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Wireless Networking Hardware Technology

Sluggish WiFi Connections Hurt Everyone 232

Posted by timothy from the salt-well-the-sluggish-users dept.
MindNumbingOblivion writes "Wireless technology has revolutionized access to local area networks when one can't always be close to an ethernet jack. But a recent research paper from the French Centre Nationale de la Recherche Scientifique tells how one slow user accessing a hot point can hurt the whole group. Apparently the very nature of CSMA/CD guarantees such anomalies. Here's the story, and here's the release from CNRS (in French)."
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Sluggish WiFi Connections Hurt Everyone More

Sluggish WiFi Connections Hurt Everyone

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  • Taking bets on (Score:5, Interesting)

    by groove10 ( 266295 ) on Sunday August 03, 2003 @11:17PM (#6603349) Homepage
    How long before this becomes an exploit in order to perform a DOS attack on wifi points?

    I say about 1 month, maybe less. Any takers?

    • Re:Taking bets on (Score:5, Informative)

      by That_Dan_Guy ( 589967 ) on Sunday August 03, 2003 @11:28PM (#6603406)
      There are definetly better ways to perform DOS attacks on a wireless network.

      "Wlan Jack" can send fake disassociation packets, which disconnects clients from an AP. As long as its running, nobody would be able to lock onto an access point.

      I also imagine someone could do something that would just flood noise into the spectrum that would kill the connection better than somebody just hogging it at 1 Mbps.

      • Re:Taking bets on (Score:5, Interesting)

        by child_of_mercy ( 168861 ) <johnboy AT the-riotact DOT com> on Sunday August 03, 2003 @11:45PM (#6603480) Homepage
        so, for example, i could buy a cheap(ish) handheld with wifi, get this program running on it, tape it under a table at a starbucks and deny their access point as long as the batteries held out?

        interesting,

        I really, really hate Starbucks...

        • Re:Taking bets on (Score:5, Funny)

          by 1u3hr ( 530656 ) on Sunday August 03, 2003 @11:51PM (#6603493)
          i could buy a cheap(ish) handheld with wifi... deny their access point as long as the batteries held out?

          Yeah, or you could use a pair of wirecutters and cut their phone line, with less investment ($2) and chance of being busted. Or just throw rocks through their windows.

        • I really, really hate Starbucks...

          OT, but I have to ask.

          Why? In some parts of the country it is the only place that serves decent coffee. I know several girls who went through HS and college working at Starbucks for better money than they could make elsewhere.

          • Re:Taking bets on (Score:4, Informative)

            by child_of_mercy ( 168861 ) <johnboy AT the-riotact DOT com> on Monday August 04, 2003 @01:18AM (#6603777) Homepage
            In the american context they might not be so vile,

            In the Australian context where we already have a thriving independent cafe culture, Starbucks is offering an inferior product and using marketting size and brand recognition to crush smaller players (plus wireless access).

            If their coffee was better than the alternatives I wouldn't get so riled up,

            • That makes a bit more sense. Sounds kind of like the pacific northwest portion of the US - there are tons on cool little cafes with entertainment, cool people, and good coffee. Now that I'm in a yuppie hell thousands of miles from good coffee Starbucks is as good as it gets, but when I'm in the NW I go to real coffee shops despite the Starbucks on every corner.
              • The city i live in has an ordanence against chain resturants. I live right near Seattle on an island which has a history of putting up a fight against chains. McDonalds was able to get its way in but nothing since then has been able to untill now. Starbucks is finally moving into a safeway location here after many failed attempts. The local cafe's serve much better coffee but i am afraid that Starbucks is going to steal away many customers becuase of its conveniance. I always enjoyed not seeing a Starbucks

