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Wireless Networks Thread, Managed Wireless Systems in Technical; The main limitation to the system is each outlet must be directly connected to the controller by CAT5 cable as ...
  1. #16

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    The main limitation to the system is each outlet must be directly connected to the controller by CAT5 cable as the outlets are effectively 'dumb' (all the work is done by the controller) the traffic to and from the outlets cannont traverse switches or media converters etc. However you can have more than one controller in a building, and these can communicate with each other over a network.

    Mike.
    Just a too big of limitation for me, this should have never been developed this way. The idea of dumb APs and controllers are fine and all the tops guys, Aruba, Trapeze, Cisco do these but the APs do have IPs and therefore do not need to connected directly to the controller. I think extricom had designed this incorrectly in my opinion.

    The wireless system should be able to be installed in most buildings, not the other way around i.e. building should not be designed to make implementing wireless networks easier. Not everyone has the luxury to have all connections terminate at a central location, so its imperative that any system put in place is flexible enough to allow implementation in various scenarios.

    Ash.

    Ash.

  2. #17

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    Quote Originally Posted by ashok View Post
    Just a too big of limitation for me, this should have never been developed this way. The idea of dumb APs and controllers are fine and all the tops guys, Aruba, Trapeze, Cisco do these but the APs do have IPs and therefore do not need to connected directly to the controller. I think extricom had designed this incorrectly in my opinion.

    The wireless system should be able to be installed in most buildings, not the other way around i.e. building should not be designed to make implementing wireless networks easier. Not everyone has the luxury to have all connections terminate at a central location, so its imperative that any system put in place is flexible enough to allow implementation in various scenarios.

    Ash.

    Ash.
    I'm sure if extricom could make their particular system work with the transmitters connected across traditional IP networks then they would, but the system works in a totally unique way, you really need a demonstration of it in order to appreciate how well it actually works.

    Personally I believe the future of enterpirse wireless systems are in a system like the extricom one. You can cover the entire building using just a single channel, no roaming problems, no interferance problems and you don't even have to be too careful about where you place the transmitters, you can put one per classroom and know they won't interfere with each other. this is totally unique even the likes of Cisco etc. still need a seperate channel for each Access Point as far as I know. The only reason extricom can get away with doing this is because the transmitters are directly connected to the controller.

    Mike.

  3. #18

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    sorry I just dont get it and agree with ashok here. Why would they design a wireless system that must be hardwired into the controller. Does that mean its limited to the 100m limit of cat5 ethernet also?! So thats the furthest away an access point can be? How does it work on a big campus if it cant traverse a switch.. Please dont say they use hubs as repeaters
    Big deal it all runs on the same channel..!? Roaming.. Well that works fine on our wlan and thats not even managed.
    If you have lots of out buildings then you need a controller in each..? Thats ridiculous. I really doubt this is the future of enterprise wireless.
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    localzuk's Avatar
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    ssiruuk2 - the system makes use of small controller units. You can buy them in sizes from 8 ports up to 24 ports I believe. An 8 port one costs a couple of grand. Not exactly expensive in my mind, when you compare it to, say, a cisco system. On a large campus, you'd install the controllers in various locations around your site, just like with your switches.

    You can't comment on this particular problem unless you've actually a) compared the price and b) seen it in action.

    Seemless roaming is not something you get easily in a managed system - you always end up with a gap. This system manages to hand your connection to the dumb AP's (which don't have an IP address, they would be more appropriately called remote antennae, this is why the system can make use of a single channel site wide, whereas the Cisco type systems can't) with no gap.

    The fact you can build it to have as many of the AP's in an area as you want makes it brilliant for schools - 30 laptops connecting to a wireless network is a horrible experience usually. What if you have 2 classrooms next door to each other using 30 each? A traditional wireless system will hit a wall. This one won't.

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    Quote Originally Posted by SYNACK View Post
    Linksys have issues with the amount of flash unless you have the linux based ones.
    Ah - just checking through a couple of websites (and those you listed, thanks) now. Seems that Linksys hardware with "L" or "S" postfixes on the model name tend to have more RAM / better hardware features. Didn't realise there was quite such an amount of replacement firmwares available. Someone must have replicated something like the Extricom system, surely?

    It's starting to look as though this is yet another situation where our school is going to win up doing all its purchasing off eBay again...

