per MB over cap

      Reliability on the ADSL is pretty crap, many of the ISP's have experienced such huge takeup that their main data pipes cant meet the

  • Fakin' it. (Score:5, Interesting)

    by GoRK ( 10018 ) on Monday August 04, 2003 @01:32PM (#6607562) Homepage Journal
    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

    • Re:Fakin' it. (Score:2, Informative)

      by m0rphm0nkey ( 616729 )
      I apprecieate your information, I was unaware that such a beast existed. However....

      Let us also consider the cost of alvarion breezecoms (the outdoor models) of easily 1600+ American dollars. I've got a choice between that and a 75 dollar (or less) AP with a 100 dollar beater laptop in a 50$ (max, maybe less if I can find something used and appropriate, which I can) hoffman box. Subtract that from the profit margin of your basic Mom&Pop Wisp (almost nonexistent labor of love style) or neghborhood
      • Well as I said in my other post in reply to my original, I did not intend to discount the frottle project in any way. I am always impressed at how proper traffic shaping can solve problems. It's very strange, isn't it, that Alvarion will charge 1000 bucks for an AP and then tell you that traffic shaping can do nothing for wireless networks! I do not necessarily like their equipment; I was just using it as an example of some that support polling.

        I also did mention that proper polling support might easily be

  • AODV (Score:1, Insightful)

    by Anonymous Coward
    I dunno, seems a bit of a kludge. Why not run the 802.11 network in ad-hoc mode and dynamic route via AODV. If there are bandwidth problems, pop in more nodes==routes. Yes, the peak performance is necessarily lower, but the worst-case performance must be much better?
    • Of course it's a kludge! But then a lot of the great things out there started as kludges like this :)

      Adhoc links are all well and good - but you try linking a large number of users via adhoc links and you'll run into a number of problems:

      Firstly, cost - that's a lot of dishes, cable and wireless cards you're talking about! We're hobbyists - not a commercial entity.

      Secondly, Line of Sight (LOS) - not everyone has LOS to everyone else. And not everyone likes putting up massive masts just so they can. Bu
  • "prevents clients with stronger signals from receiving bandwidth bias"

    all that time and effort to get a stronger signal and they're gonna cast me back down with the technon00bs?

    'screw you guys, i'm goin home'

  • This isn't the *real* hidden node problem (Score:3, Informative)

    by Anonymous Coward on Monday August 04, 2003 @02:30PM (#6608073)
    While this does deal with one aspect of the Hidden Node problem (packet collisions) you haven't fixed the real problem: The remote clients cannot hear each other. This is just a fundamental problem with CSMA/CA on a RF spectrum.

    802.11b orginially proposed using RTS/CTS to rememdy the problem, but they quickly realized that this cut network bandwidth down to 1/2 or 1/4 of available bandwidth. Not good.

    The only way that you could really fix the problem is to use multiple receivers (access points) located throughout and have them vote on the packets by using a diversity antenna pair. Between the two access points, they should get enough transmission from both stations (remote clients) to reassemble both packets and send them on their merry way.

    This software doesn't really handle 802.11b itself , which allows for clients to clobber each other. Good job getting around the problem, though.

  • Not a hidden node problem (Score:5, Informative)

    by PureFiction ( 10256 ) on Monday August 04, 2003 @02:38PM (#6608162)
    This is not really a hidden node problem, as they make it out to be.

    This is more a problem with the inherent lack of scalability of a CSMA/CA architecture. Everyone is familiar with the way ethernet degrades under saturation: you only get about 70% of that 100Mbit throughput utilized. Ethernet is CSMA/CD - collision detection.

    In wireless the problem is even more pronounced in infrastructure mode because you are using CSMA/CA -- collision avoidance. This means that for every packet to be sent, the clients must coordinate use of the medium before sending, using a RTS/CTS handshake.

    (client) can I send now?
    (AP) not your turn yet
    (client) can I send now?
    (AP) not your turn yet
    (client) can I send now?
    (AP) yes
    (client) ... data packet ...

    When you put many clients (20+) on the same AP sharing the same medium, a large amount of bandwidth is spent simply coordinating contention free access to the wireless medium itself.

    Traffic shaping (which is all frottle is doing) helps ease this problem by reducing the amount of data clients try to send/recv in a given period of time, and thus reduces some of the contention.

    This is simply a band-aid on a more fundamental problem, however.

    The only true way to prevent this kind of inefficiency for larger numbers of clients is to use a true wireless phased array switch, like vivato, which can effectively emulate a dedicated medium to each client, preventing any contention that arises in the broadcast CSMA/CA situation.

