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Wireless Networking Hardware

Use Multiple Channels for Faster Wireless Networking 166

Posted by michael from the bandwidth-hog dept.
icypyr0 writes "The Register reports: 'Current dual-mode 802.11 'a' and 'b' access points use only one of Wi-Fi's 11 RF channels at a time, with users taking turns. The Engim chipset can 'see' all 11 at once, and can use the three non-overlapping ones (1, 6 and 11) in parallel, increasing total throughput and enabling features to be incorporated in silicon that are usually implemented, at extra cost and performance degradation, in software.'"
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Use Multiple Channels for Faster Wireless Networking More

Use Multiple Channels for Faster Wireless Networking

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  • overlap? (Score:4, Insightful)

    by StateOfTheUnion ( 762194 ) on Sunday April 11, 2004 @02:17PM (#8831470) Homepage
    Are 1,6, and 11 the only channels that don't overlap?

    • Re:overlap? (Score:5, Informative)

      by LostCluster ( 625375 ) * on Sunday April 11, 2004 @02:22PM (#8831508)
      All of the channels basically overlap with the other channels. However, if you're on 1, 6, and 11, you manage to cover the entire chart without duplicating yourself.

      Translation: They're covering the entire 2.4 GHz band, and making no appoligies to anybody else who hoped to use it near their systems. Any 2.4 GHz phones will have nowhere to hide.
      • Speaking of overlapping channels and consuming large sections of the 2.4 Ghz bandwidth, is there any Ez way to identify what other things may interfere with WiFi on a ceratain channel or channels (e.g. 2.4 Ghz cordless phone, wireless headphones, etc) or is it really just a crapshoot and one has to search for open bandwidth through trial and error?

        • Re:overlap? (Score:3, Interesting)

          by pe1rxq ( 141710 )
          Thats what you get with unregulated pieces of spectrum, everyone can put its crap on it....
          You could use a spectrum analyzer to monitor 2.4GHz band to see if anyone in your neighbourhood is using it.

          Jeroen

        • Re:overlap? (Score:3, Informative)

          by LostCluster ( 625375 ) *
          Not really. The 802.11 definiton for the channels are not used by anything else. So, if your 2.4GHz's interface claims there's 20 channels, you just have to guess if those channels are just 1/20th slices of the same pie, or if they've jumped around in their numbering scheme so that one click can get out of the footprint of most problems. You really don't know what your own devices are doing, so how can you predict what the neighbor's are throwing in?

          Trial and error it is...

          • Re:overlap? (Score:3, Informative)

            by pimpin apollo ( 664314 )

            Maybe I'm missing what you're getting at, but the 802.11b definitions for channels aren't used by anything else, but the spectrums that they cover are still unregulated... which means that anything can use it.

            Now if you're saying that you can't see those with a 802.11 aware device then yeah, but if I made some device that just broadcast randomness on the 2.4-2.5ghz range then that would interfere with all of those channels. It's also interesting to note that these ranges differ depending on the country. J

            • That's my point... that if your 2.4 GHz phone allows you to pick a channel, those channel numbers alone tell you nothing about which one to pick to get out of the way of your own WiFi, they're meaningless.
      • True, and the 2.4 GHz. phones will also stop this chipset from getting a lot more than standard Wi-Fi. Basically, it's only useful if you have a single Wi-Fi AP and no other cordless phones, APs, Bluetooth gadgets or microwave ovens within a few hundred meters.

        The best solution is to move to 5 Ghz. (802.11a), which has 13 non-overlapping channels. But this has a slightly shorter range, and chips are still slightly more expensive.

      • Re:overlap? (Score:2, Insightful)

        by tcgroat ( 666085 )
        This channel-hogging system is just as bad as using high-power amplifiers to blow other users off the channel. "My system is the only one that counts. I won't share with anybody else." It takes many times its fair share of a limited resource, ignoring a deliberate design strategy to use limited power (range) and reduced bandwidth. That design strategy exists to enable cooperative sharing of the available spectrum. The parallels to the me-first hooliganism on 27MHz Citizen's Band are frightening. Without coo

    • Re:overlap? (Score:3, Insightful)

      by pe1rxq ( 141710 )
      You could also use 2, 7 and 12 or 3, 8 and 13 as the spacing would be the same....
      If you really push it you can use smaller spacings such as three or four channels instead of six.