            • Re:Taking bets on (Score:2, Insightful)

              by yomegaman ( 516565 )
              If people are going to Starbucks they must like it, they don't need your permission and they are perfectly capable of making up their own minds. Who are you to tell others what kind of coffee they should drink?
              • if not for the predatory nature of large businesses when they share space with small ones I'd agree with you completely.
                • That's one of the dark sides of capitalism... It's hard (not impossible, but hard) to have both good independent coffee shops and unchecked raw competition. In restaurants it seems work mostly (you have McDonalds and you have real restaurants), but small independent coffee shops often seem to fall just below the threshold of profitability when Starbucks et co arrive into town. I guess it might be because there's much more variety in foods than in coffees.
            • In the Australian context where we already have a thriving independent cafe culture, Starbucks is offering an inferior product and using marketting size and brand recognition to crush smaller players (plus wireless access).

              How do you know it's an inferior product? Do you even know what the product is? To me, Starbucks sells me an environment where I can study, plug in my laptop, and/or meet people for the price of a cup of coffee. To others, Starbucks means decent wages and benefits for their workers.

              • you'd prefer we lived in a value free zone where no one makes any judgments?

                go drink your swill and support the corporate goliath, I'm not stopping you.

                If there's no better alternative I suppose I'll end up there myself.

                But make your own judgments instead of being offended, not by the subtance of others judgements, but that they make them at all.
                • "you'd prefer we lived in a value free zone where no one makes any judgments?"

                  No, I prefer to live in a world where each individual makes his/her own judgement.

                  "But make your own judgments instead of being offended, not by the subtance of others judgements, but that they make them at all. "

                  I am not offended. I am just worried that some of you would be willing to take away my own individual right to chose. Not that you all think that way. If you don't, then my apologies, my message wasn't directed at

        • Yes, sometimes I understand how suicide bombers must feel, and oddly it's always when I am in a Starbucks.

    • Not likely (Score:3, Interesting)

      by ezraekman ( 650090 )
      This isn't something that's likely to become a serious exploit, for the simple reason that the attacker would need to bring a compatible device within range of the access point. Unless someone has a serious grudge against the owner of the network, who'd want to spend the time? You'd either have to be present with a laptop/pda, or leave it behind. Remember, we are talking about radio waves here. Plenty of technology [80211-planet.com] exists to track 802.11x signals, and all it takes is a well equipped sysadmin and a prope

    • Jamming (Score:4, Interesting)

      by gnarled ( 411192 ) on Monday August 04, 2003 @12:13AM (#6603578) Homepage
      Who needs sophisticated DOS attacks when simple jamming would do the trick quite well.

      • Re:Jamming (Score:2, Funny)

        by Nexzus ( 673421 )
        Mr. Sound Effects: The Access Point sir. It seems to be... jammed.

        Lord Helmet: Rasberry! There's only one man who would dare give me the rasberry! Lonestaaarrrr!.

    • Re:Taking bets on (Score:3, Insightful)

      by LostCluster ( 625375 )
      WiFi's already easy to DOS... just put a bunch of 2.4 GHz spread-spectrim phones in the neighborhood and start yakking...

  • I foresee lynchings (Score:5, Funny)

    by Faust7 ( 314817 ) on Sunday August 03, 2003 @11:18PM (#6603361) Homepage
    "What the -- we're down to 1 Mbps!"
    "There he is! Get him!"

  • Yeah but so does.... (Score:5, Funny)

    by BWJones ( 18351 ) on Sunday August 03, 2003 @11:19PM (#6603365) Homepage Journal
    Sluggish WiFi Connections Hurt Everyone

    Typing le courrier electronique or "courrier" instead of email also slows everyone down.

  • Now we just need some way to kick slow users off (Score:5, Funny)

    by Qzukk ( 229616 ) on Sunday August 03, 2003 @11:20PM (#6603370) Journal
    It could even have a message that would pop up reading:

    You are the slowest link. Goodbye!

  • I could have had first post, but nooo... (Score:5, Funny)

    by miguel_at_menino.com ( 89271 ) on Sunday August 03, 2003 @11:21PM (#6603376)

    I could have had first post, but unfortunately, another user on this hotspot has caused the network to slow down for some reason.