    Also, it is important to note that communication between nodes on the wireless will NOT be shaped by the frottle queues unless you are using hostap or some other linux based access point. In such a scenario, two nodes talking to each other could use as much of the medium as they liked (as coordinated by the access point itself) without frottle seeing any of the traffic.
    • Traffic shaping (which is all frottle is doing) helps ease this problem by reducing the amount of data clients try to send/recv in a given period of time, and thus reduces some of the contention.

      Not true. Each client sends its data one at time, much like a token ring.

      Yes, it's a bandaid solution, but your comments are just misleading. How about you read the documentation next time.
      • Sorry, to me this is still just a variant of traffic shaping. Push the tokens down below IP in the stack, with firmware support, and you have a token ring system.

        You may also want to try forcing the communication rates for clients operating under contention.

        iwconfig eth0 rate 11M

        This bypasses the brain dead default behavior where clients drop rates during contention. If you know you have good SQ, set it high.

        Last, any kind of ingress traffic from the clients is completely outside the control of the qu
    • No, I'm sorry, you're wrong. See my rant [slashdot.org] and specific responses below.

      In wireless the problem is even more pronounced in infrastructure mode because you are using CSMA/CA -- collision avoidance. This means that for every packet to be sent, the clients must coordinate use of the medium before sending, using a RTS/CTS handshake.

      Actually CSMA/CA does not include handling of hidden nodes. RTS/CTS was specifically ADDED to 802.11, AFTER CSMA/CA was decided, to handle the hidden node problem.

      When you put ma

      • Actually CSMA/CA does not include handling of hidden nodes. RTS/CTS was specifically ADDED to 802.11, AFTER CSMA/CA was decided, to handle the hidden node problem

        Ok, if you want to be pedantic, I was talking about CSMA/CA in the context of the 802.11 standard, which uses RTS/CTS to address the problem, just like you said. There, that's better.

        Score another point for Wi-FUD. That is ONE solution but not the ONLY solution. You could of course, also reduce contention for the shared medium by installing mu

        • Score another point for Wi-FUD. That is ONE solution but not the ONLY solution. You could of course, also reduce contention for the shared medium by installing multiple hub radios with sector antennas and save a lot of money. ... until a given sector gets overloaded. then you are back at square 1. Phased arrays are much more resilient as their beams are much, much more directed.

          Hmm.. I thought we were trying to solve the original problem. If you're going to keep piling nodes onto the hub, you're going to

  • Problems with this (Score:3, Informative)

    by Taral ( 16888 ) * on Monday August 04, 2003 @02:52PM (#6608283) Homepage
    1. Isn't this what RTS/CTS is for?

    2. What 802.11 really needs is <b>power scaling.</b> It's the big difference between cellular networks and wifi. Like the article says, the person with the highest S/N gets to talk.

    • Re:Problems with this (Score:3, Informative)

      by caseydk ( 203763 )
      RTS/CTS

      Request to Send / Clear to Send
      Required to solve (reduce) hidden station problems.

      Station 1: Hey, can I send? (RTS)
      Access Point: Yeah, go ahead. (CTS)
      Station 2 (who can't hear Station 1, but can hear the access point): Well, since a CTS came back taht I didn't request, I know someone else is sending. Therefore, I'll shut the hell up.

    • Re:Problems with this (Score:1, Interesting)

      by Anonymous Coward
      These problems are all things the product my employer [meshnetworks.com] makes solves. We do RTS/CTS, as well as power control, and full IP routing, all in hardware. RTS/CTS helps the hidden node issue, and power control allows smaller zones of interference, which gives you aggregate throughput close to the theoretical max to an access point.

      In fact, we had a similar product that did much of this in a software layer above 802.11, and measured aggregate throughputs of 2-3 times higher than vanilla 802.11. I guess that the
    • 1. Isn't this what RTS/CTS is for?

      Except that RTS/CTS doesn't work well enough.

      802.11* was designed for indoor use, so the MAC layer depends on all stations hearing each other in order to arbitrate access to the shared medium.

      As a fall-back they also included RTS/CTS mode. But RTS/CTS is rather suboptimal - some sort of polling or token mode would work better for outdoor wireless data comm.

      So these guys implemented a token mode for controlling the clients' access to the wireless medium. Hack? Sure. Wou
    • Frottle was released last week on e3, but we didnt want it getting slashdotted there.

      I only just setup the sourceforge page yesterday (though we had it registered for some time before that).