      Jeroen

    • Re:overlap? (Score:5, Interesting)

      by jerde ( 23294 ) on Sunday April 11, 2004 @02:34PM (#8831583) Journal
      Are 1,6, and 11 the only channels that don't overlap?

      You can get away with using four without much problem. I use 1, 4, 8, 11 for my wide-area 802.11b network.

      You have to plan out in 3 dimensions when you have multiple access points like that. Often the strongest signal available to a roaming user is above or below them, rather than on their floor.

      With only 3 channels available, it's too hard to map them out. With 4 you can at least guarantee that no two adjacent access points are on the same channel.

      - Peter

      • Re:overlap? (Score:2, Interesting)

        by PetWolverine ( 638111 )
        With 4 you can at least guarantee that no two adjacent access points are on the same channel.

        Is this a consequence of the four-color theorem? It sounds distantly related.

        • Re:overlap? (Score:3, Interesting)

          by wankledot ( 712148 )
          Yes, except with wireless there are no solid boundries, so it's not completely the same. You could have 6 non-overlapping channels are still have interfearance problems if they are stepping over each other. . It's very possible to have overlapping pieces, but as long as you manage your power levels and design it well, you should be OK.

  • More throughput... but... (Score:3, Insightful)

    by kneecarrot ( 646291 ) on Sunday April 11, 2004 @02:18PM (#8831479)
    More throughput but more pesky interference with phones and whatnot.
  • If it works for that it'd be well cool and would give speeds close to a wired network...

    Simon.

    • If it works for that it'd be well cool and would give speeds close to a wired network...

      Actually, no. A wired network provides a dedicated connection, while a wireless provides a shared one. This is basically the difference between 10baseT and 10base2. The shared connection (wireless and base2) will have to deal with collissions and will yield about 20-30% max load (depending on the kind of traffic). This is why your G network will only yield 11Mbps and not the full 54Mbps. Your 100baseT network will

      • If by dedicated you mean only the systems connected to it and not your neighbour than yes...
        However all ethernet standards 10baseT, 10base2, and also 100baseT are shared.... thats why they have things like collisions.
        You can give it the appearance of a dedicated network by using routers instead of dumb hubs.

        Jeroen
        • I think you mean a switch, not a router. A router can do this, but at a major performance cost. A switch does this by design.

          Oh, and 1000baseTX is a switched-only Ethernet(Of course, it's only really ethernet due to marketing decisions).
          • Oh, and 1000baseTX is a switched-only Ethernet(Of course, it's only really ethernet due to marketing decisions).
            Actually, it's called "ethernet" because its frame format is identical to that of the slower variants, and it supports autonegotiation to be backwards-compatible with 10Base-T and 100Base-TX.
      • Incorrect. This is only true for Switched Networks, you have bandwidth sharing on a 10baseT/100baseTX network if hubs are used network or a 10base2 network.

        However you are correct that 100baseTX will blow away 802.11g anyday even in a hub-based topology(In fact, with a properly designed network, switched full-duplex 10baseT will outperform 802.11g)

      • Re:What about 802.11G? (Score:4, Insightful)

        by timeOday ( 582209 ) on Sunday April 11, 2004 @03:21PM (#8831864)
        If I understand correctly, you're saying 10base2 is shared while 10baseT is not? That's not true. Both wire types are used for ethernet, and both are shared. Ether way, collisions aren't that big a deal after all, see the classic reference [compaq.com]:
        Ethernet works in practice, but allegedly not in theory: some people have sufficiently misunderstood the existing studies of Ethernet performance so as to create a surprisingly resilient mythology. One myth is that an Ethernet is saturated at an offered load of 37%; this is an incorrect reading of the theoretical studies, and is easily disproved in practice. This paper is an attempt to dispel such myths.

        ...