  • There are solutions (Score:5, Interesting)

    by That_Dan_Guy ( 589967 ) on Sunday August 03, 2003 @11:22PM (#6603377)
    If you have an 11b AP with a bunch of PCs with 11 meg cards and some kind of 2 meg hand held device then the 2 meg device is going to hog the connection until its done.

    A solution would be to leave the 802.11b AP inplace and servicing the older 2 meg devices and put an 11a or 11g AP in next to it to service the faster devices. Alternitively you might be able to put the slower devices on channel 1 and put the faster one on 6 and 11 (they have to be 5 apart to avoid overlap, and in the US you only have a total of 11 unregulated channels)

    Wireless is different than wired communication. People are just going to ahve to get used to it. More stuff to learn, more rules to follow, more work for people like me.

    Its a good thing- especially in this economy.

    • Re:There are solutions (Score:5, Interesting)

      by Anonymous Coward on Sunday August 03, 2003 @11:37PM (#6603449)
      Those with 802.11b cards that handle 11Mbps should not complain too loudly about those that connect at only 1Mbps. The 11Mbps connections slow faster wireless networks down to their speed.

      802.11g is supposed to be both 54Mbps and backwards compatible to 802.11b. From my own experience with 802.11g, if there is even one person using an 11Mbps connection, the rest of the wireless nodes also slow down.

      Just like driving on a one lane country highway behind a slow car doing only 11 mph in a 54 mph zone.

      • Re:There are solutions (Score:5, Informative)

        by heli0 ( 659560 ) on Monday August 04, 2003 @12:00AM (#6603527)
        Yep, check this out: Best Wi-Fi Ever: 802.11g [pcworld.com].

        Of three 802.11g AP's they tested, bandwidth was reduced by 15-50% for the entire wireless network when a single 802.11b card was present. It is also notable that WEP reduces bandwidth by ~30%.
      • If someone wants to support 802.11g then they could always configure an 802.11g AP so it's not dual mode and only supports "g" mode. That would keep the "b" users out. Also interms of signal strength for a larger area multiple APs can be put in place so everyone is withing a hotspot is relatively close to an access point. I'm assuming that an 802.11 client will tend to use the AP that it receives the strongest signal from.
      • Just like driving on a one lane country highway behind a slow car doing only 11 mph in a 54 mph zone.

        The speed limit must have been originally posted in metric or something

    • Anyone know if you can implement QoS and lock devices to a
      certain speed ???

      I do not know if any access points come with this feature,
      maybe the high $$$ cisco does, I have not checked .

      Peace,
      Ex-MislTech

      • Yes, You can lock devices and cards to certain speeds. HOWEVER, this will likely limit your effective coverage/range. The further away you are from the AP the more likely you have to communicate at a slower rate to maintain a high reliability delivery rate.

  • Obligatory RIAA joke (Score:5, Funny)

    by JessLeah ( 625838 ) on Sunday August 03, 2003 @11:25PM (#6603387)
    "Well, serves you right for running a wireless hot-spot. You know those things are nothing more than anonymous leeching posts for music stealers anyhow." ;)

  • WiFi doesn't use CSMA/CD (Score:5, Informative)

    by Anonymous Coward on Sunday August 03, 2003 @11:33PM (#6603424)
    Ethernet uses CSMA/CD. 802.11b uses CSMA/CA (collision avoidance). After all, not every node in a WiFi network can see or hear ther nodes, so they may not be able to detect collisions (but your receiving node might).

    Thus, each node must try to avoid causing the collision in the first place - hence such techniques as RTS/CTS protocol...
    • Sorry, my fault...I missummarized.

    • Re:WiFi doesn't use CSMA/CD (Score:5, Interesting)

      by aXis100 ( 690904 ) on Monday August 04, 2003 @12:00AM (#6603526)
      Unfortunately, RTS/CTS is almost worthless in a situation that requires it - when you've got hidden nodes, the RTS mechanism can just as easily cause collisions.