  • Frottle master is a "man in the middle" (Score:3, Interesting)

    by Ungrounded Lightning ( 62228 ) on Monday August 04, 2003 @04:51PM (#6609440) Journal
    I note that the Frottle master relays traffic when two non-master nodes wish to talk to each other - even if they could talk directly. This both reduces the potential agregate peer-to-peer bandwidth by a factor of two (or more) and sets up the Frottle master as a "man-in-the-middle".

    I'd rather see the master simply arbitrating bandwidth in its neighborhood and the peers exchanging data directly. General-casing that to multiple simultaneous masters, while relaying but only when necessary and only by efficient paths, limits out at a mesh network with extreme bandwidth usage efficiency.

    But the thing that bugs me is the security implications of having all non-master nodes relay through the master. That lets a hostile node that achieves (or spoofs-up) master-node status perform man-in-the-middle attacks on the security of the communication.

    Being man-in-the-middle is probably not a big deal if the master is also the main internet gateway (so it would be man-in-the-middle to most traffic anyhow), operated by a well-known and trusted organization. And it does simplify routing packets from one channel to another. But it bothers me anyhow.

    Fortunately, any node that can also hear its peer can check the honesty of the master's forwarding.

    Which leads to a potential way to eliminate unnecessary bounces off the master: Clients can inform it that they can hear other particular clients and what the differential delay characteristics are from their site. Then the master can just assign the transmission slot for the packet and drop it on the floor while the receiving peer captures it directly.
    • WiFI always has a man in the middle - it's called the AP. Client-Client always involves 2 radio hops. In our implementation, we've taken the step of shooting the packet over wired ethernet aswell, but it makes very little impact on performance. In fact, we found early on (before frottle) that it reduced packetloss).

      Frottle can run in many modes, and doesnt need traffic to pass through the master, though it is more reliable to do so.

      As far as Client-Client comms goes, we've always discouraged it for it'

    • Re:Frottle master is a "man in the middle" (Score:1, Informative)

      by Anonymous Coward
      I note that the Frottle master relays traffic when two non-master nodes wish to talk to each other - even if they could talk directly. This both reduces the potential agregate peer-to-peer bandwidth by a factor of two (or more) and sets up the Frottle master as a "man-in-the-middle".

      In the WAFreeNet scenario, the nodes are well dispersed, and we're all using directional antennas to connect to the APs, so the nodes cannot talk to each other directly anyway.

  • 802.11e anyone? (Score:3, Informative)

    by WoOS ( 28173 ) on Monday August 04, 2003 @05:29PM (#6609767)
    It's definitely a great hack. But of course if you just waited a year (or so ;-), 802.11e would have provided the same but with less overhead and enforcing the limits on the ether.

    11e will have a mode called HCF (Hybrid Coordinator Function) recently renamed to HCCA (forgot what that stands for) where the Accesspoint can be asked for timeslots and it will assigned them to the requestors after each beacon causing a content-free period. Only afterwards a (prioritized) contention mechanism will come into place for the rest of the transmission time till the next beacon (called EDCF=Enhanced DCF).

    Actually HCCA is not really intended for web browsing over 20km wireless link but more for real-time traffic over 10m wireless link (e.g. videos to your Webpad, PDA, ...). But it would work.
  • Iuhidden nodefS!
  • At one stage (a year go, not sure if its still the case), Perth (capital of Western Australia) had more wireless networks per capita than anywhere else in the world. Yes, that includes San Francisco.

    Why? Because it is a spread out, very flat city with piss poor and expensive broadband internet. It's also isolated from the rest of the country, so it's quite often the last Australian city to get infrastructure. There is also an abundance of unused satellite TV antennas from a failed provider, which people le
  • Have a look at Dan [bricklin.com]'s paper "Why We Don't Need QOS: Trains, Cars, and Internet Quality of Service" before you start clapping.

    I think the answer is clear: Go for more capacity rather than handling the narrow advance from dealing with congestion. That's what worked for Ethernet.


    802.11a/g are at 54 Mbps, who knows what the next jump will be.

    simon
    • <rant mode="ON">

      First, what the heck is the hidden node problem anyway? It's highly misunderstood. The hidden node problem is when you have a point to multipoint topology in your 802.11 network, aka, a "star" topology. There is one central hub that is connected to the internet, and many nodes that talk to the hub. Now this is all fine and dandy indoors, because indoors usually all of the nodes can hear not just the hub but also each other as well. So they are effectively sharing a single bus, and the
      • That's right....we'll all go spend several hundreds dollars on 802.11g equipment, that wasnt even available when we started this project. We'll find it in the fairy shop next to the magical beans, then well go spend countless hours installing it, and throw our current investments in the bin.