        Figure 10 shows excess delay , a direct measure of inefficiency. It is derived from the delays plotted in figure 8. The ideal time to send one packet and wait for each other host to send one packet is subtracted from the measured time. The time that remains was lost participating in collisions. Notice that it increases linearly with increasing number of hosts (offered load). When 24 hosts each send 1536-byte packets, it takes about 31 milliseconds for each host to send one packet. Theoretically it should take about 30 mSec; the other 1 mSec (about 3%) is collision overhead. Figure 4 agrees, showing a measured efficiency of about 97% for 1536-byte packets and 24 hosts.

        The upshot is that ethernet can carry very close to its rated capacity even if there are a lot of hosts and a lot of collisions. (Of course nowadays we tend to use switches instead of hubs anyhow, but that's not a at all inherent in 10baseT wiring).

        Whether wireless will work quite this well, I don't know.

  • Tragedy of the commons forming! (Score:5, Insightful)

    by LostCluster ( 625375 ) * on Sunday April 11, 2004 @02:19PM (#8831487)
    Of course, if you use the entire 2.4 GHz band, your neighbor can't. That's part of the reason why we have multiple channels to keep everybody from running into each other time. I highly doubt this group has bothered to test what kind of downside there is for a standard-issue WiFi setup operating 100 yards away.

    • Re:Tragedy of the commons forming! (Score:5, Informative)

      by MrBlue VT ( 245806 ) on Sunday April 11, 2004 @02:27PM (#8831543) Homepage
      I live right next to a university and I can see at least 15 different access points on any given day from my wireless link. I use it for internet access to the university and I can definatly tell when my neighbors are using their own LAN cause it causes a lot of packet drop outs. Not to mention about half of those APs have "linksys" as their SSID with no WEP enabled.

      It gets better during the summer when a lot of the students around me leave and shut off their APs.
    • Yes, but consider that it should be already possible (never tried it) to put multiple WiFi cards into your router and bundle the bandwidth!
      Probably, soon everyone needs such a card to shout loud enough between all the other people in your neighbourhood who have already such a thing.

      If the cards are smart enough to not completely cease to work if there is a wifi traffic jam - if they scale back on the number of channels occupied, everything should be ok(?)
    • mod up the parent. this is a big problem.

      i live in a tightly populated suburban area and i can see 8 or 10 APs immeditately around my home using simple tools like netstumbler. this doesn't count APs that don't announce their SSID, as well as who-knows-how-many 2.4ghz cordless phones.

      my 2.4ghz cordless phones get interference all the time from what i can only assume are everyone elses APs and phones around me.

      simultaneous multiple channel use is a bad idea, unless you are out-of-range of others...
    • Of course, if you use the entire 2.4 GHz band, your neighbor can't.

      Well, if you use it all the time (which is rare) then thats true with current APs.

      However, that's not necessarily true of future APs though. There's no reason why an AP can't use a directional aerial (e.g. phased array) to ignore the other APs and users, and then everyone can use the same frequencies.

      • If I understand this right, what you then could do is use a full-duplex system, when using 2 channels, one for sending, one for sending from the otherside (receiving).

        This could really speed it up when using directional equipment.

  • Overlap explained (Score:4, Informative)

    by phreak03 ( 621876 ) on Sunday April 11, 2004 @02:20PM (#8831497) Homepage Journal
    Any connection uses actually, the three channels around it for the connection anyways,
    if you've ever tried actually haveing 11 acess points on different channels you'll notice massive interfearence
    • A connection, by default, only uses one channel. However, it spills into adjacent channels because of the quality of the transmitter and the fact that the channels are fairly close together and narrow.

      • Not quite. (Score:5, Informative)

        by jvonk ( 315830 ) on Sunday April 11, 2004 @03:10PM (#8831800)
        A connection is centered on a channel. If you remember your basic signals class, the bandwidth of the connection is dependent upon the width of the signal. Therefore, the actual bandwidth (in the RF sense) consumed by a connection is dependent upon the bandwidth (in the networking sense) of the link. Nyquist theorem means that an 11 Mbps link consumes a nominal 22 MHz (11 MHz on either side of the 'center' frequency, aka. 'channel')

        You can read this [extremetech.com] for a little more info.