      The users of WAFreeNet (Perth, Australia) have just released some open source software (frottle) to combat this. Essentially it provides a polled/token operation at the IP layer, virtually eliminating collisions. This is a similar application to WiCCP, and we've been helping/competeing with the WiCCP developers. The other alternative is Karlnet Turbocell - expensive proprietarty software, firmware and hardware, with poor linux support.

      I cant post any url's now - the websites wouldnt appreciate the slashdotting. For those of you than can find the sites for yourself, it may be well worth your time.
      • When I first read your post I thought it was another token-ring implementation, but it looks quite a bit smarter.

        It does look fairly restricted to more or less permanent links, however, since most (preferably all) of the clients have to run the software (linux only) for it to be effective.

  • 2mbps is plenty (Score:5, Insightful)

    by vandel405 ( 609163 ) on Sunday August 03, 2003 @11:35PM (#6603442) Homepage Journal
    If your in a public location using a hotspot the only transfers your most likely going to be doing are to/from the internet, not to/from your 1337 mp3 s3v3r box. Chances are the hot spots inet connection is ~1mbps anyway.

  • nothing new (Score:3, Insightful)

    by tarzan353 ( 246515 ) on Sunday August 03, 2003 @11:36PM (#6603447)
    This is nothing new. This sort of flaw is inherent in CSMA/CD, the WiFi problem is just another example of it. Before CSMA/CD was even rolled out people knew about this situation. The pros just outweigh the cons, for what this network design philosophy is used for.

  • In other words. (Score:5, Funny)

    by Anonymous Coward on Sunday August 03, 2003 @11:39PM (#6603460)
    * LEET_POWERBOOK_1400 has joined server WIFI_POINT
    <ibm_thinkpad> omfg lag
    <LEET_POWERBOOK_1400> hi does this map have the bfg ?
    <dell_dimension> boot the lpb
    <iBook> boot leet_powerbook_1400
    * ibm_thinkpad has initiated a vote to kick LEET_POWERBOOK_1400
    * Vote to kick LEET_POWERBOOK_1400 was successful (6 for, 1 against, 1 abstain)
    * LEET_POWERBOOK_1400 has been kicked from server WIFI_POINT
    <dell_dimension> ah much better
    * dell_dimension was gibbed by iBook's rocket

  • Mainstream news, yes...slashdot, no. (Score:5, Informative)

    by petree ( 16551 ) on Sunday August 03, 2003 @11:43PM (#6603477) Journal
    For anyone who understands how these technologies work, this makes sense. It's one of the compromises that allows connectivity to happen over longer distances. As you might expect, signal degrades as you get furth away from the access point and rather than being unable from far away, it drops down to a lower speed. It just makes sense. Most people understand that wireless (802.11anything) technologies are shared bandwidth. People think "Oh it's 11mbit, that means when the access point is saturated it will be a total of 11mbit." Of course, this is only partly true. If everyone is really close and connecting at 11mbit then it will be 11mbit shared, but if everyone is connecting at 1mbit (far away) then it will 1mbit shared between everyone. This is nothing new, this is just how things work. This is why many access points have the option of only allowing 11mbit and 5mbit connections. This just seems like a bigger problem as peoples connection speeds are further apart in speed. (e.g. An 802.11g user humming along at 55mbit alone will loose approximately half his speed if a 1mbit user starts using half his bandwidth.) Don't expect to get the best of both worlds. People want a large range and high speed, it can't really happen, there are tradeoffs.

    • Re:Mainstream news, yes...slashdot, no. (Score:1, Interesting)

      by Anonymous Coward
      "People want a large range and high speed, it can't really happen"

      Go back to your cave.

      How much faster is wireless today then 5 years ago? A million percent? Do you think 802.11g is the end of wireless evolution? In ten years you don't think we will have gigabit wireless with 100m range?