        Thanks, but get real.

        PS - the token in this system doesnt get passed from client to client. The master hands out a control packet, the client sends data, sends a response packet, then the master moves on.

        If the clie
        • You could double your bandwidth at the HillsHub immediately by installing another waveguide, polarized perpendicular to the current one, and on a different non-interfering channel. In australia there's 3 non-interfering channels.

          You acknowledge on your page that you are introducing greater latency. Latency is another bugbear of the 802.11 QoS crowd, because it affect voice applications. 802.11 latency also goes way up when the hidden node problem occurs. Again with that situation, increasing bandwidth will
          • The topic of buying more equipment was discussed with the HillsHub users. Unfortunately, we couldnt do it.

            As I mentioned in the story, HillsHub is very popular due to it's location. It's a private property - owned by the Uncle of one of the wireless enthusiasts. They've been gratious enough to allow one waveguide and a dish on their roof, but that's it. Even if we could put more infrastructure there, there is channel usage and other surrounding AP's (noise/interference) to be aware of. There are real

  • The story of frottle.... (Score:3, Informative)

    by aXis100 ( 690904 ) on Monday August 04, 2003 @09:29PM (#6611578)
    Once upon a time, in the mystical land of Oz, there was the quiet city of Perth. Broadband was expensive (cable was only in one suburb), and ADSL was only just beginning to roll out. WiFi has just been released, and a group of enthusiasts saw the potential.

    A bunch of people got together, and through many donations, were able to buy their first public WAFreenet Access Point. Now - Perth is fairly flat, with a long ridge running down one side - perfect! The AP was setup on a private property with an incerible view of the city, and we named it HillsHub (we'll call it HH).

    By about 5 clients, the hidden node issue started to get noticable. Easy, they turned on RTS, and it made an improvement.

    Since it had such good visibility, HH began to get pretty popular. By about 10 clients it was really stuggling, and many of those clients had AP and clients of their own adding to the routed traffic. RTS just wasnt cutting it anymore - the RTS packets are subject to collisions aswell. In a desperate effort to regain some control, rate limiting was implemented, dropping speeds back to 10kB/sec during the day to maintain some reliability. However - during the night, a free for all would occur - some people would get 100's kB/sec, whislt others would be drowned out, near complete packetloss.

    By 14 clients, the situation was ridiculous. We HAD to do something. We knew Kalrnet Turbocell (a polled system) would fix it, so we sold our soul (advertising on the e3 website) and negotiated a lower price - even then we needed to fork out A$150 each. We got together and pooled the cash, and just as we were about to buy, realised that the linux support was terrible - old, buggy kernels, binary driver only. We stopped in our tracks, and wondered what to do.

    There were plenty of ideas about building our own kalrnet, but none of us were kernel programmers, so it seemed a bit out of reach. That was until one day, when I came up with a plan. I'd read that iptables could send packets to a userspace program, so inspired by some examples (countertrace), I set about building the first version of frottle using perl.

    There was nothing new about the concept - polled systems and token rings are common knowledge in communications and networking. It wasnt difficult - it only took me a weekend, and that included the time spent learning perl (it was my first go). It was even operating at the wrong layer - using UDP control messages to schedule IP traffic. Regardless of all it's limitations, it worked, so I got the other WAFreenet members involved with testing and development. Radix picked it up and tried to continue development with C++, but had problems. Then, ChrisK took up the challege, and the result is the dynamic, performance C version we have released.

    Halfway through development, WiCCP was released. This was a similar concept, but implemented as an loadable module/interface. We liked the concept better than our userspace app, so we trialled it ourselves. One of the perth guys (Brad) even got involved with development, improving the product. Still, whislt it was an implrovement on no QoS, it didnt seem to perform quite as well as frottle. This was the decider, so ChrisK prepared frottle for release.

    So, there you have it. As a developer, I've been paying attention to the comments here. Many of you have given positive feedback, and for that we're thankfull. Unfortunately, some of you have decided it would be easier to point out the flaws...

    Well, no shit sherlock! We're quite aware of frottle's limitations, the concept is far from origonal, and it really is a kludge. The inherent problems of 802.11b are still there, and all we've done is work around them. The thing is, no-one else had done it before - at least not for free, and not when we started. We've spent our own time on frottle in order to improve our situation, and help the performance of free community wireless networks the world over.

    Criticise all you like, but the fact is, we have experienced an enourmous, measurable improvement to our network performance. As far as we're concerned, this is BIG news.

Slashdot Top Deals

It is easier to write an incorrect program than understand a correct one.

Close