        • Quite not quite (Score:4, Informative)

          by rfmobile ( 531603 ) on Sunday April 11, 2004 @07:32PM (#8833625) Homepage

          Your nyquist analogy assumes a simple binary symbol set (ie. "1" and "0"). The signal bandwidth is a function of the symbol rate. If your symbol set is larger than just two symbols (say 8, or 16, or ...), then you can deliver more bits per symbol. That's why "G" delivers more data bandwidth than "B" in the confines of the same channel signal bandwidth.

          -rick
  • It seems like a fairly good idea, but also vary expensive to upgrade everyone. It seems it might be able to work if it was able to be done via a firmware upgrade though. For all major routers (Airport/Linksys/Dlink) and their fellow cards. I think the best thing todo is to make an airport card that fits the normal slot, and pccard ones from linksys/etc that are able to be upgraded by firmware, with expandable hardware. 802.11b is almost set in stone because the costs of upgrading are just too high.
    • It's pretty unlikely that a firmware upgrade could turn a single-channel radio into a multi-channel radio.
      • If you think about it the router can link to at least three cards.

        Most cards can link to at least three cards

        Use 3 connections between them and triple the throughput simple. Should work problems asociated with massive throughput aside should work well.

        My friend's network goes out when he receives a phonecall course he has a linksys router :)
    • The immediate benefit to legacy clients is that they can be partitioned into 3 channel groups, each with its own full allotment of 802.11g bandwidth.

      You would only need a hardware upgrade if you wanted each client to be able to make use of multiple channels simultaneously and reach that 50Mbps throughput figure quoted in the article.

      Otherwise it's a solution for reducing bandwidth contention in heavily trafficked networks (and protecting 802.11g users from bandwidth degradation by 802.11b clients, as ment

  • As if Wi-Fi space wasn't crowded enough already... (Score:4, Insightful)

    by misleb ( 129952 ) on Sunday April 11, 2004 @02:25PM (#8831521)
    I've been in places where you can't find a free channel because there are too many other people using Wi-Fi in the area. Now we're going to have individuals using ALL of the non-overlapping frequencies? That really sucks. As far as I am concerned, Wi-Fi as we know it will not go very far. There is just no way people are going to be able to share such a limited frequency spectrum... not in densly populated areas, anyway. I'll take good ol' reliable wires any day. Wireless is overrated.

    -matthew

  • no trimode? (Score:3, Interesting)

    by MoFoQ ( 584566 ) on Sunday April 11, 2004 @02:25PM (#8831522)
    no 'g'?

    but it's a good idea.
    Hopefully, other chipset makers (TI, etc.) follow suit, which in turn will reduce costs (thx to competition).

    Of course, if it can do all three, 'b', 'a', 'g' separately, and each with the parallel-ness, that would kick ass.
    • They're doing neither 802.11b nor 802.11g... they're violating the part of the specs that say they should only be on one channel. Therefore, their devices are compatible with both... but they're doing a flawed implementation on purpose to trade the performance gain for taking the entire 2.4GHz band as theirs.
    • The 2.4Ghz bandwidth used by 802.11b and 802.11g have overlaps. The 5Ghz used by 802.11a and upcoming 802.11h (802.11a with Power Management) have non overlapping channels.

      802.11g => ~32Mbps throughtput x 3 non-overlapping channels = ~90Mbps total usable bandwidth
      802.11a => ~25Mbps throughput x 12 non-overlapping channels = ~300Mbps total usable bandwidth
      802.11h => ~25Mbps throughput x 24 non-overlapping channels (due to better pwr mgmt) = ~600Mbps total usable bandwidth
  • They're basically getting all of their performance gains simply by violating the part of the WiFi standard that says you should only use one channel at a time, and leave 2/3 of the bandwidth space for other possible applications. Not to revolutionary a concept... just one that causes problems only for people other than the buyers of their systems.

    It's known that mixing 802.11b and 802.11g on the same network causes slowdowns... their effective solution is to put the 802.11b devices on a different channel a
  • I work with a lot of wireless APs and client cards in our lab.