      • "People want a large range and high speed, it can't really happen"

        Go back to your cave.
        How much faster is wireless today then 5 years ago? A million percent? Do you think 802.11g is the end of wireless evolution? In ten years you don't think we will have gigabit wireless with 100m range?

        I certainly don't think what we have now is the end all be all of everything, but lets be serious. Signal will always degrade the further you go away. Whether the technology lets you take advantage of this will be uncertain

    • Um this comment is a word for word rip off of one posted higher up. For moderation to work the mods have to be semi awake.

  • What? (Score:4, Informative)

    by momerath2003 ( 606823 ) on Sunday August 03, 2003 @11:46PM (#6603481) Journal

    From the yahoo article: their research paper that anomalies in the IEEE 802.1x standard -- including 802.11a, 802.11g, and the most widely-used Wi-Fi protocol, 802.11b

    I was under the impression that the IEEE 802.1x standard is solely a security standard and that it is not to be used as a generic term for the 802.11* wireless protocols. Anyone care to clear this up?

    • Re:What? (Score:4, Informative)

      by Anonymous Coward on Monday August 04, 2003 @12:02AM (#6603539)
      Typical level of journalistic polish. You are correct, 802.1x is a port based method for access control to a network. What they probably meant was 802.11x, with x as the variable (that is, until the 802.11x working group is formed ;)

  • Human translation (Score:5, Informative)

    by Kourino ( 206616 ) on Sunday August 03, 2003 @11:54PM (#6603502) Homepage
    This is why years of language study is a useful thing :D I was a bit disappointed, though, because it doesn't give much information on exactly why this happens. Guess I'll have to go see how CSMA/CA is different from CSMA/CD on my own.
    --
    A primary analysis of Wi-Fi network performance anomalies was done by four reserchers of the Institute for Information Technology and Applied Mathematics (IMAG)'s Software Systems Resources unit. Martin Heusse, Franck Rousseau, Gilles Berger-Sabbatel, and Andrzej Duda just published the surprising results of their study for the INFOCOM conference in San Francisco, on of the most prestigious in the domain of networks research. it reveals that in certain very --- circumstances, this type of wireless network produces a relatively penalizing slowdown: users with better connectivity, and thus with better data flow, are penalized by those with degraded connections.

    Local wireless networks based on the "Wi-Fi" (IEEE 802.11b) standard are starting to be deployed in a relatively large number of locations, and many models of portable computers already come with a Wi-Fi network card. Attempts providing connectivity in public places, by way of what are called "hot spots", are becoming more common. The number of potential users are increasing rapidly, and the first hot spots are in wide use, but can Wi-Fi networks stand up to the needs of numerous users and increased bandwidth demands?

    In their usual operating mode, Wi-Fi networks are built upon on a wired network infrastructure. Wireless access points rely on a local, high-bandwidth network, most commonly Ethernet, and create a link between wireless network equipment and the local wired network, as well as the internet. In practice, wireless network cards use four flow levels with different signal modulation techniques that can be selected according to the quality of the connection to the access point. More simply, a card close to an access point can get good bandwidth, nominally 11 megabits/second; as it gets farther away, the levels go to 5.5 Mbit/s, 2 Mbit/s, and finally 1 Mbit/s, as the signal gets weaker and degrades.

    As Wi-Fi networks are created, some users get the best flow (11 Mbit/s) in the access point's coverage area because they're close to the access point. A user enters in this coverage area and, being relatively far away, is connected at 1 Mbit/s. When this user communicates over wireless channels, that is, when he transmits data, it causes a drop in bandwidth for all the others, leaving them at a bandwidth apparently identical to his, 1 Mbit/s. No matter which bandwidth levels the original users are connected at, the weakest will be observed by all hosts.

    This anomaly, inherent in networks relying on CSMA/CA (Carrier Sense Multiple Access / Collision Avoidance) which is defined in the Wi-Fi standard and revealed by the CNRS research team, penalises the network users. Despite a good connection, their apparent performance can become strongly degraded in a completely unforseeable manner, due simply to the activity of a third party connected to the same wireless access point at a lower bandwidth level.

    However, though it will be observed on any network of this type, the impact of this anomaly should be more or less moderate for two reasons. First, most equipment today connects to the network in a sporadic and non-continuous manner; periods of activity, like downloading a web page, are relatively short compared to the time spent reading it. Conversly, if a long communication takes place - downloading a large video, for example - it will continuously penalize all users. A second mitigating factor comes from higher-level protocols, especially TCP, which perform some sort of flow-control that creates an effect on apparent bandwidth.

    The researchers are currently working on solutions to limit or suppress this anomaly, which could become extremely limiting with the development of new communication applications, notably audio and video over the Internet.

  • It's the nature of the system, but... (Score:4, Interesting)

    by jeffmeden ( 135043 ) on Sunday August 03, 2003 @11:58PM (#6603513) Homepage Journal
    Its good to see this sort of stuff put to paper anyway. As a Free/Open software implementer working on developing cheap-as-possible wireless access points for rural area internet distribution, I can say this IS useful. Problems like this, and many others, creep out of nowhere and are very hard to track down without expensive equipment. This specific problem happened and was remedied after much head-scratching by dividing one site into multiple cells so slow users had more 'time' to get their data. just my 0.02

    jeff
  • Configure the access point to only allow 11 mbit connections. If it's a Cisco AP, then that's relatively easy to do. I don't know about other APs.
  • Just like how one slow driver on the street causes a traffic jam that lasts hours, even on roads with many lanes. It should be allowed to beat the crap out of people like that. If you want to take your sweet time driving down the street, pull over and let the 10 billion people who actually need to get where they're going pass you, you dumb fuck.

  • slow? (Score:2)

    by MikeFM ( 12491 )
    Most users are still connecting with 56K modems and are lucky to get about a 40K connection.. so I think most could make due with 1Mbps.

  • Milwaukee has this issue (Score:5, Interesting)

    by citking ( 551907 ) * <jay AT citking DOT net> on Monday August 04, 2003 @12:32AM (#6603646) Homepage
    The Milwaukee Journal/Sentinel [jsonline.com] ran a story [jsonline.com] about becoming the 2nd US city to offer public WI-FI in two downtown parks last week. According to the article, "Randy Gschwind, the city's chief information officer... said the network serves 20 to 40 users before it becomes clogged."

    Taking into consideration that Milwaukee is a city of ~600,000 people, that not many are going to have wireless laptops and even fewer are gonna spend time in a park surfing the web, it still seems like 20-40 users clogging a public WI-FI is a bit odd.

    I suppose they can't complain, though, since the city paid less than a couple of hundred dollars for the setup. Still, it just seems somewhat pointless if it's gonna be clogged all the time.

  • Don't get excited about the obvious (Score:3, Informative)

    by mrball_cb ( 463566 ) on Monday August 04, 2003 @12:57AM (#6603710) Homepage
    For an excellent explanation of why this type of thing occurs, check out:

    http://www.karlnet.com/Documents/WhitePaper/TurboC ellWhitePaper/TurboCell%20White%20Paper.htm [karlnet.com]

    Even better is that it details a superior system (albeit pricey per node). It's based on military technology and military technology is light years ahead of what most of us are using on a daily basis.

    Blue skies...

  • Just use a phased-array wireless switch. It's easy (Score:5, Informative)

    by yancey ( 136972 ) on Monday August 04, 2003 @01:06AM (#6603740)
    The answer is to use something like the "wireless switch" that Vivato [vivato.net] developed, which uses phased-array antenna technology and can give the full 11 Mbps 802.11b bandwidth to each client.

  • Question to clarify (Score:3, Interesting)

    by timeOday ( 582209 ) on Monday August 04, 2003 @01:09AM (#6603753)
    Does this just decrease the total throughput for the base station, or does being on the same network as somebody with a slow connection actually slow you down more than if they had a fast connection?