    If you are talking about G type stuff, stay away from Linksys, they have the crappiest range. When I used it in my house, I would get 68db with an Intel 802.11b AP, but the Linksys G router/AP yielded 77db, and that was only going through 2 walls.

    I replaced it with a Netgear WGR614, which uses the Intersil Prism GT chipset (as does the D-Link we tested), and got much better range. Similar to straight B. ~68 or 69 db in my master bedroom.

    In our

    • Re:Some comparrisons regarding G (Score:5, Interesting)

      by bru_master ( 312436 ) on Sunday April 11, 2004 @04:46PM (#8832422)
      This is good info to have, Keep in mind if you are trying to impliment wireless in a corporate environment, crappy range is a good thing. I have common problems with Cisco and Symbol AP's having such good range that too many users will pick up the signal in the cube farms of todays corporate america.

      I try to place my AP's so that 25 users will access them from there desks or conference room. Some conference rooms that are very large I will place 2 or 3 AP's on different channels with the power turned all of the way down so it will balance the user load between the them.

      Since there are only 3 non overlaping channels it is often a chore to design wireless in a room where the same channels dont overlap with each other. Poor range solves this problem. Think of how to put 5 AP's in a room with 3 channels, it can be done, poor range is the key.

      We urge our users to use their wired connection and use their wireless when in meetings or on the road at other corporate offices.
      • I will place 2 or 3 AP's on different channels with the power turned all of the way down so it will balance the user load between the them.

        This is a great example of an intelligent use of the 802.11X protocols. Use only as much power as you need, and only where needed. As opposed to the usual (and wrong) tactic of using full-power in an attempt to squash a neighboring access point's signal.

        -rick
    • Are you refering to the Linksys client cards or the linksys wireless routers like the wrt54g?

      Are the output power the same on both of the cards/AP's you tested?

    • There are some inaccuracies I'd like to point out, if you don't mind:

      Somewhere I also read that Linksys will not support any turbo modes in their AP/Routers
      Linksys is supporting a "turbo" mode, thanks to Broadcom's "Afterburner" technology, which is implemented as Linksys's "SpeedBooster" technology. Afterburner requires a new revision of Broadcom's 802.11g chipset, however, so previous G products can't be enhanced, only new products.

      Atheros already had 108mb/s A support in turbo, allowing 45mb/sec thr

  • Interference (Score:3, Insightful)

    by Ctrl-Z ( 28806 ) <timNO@SPAMtimcoleman.com> on Sunday April 11, 2004 @02:27PM (#8831537) Homepage Journal
    This type of idea is not new, and I have seen it in wireless routers/nics for months. The primary drawback is that if you are using up all those channels, your neighbour's wireless network won't have anywhere to go. Conversely, if you are that neighbour, it wouldn't make you very happy.

    I consciously decided against buying something like this for that very reason when I bought my wireless hardware, even though the cost difference was negligible.

  • Yeah! Screw the neighbors! (Score:3, Funny)

    by Anonymous Coward on Sunday April 11, 2004 @02:27PM (#8831538)
    Take up all the channels, get a stronger transmitter, and knock their wireless out!
    • Exactly. That's the reason why the FCC and its international counterparts have to license most frequencies... otherwise there'd be more people wanting to broadcast than useful space and all sorts of jamming situations would result.

      Any time a band is released for consumer applications, this almost always happens... somebody tries an application that uses all of it. Eventually, those devices are shunned by the marketplace when they're blamed for causing everything else on the same band not to work...
    • Ha, if any of my neighbors did this, I would just be happy that my free internet was finally increasing in bandwidth and signal power.
    • It doesn't work like that. Your AP still has to recieve a singal from clients... which don't have an amplified signal.
  • The home routers that use this technology will probably have an option to limit the transmitting power (as most do right now) this will allow only the people in the house to use the connection, if the neighbor does pick up the connection, it will be so weak that the people in his house will pick up thier own signal (since it is exponentially stronger)

  • Fah. Not worth it. (Score:2, Redundant)

    by Slayk ( 691976 )
    As if setting up a wireless network in an apartment wasn't a big enough pain in the ass already, now I've got to worry about the yokel next door hogging all the available channels?

    This is going to casue more problems in resedential areas than it will solve.