    If I'm the only one on an 11mbps network and sitting right next to the station, I'd expect all the bandwidth. If somebody else joins the same network, in fairness my bandwidth may be halved. But do I really care whether the other guy is getting 1mbps or 11mbps during his timeslice? I'm still getting half the bandwidth as if I had it all to myself, right? I would only consider it strange if a single user joining with a weak connection cut my bandwith by > 1/n.

    • No, you're not.

      Basically, the way CSMA/CA works, when I want to transmit, I send a jamming signal. If I don't receive a jamming signal in some small amount of time, I can assume with some degree of safety that no-one else is trying to transmit at the same time. So, I go ahead and do my business, during which time no-one else can transmit.

      Now, let's say you and the other person on the network are trying to send some large file. Say your networking implementation sends a jamming signal, transmits one TCP pa
      • Interesting... though it would be much more interesting to see some benchmarks backing up the theory.

      • Re:Question to clarify (Score:5, Informative)

        by LarsG ( 31008 ) on Monday August 04, 2003 @04:43AM (#6604279) Journal
        Basically, the way CSMA/CA works, when I want to transmit, I send a jamming signal. If I don't receive a jamming signal in some small amount of time, I can assume with some degree of safety that no-one else is trying to transmit at the same time.

        Hmm? That's roughly how Ethernet works (and it's /CD and not /CA).

        With 802.11* communication, you typically transmit at ~20dBm and receive at ~-60dBm. The difference in signal strength is ~10^8, so it is pretty much impossible to detect someone else transmitting at the same time. Instead, 802.11* use Collission Avoidance. In short - listen before transmit, and explicit ACK.

        The worst case scenario will end up with simple alternation: you send a packet, the other person sends a packet; you send a packet, the other person sends a packet; etc.

        Yup. That's pretty much how the 802.11 MAC layer works if several wireless stations are trying to communicate at the same time. All stations have roughly the same chance of sending a packet, and the client @1Mbps will use 11 times more air time per packet than a client @11Mbps.

        Anyway.. I don't quite understand why you have to be a researcher to 'discover' that a client that is associated at 1Mbps can drag an entire 802.11 segment down the drain. This has been known for a long time.
    • You could have this problem, in theory, on an unswitched Ethernet network with a mixture of 10 Mbps- and 100 Mbps-capable hosts. The problem is that the bandwidth is shared, but not equally, because it just takes some users longer to transmit.
      • You could have this problem, in theory, on an unswitched Ethernet network with a mixture of 10 Mbps- and 100 Mbps-capable hosts. The problem is that the bandwidth is shared, but not equally, because it just takes some users longer to transmit.

        Kind of. Except that you can't have both 10Mbps and 100Mbps NICs connected to a hub. They all have to use the same modulation speed, so the hub is locked at either 10 or 100.

        But the theory is sound - if you have a shared medium that supports different modulation sp
  • I think it is not CSMA/CD, but is CSMA/CA instead .

    http://aqua.comptek.ru/test/HiddenNode/hidden_no de _en.html

    Thanks,
    Ex-MislTech

  • It sounds like it's time for some form of Token passing. That would prevent slow nodes from dominating the bandwidth, and would make sure everyone gets their fair share. Each node would have to register with the AP and then the AP would serve as the ring monitor.

  • Cordless Phone Attack (Score:2, Interesting)

    by Anonymous Coward
    All you need to shut down a wireless hotspot is a 2.4 GHz cordless phone. This will work for any of the 802.11X connections, lets give a hand to the FCC for this one.
    • I reccomend the Panasonic Xtreme 2.4Ghz phones. They kill WiFi connections with extreme prejudice.
    • If you would just get a ham liscense then you would have primary allocation for some of the 2.4ghz band and you could take steps to resolve the phone interference properly. I cant wait untill more hams start useing 802.11whatever and have a reason to do some 2.4ghz fox hunting. If you want more information on the Hinternet ham internet then check out www.arrl.org.

  • If I find myself in the "wet spot" I will gladly give it up to other users...