  • Valid Uses (Score:3, Insightful)

    by yoshi_mon ( 172895 ) on Sunday April 11, 2004 @02:40PM (#8831622)
    While it's been duely noted that using up more channels could interfere with others who are trying to use 2.4, there are a number of applications I can see that would be useful for this type of setup.

    Large old office buildings that arn't wired for ethernet, large warehouses, and people who live on large plots of land.

    Yes, if you are living in a typical burb or in the city and try to use one of these you could run into issues with running out of channels. However not everyone lives/works in small areas.

    • Re:Valid Uses (Score:3, Interesting)

      by LostCluster ( 625375 ) *
      Large old office buildings that arn't wired for ethernet, large warehouses, and people who live on large plots of land.

      Common bond: Areas where for the range of WiFi, you control nearlly all of the territory. Therefore, you're sure you're not getting in the way of anybody else because there's nobody else arround.

      A densely packed dorm or appartment house is not the place to do that. It's to the point that in 2-family dwellings, the families need to agree on a consumer bandwidth sharing plan between each o
    • With old office buildings, I think it would still be worth wiring even if you wanted people to wander with laptops.

      The more people you have on the network, the more of an issue available bandwidth will be. Everyone getting their own dedicated 100mbps wire is better than dozens sharing 108mbps common wireless bandwidth.

      It only costed me about $100 worth of materials to connect two computers 140ft away from a switch, and a third one about 50 ft away from same switch. The cost counts metal conduit, metal b

  • Sounds like (Score:3, Insightful)

    by ajs318 ( 655362 ) <sd_resp2@earthsh ... .co.uk minus bsd> on Sunday April 11, 2004 @02:43PM (#8831644)
    This just sounds like a new form of bogarting to me. The whole idea of there ever being multiple channels in the first place was so that everybody would have a chance of finding a free one -- things like this go right against that idea.

    If it isn't actually illegal, it's certainly anti-social. But then again, I don't use any wireless kit anyway ..... I need to have a power cable, so I don't mind having a network cable as well.
    • It's not illegal by the FCC because anything goes in 2.4 GHz so long as you don't go over the power limits... there's no bandwidth-footprint limit that keeps you from using everything between the lines.

      However, this does violate the IEEE specs for 802.11b and 802.11g. They can claim that they can interoperate with such devices, but they aren't one themselves. Those specs say one channel to a customer so that other applications and networks can exist without being blown off the air.

      Two 801.11g networks nex

      • Re:Sounds like (Score:4, Interesting)

        by quantum bit ( 225091 ) on Sunday April 11, 2004 @03:06PM (#8831772) Journal
        It's not illegal by the FCC because anything goes in 2.4 GHz so long as you don't go over the power limits... there's no bandwidth-footprint limit that keeps you from using everything between the lines.

        So if my neighbors get one of these I just need something that will broadcast random noise at the maximum allowable power level over the whole 2.4Ghz band, with a directional antenna. Then we'll see how long it takes for them to give up and take it back to the store because it doesn't work.

  • Huh? (Score:2, Insightful)

    by blair1q ( 305137 )
    If I'm buying a new chipset, I'm buying 802.11g and getting 5X the speed, not just 3X.

  • What they are really talking about (Score:5, Informative)

    by ZPO ( 465615 ) on Sunday April 11, 2004 @02:49PM (#8831680)
    Based on reading the article they are talking about a software defined radio (SDR) which is capable of operating discrete carriers and user communities on each of the 3 non-overlapping channels. They are not talking about bonding all 3 channels into a single data link.

    Based on the article the chipset will be *capable* of using all 3 non-overlapping 2.4Ghz ISM channels. That will allow the associated users to be split across the 3 channels rather than all on a single channel and competing for access to the channel.

    The same tradeoffs that drive WLAN design today will still exist. Its not a panacea, but it does add new possibilities to the engineer's set of available solutions.

    By opening up the front end of the radio they can look at the whole band and do some very interesting noise reduction techniques. This is alluded to in the article, but I think its the most promising part of the chipset. The ability to identify and reduce the affects of wideband noise will got a long way to improving reception of WLAN signals....

  • tradeoff (Score:3, Interesting)

    by l33t-gu3lph1t3 ( 567059 ) <arch_angel16.hotmail@com> on Sunday April 11, 2004 @02:54PM (#8831704) Homepage
    While combining channels may be a somewhat decent idea, it has a serious drawback: you lose your usable channels! I believe that maximum feasible number of users on any one access point is about 50, right? That's on channels 1,6,11. Sure you get more speed by using just one channel and sharing the resources of all 3, but hell, now only about 17 people can use the network!
    • That depends on the access point, Cisco APs (which is what I work with at work) support hundreds and hundreds of connections.
      • I work with Cisco APs as well, in fact we just installed our wireless network. I was told by the site surveyor that 50 connections per AP was a realistic maximum given 802.11B. This seems to be contradictory to what you're telling me...so which is more accurate?

        • Re:tradeoff (Score:3, Insightful)

          by wankledot ( 712148 )
          50 is a great number to design around, because any more than that you will be cut down to a trickle of bandwidth for each one. The access points technically support quite a few more simultanous connections than that, but no one is going to suggest that you design a newwork for a thousand clients per AP. There might be some odd situation where you need more than a hundred clients per AP for some low-bandwidth use (can't think of one, maybe like, a zillion iPaqs in a big room with one AP.. who knows.

          IOW, yo

          • ah ok. We have classrooms and conference rooms that seat 170-200 and will need to support 1/2 that in wireless connections. Should be interesting then, given what you've told me.
  • ... "Use multiple camels for faster wireless networking" ??? *rolls eyes*

  • I can see the FCC loving this. (Score:3, Interesting)

    by Halvard ( 102061 ) on Sunday April 11, 2004 @02:55PM (#8831708)
    The licence that 802.11, A, B, G, etc. falls under says that if you inferfere (and you are discovered to be the culprit), you can't use it. I'm paraphrasing but I suspect that if you saturate the bandwidth available in the frequency and you get outed, then you'd have to stop using at least all the frequencies or the offending radios.

  • Dlink has a similar idea (Score:4, Interesting)

    by FigWig ( 10981 ) on Sunday April 11, 2004 @03:04PM (#8831757) Homepage
    Dlink's AirExtreme G products advertise speeds up to 108 Mbps. Their literature implies that they use two wireless channels to achieve this speed.

    I have their wireless card & router, but can't get the 108 speed because of some legacy b adapters in the network. The G speeds are quite nice - even though 802.11b's theoretical speed is higher than my DSL bandwidth, it's actual performance was quite dissapointing.

    • The G speeds are quite nice - even though 802.11b's theoretical speed is higher than my DSL bandwidth, it's actual performance was quite dissapointing.
      Heh. You know, it wasn't so long ago that pretty much nobody's LAN had more bandwidth than 10Mbit...

  • same effect using two wifi cards? (Score:3, Interesting)

    by stiller ( 451878 ) on Sunday April 11, 2004 @03:20PM (#8831859) Homepage Journal
    Maybe I'm missing something, but could you not achieve the same effect by whacking in two wifi cards and using some loadbalancing scheme in software? I don't see why this would be any slower than a hardware implemented solution, I think the CPU cycles spent are hardly the bottleneck here. Having said that, I think this is a silly solution that only wrecks the whole shared spectrum idea of wifi. If I were a wlan network admin, I would find (packet analyze) and block these guys. (not applicable on public networks ofcourse).

  • scanning networks (Score:4, Interesting)

    by Gyorg_Lavode ( 520114 ) on Sunday April 11, 2004 @03:23PM (#8831876)
    Would a card like this, integrated with airsnort and appropriate drivers allow quicker characterization of the network traffic in an area?

  • Misunderstanding of Engim (Score:5, Informative)

    by arrianus ( 740942 ) on Sunday April 11, 2004 @04:25PM (#8832266)
    What Engim is doing is actually a good bit more sophisticated than any of the Slashdot posts imply. When you transmit, you usually have two types of bandwidth: how much bandwidth you are using, and how much you are interfering with. For instance, a simple AM broadcast will require maybe 8KHz of the spectrum on which it actually transmits data. Since transmitters are imperfect, however, it may actually interfer with transmitters on, say, 20KHz of spectrum.