  • This is news? (Score:4, Informative)

    by Phil Karn ( 14620 ) <karn.ka9q@net> on Monday August 04, 2003 @02:25AM (#6603972) Homepage
    This is hardly an "anomaly", nor is it the fault of CSMA/CA (note: not CSMA/CD). The problem is inherent in the physics of the situation, and it's well known to radio network designers.

    The problem will occur in any shared multiple-access radio network when users are at different distances from the base station. Those far away from the base station use spectrum less efficiently than those close to the base station because they're forced to put more RF energy into each data bit to close the link.

    The same thing happens in 1xEV-DO. As in 802.11, a wide range of data rates is available to adapt to varying channel conditions, and the lower data rates use the channel less efficiently.

    Digital radio designers work hard to make their modulation, coding and multiple access techniques as efficient and adaptive as possible. But at some point, you have no alternative but to add more base stations so that each need serve only a reasonable number of users.

  • CD? (Score:3, Informative)

    by mindstrm ( 20013 ) on Monday August 04, 2003 @02:59AM (#6604054)
    I thought 802.11b and friends were not CSMA/CD but CSMA/CA. That's collision avoidance, not collision detection. CD is done electrically in ethernet.. the voltage on the line is wrong if there is a collision.. a transmitter can know immediately via feedback if it's caused a collision.

    In wireless, we don't have this... instead you re-transmit packets that get lost, and you try to avoid collisions in the first place.
  • The article is too short on technical detail to be worth anything.

    I don't think this is the Apocalypse for WiFi. The important thing to remember here that this is radio...Only one conversation can happen at a time, and the 11mbps is shared across all nodes. This is similar to a hub, but the difference is all the nodes can run at different speeds.

    The folks close to the AP will still be going 11mbps, but although the laggard out in BFE will be going 1mbps, he will not drag the others down to his level. W
  • This is a mostly manual translation of the page.

    -uso.

    First analysis of performance anomalies of Wi-Fi networks

    A first analysis of performance anomalies of Wi-Fi networks (1) was completed by four Network System Software integrators at CNRS's Institut d'Informatique et de Mathematiques Appliquees de Grenoble (IMAG). Martin Heusse, Franck Rousseau, Gilles Berger-Sabbatel, and Andrzej Duda have published the surprising results of their study, on the occasion of the INFOCOM conference in San Fransisco, on

  • Is it just me, or... (Score:4, Funny)

    by finallyHasANickname ( 559395 ) on Monday August 04, 2003 @08:01AM (#6604692) Journal
    ...are people forgetting that copper is priced per traincar load--not per troy ounce? Every time I read about 802.11x, I think, "Golly, that sounds pretty fun, but I really don't think I despise cat 5 cable that intensely anyway," and there is something about a $9 card running about 50 times faster than anyone I know could hope to afford to access the Internet sustainably, most of all knowing that everybody's operating systems can access that card about a trillion times without problems. The number after the dot that is really neat is "3". Yep. You heard it here first. 802.3 is excellent technology. That it's old is (occasionally) beside the point. BTW, I don't mean this as antagonism; I'm just literally wondering if I'm all alone here in this Luddite corner that might find copper at dirt cheap, vetted, reliable, tested, robust, negligible and "happy" 100 Mb/s to be really really really tough to beat. The next thing you know I'll be lobbying Congress to keep people using pocket calculators.

    Huh? (blush) Oh yeah. They actually are. Excuse me for the lack of controversy in my opinions. Next time I just might offend you. ;-)



  • Out of the box most access points are configured for maximum throughput. 802.11b is CSMA/CA - collission avoidance. The CA features are disabled unless you turn on maximum fragment size and some other stuff so that the clients ask the AP for permission to transmit.

    802.11 by design assumes that two transmitting clients can see each other. When remotes can't see each other, say in an outdoor access scenario, as soon as the cell gets busy you have to be all over the tuning parameters to keep the compl
  • What a simple fix. Lock your speed on the access point.

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