    As a result, if you're in a big company, and set up 3 off-the-shelf 802.11b access points, on 3 different theoretically non-overlapping bands, you'll still get something on the order of, maybe, 1.6x the bandwidth you'd get with one.

    What Engim does is it has an insanely fast ADC/DAC front-end, that grabs the entire 802.11b/g spectrum, including all the bands. Then, they have a fancy DSP that looks at the bands together, figures out how they interfere with each other, and sorts them out. As a result, in a theoretical world, where only notebooks were transmitting to the access point, they would have 3x the bandwidth. They do fancy transmitting techniques, so that notebooks on all 3 bands can hear at the same time. So if the wireless access point was transmitting, and all the notebooks receiving, they would, again, have 3x the bandwidth.

    The problem is that notebooks don't have this sort of technology, so when they transmit, they cause interference for other notebooks. If the Engim WAP transmits on band 1 to notebook A, and notebook B transmits on band 2 at the same time, the transmission from notebook B may interfere with that from the WAP. As a result, in practice, it's a little less than 3x the bandwidth, but not a heck of a lot less. They try to juggle notebooks between bands, based on location, so this doesn't happen, but it doesn't really work too well.

    The technology they have is wicked cool, actually. For those worrying about interference -- it's really not a problem. First of all, this isn't for personal WAPs, but for $1000 access points you'd see on an IBM or Microsoft campus. They won't be going in apartments any time soon. You need a minimum of 3 very expensive chips for a single WAP (RF front-end, ADC/DAC, and DSP). Those places don't tolorate employees setting up their own WAPs anyways.

    Second, you still have the remaining bands. The way 802.11 works, with the interference issues described above, if I set up a WAP, and my neighbor sets up a WAP, we will be interfering. We'll both have wireless networks, but both with reduced bandwidth. You can still set up your own WAP on any of the remaining bands, and it'll work -- it's just that if you try to send a packet at the same moment as the Engim network, you'll get a collision and retransmit. This is what happens anyways. 802.11 was never designed to have many, non-interfering bands. It was designed to have many, interfering, overlapping networks, with packet collisions. By design, the total bandwidth of 5 overlapping networks, in the same area, is the same as if there was only one. Each network gets 1/5 of the bandwidth then. This is the exact issue Engim technology is meant to address.

    In terms of cell phones, etc. my impression is that the Engim technology was actually smart enough to look for "interference sources" and try to pick bands around them. This last bit is from an Engim PowerPoint slide, so I'm not sure if it's actually implemented or vaporware.

  • Noooooooooo! (Score:4, Insightful)

    by Jahf ( 21968 ) on Sunday April 11, 2004 @04:26PM (#8832273) Journal
    This will destroy wireless ISP communities.

    I already have only -2- channels that I can reliably use in my house without interference. Every other channel is in use for ISP access in our community or gets interference from cordless phones and microwaves.

    If you want more throughput, use different frequencies. Even if they are close to 802.11b/g that is better than going into the already established spectrum.

    Yes, I know that this is not mandated or regulated space, so there is not much I can do to enforce my needs. However unregulated waves only work if people make an effort to play well together.
    • If you're getting interference from microwave ovens then it's time to call the FCC and have it stopped. A leaky microwave oven is a serious health hazard.

      I've got a scanner that receives up in the 2.4GHz range, and I've swept thru it a couple of times looking for signal while my microwave was operating - not a peep, even at 3 inches away.
  • Yeah,
    that's right now we don't have ANY spectrum left because joe smith, mary smith, and dan smith (who are all my neighbors) are using their 3 channeled access points at the same time to download music off kazaa and I'm left with no good open channels.. woohoo! great management!
  • And why use three when you can use four?

    http://www.extremetech.com/print_article/0,1583, a= 33684,00.asp

    Oh, and of course, the real world reason this isn't such a hot idea is that you can only use multiple channels to boost bandwidth only in WLAN environments where you control where the APs go so you don't have multiple APs interferring with each other.

    Steven

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