    They are also some of the worst offenders when it comes to bad PSUs
    Must be possible to get bulk replacement PSUs though, right?

    not all cards are created equal and usually an AP will have a greater maximum output power than a card.
    Thanks, I'll bear that in mind (although by the looks of it we might be looking for more individual access points rather than more powerful ones).

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    David Hicks

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    Quote Originally Posted by localzuk View Post
    Not exactly expensive in my mind, when you compare it to, say, a cisco system.
    Oh, absolutely, but there must be a way to do this for cheaper.

    they would be more appropriately called remote antennae, this is why the system can make use of a single channel site wide, whereas the Cisco type systems can't
    Is there some inherent physical reason why other managed wireless access points can't use a single site-wide channel? Or is it simply that the firmware for the access points hasn't been written to allow this? The trick seems to be accomplished by the access point figuring out that it is being interfered with by another access point and reducing its power accordingly.

    --
    David Hicks
    Last edited by dhicks; 27th July 2008 at 09:01 PM.

  7. #22

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    Taken from the Extricom FAQ;

    A common misconception in cell-based WLANs is the belief that just adding more APs and re-using the same channels will increase capacity. In practice, however, the very mechanisms of 802.11 (e.g. the Clear Channel Assessment (CCA) algorithm, rate adaptation) prevent channel re-use from providing appreciable increase in capacity, let alone bandwidth (throughput). In contrast, the channel blanket eliminates co-channel interference, the inaccuracies of CCA, and edge users stemming from rate adaptation, to ensure that the maximum throughput is delivered throughout the system, a function only of the density of APs. Simply put, in an Extricom system the more APs you add, the higher the system throughput.

    Extricom - Coverage, Capacity, and Bandwidth

    I know I sound like a sales person for these guys, but I can assure you I'm not! I was just really impressed with this product, the technology behind it, and the pratical demonstration that just worked brilliently! With developments like 802.11n wireless coming into the marketplace, the need to use as fewer channels as possible will be even greater in the future, and I think that blanket coverage systems like this will be the only way to deliver the faster standards of wireless connection on a large scale that users will demand in the not too distant future.

    Mike.

  8. #23

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    Quote Originally Posted by dhicks View Post
    Must be possible to get bulk replacement PSUs though, right?
    You should have no trouble getting different power supplies for them they use standard DC in plugs and their voltage and current needs are well documented: Supported Devices - DD-WRT Wiki

    The trick is to get good quality ones not just more of the same, the issue is that the adapters are the 'wall wart' type and so are rather imprecise about the voltages that they give out. The hardware itself is designed to handle a range of input but as it varies so much power issues can crop up when the mains supply is fluctuating. The best option is to get regulated power supplies which can offer power at +/- 1% voltage from what is on the label. If it is regulated you can also use a higher amperage rated adapter 1500 - 1700 mA without the voltage spiking because of the limited load. This will give your adapter a better chance of handling small power dips without your system becoming unstable.

    Your other option would be to offload the power requirements to a better power supply centrally using POE with a POE switch and something like these: Linksys - WAPPOE12 - 12 Volt Power Over Ethernet (PoE) Adapter Kit at CompUSA.com

    Quote Originally Posted by dhicks View Post
    Is there some inherent physical reason why other managed wireless access points can't use a single site-wide channel? Or is it simply that the firmware for the access points hasn't been written to allow this? The trick seems to be accomplished by the access point figuring out that it is being interfered with by another access point and reducing its power accordingly.
    As the other more expensive managed solutions have been unable to solve this issue in software I think that their may be more issues at play than just the wireless power. I suspect that since the controller is centralized it is able to share the wireless space more effectively by using highly precise timing and taking turns broadcasting from access points that are near each other so that each individual APs traffic does not crash into another APs broadcast. This would only be possible with a central system as IP connected wireless networks segment these tasks between APs and with the delays and uncertainties inherient in IP there would be no way to syncronize the traffic flows without slowing the system to a crawl.
    Last edited by SYNACK; 27th July 2008 at 07:33 PM.

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  10. #24

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    its actually cheaper for us to buy a cisco 4402 controller with 20 aironet thin aps than the extricom system on the basis we have 4 out buildings... And thats before you have to buy their access points. No doubt this system has its merits and does sound good from the demo but in most large secondaries with lous of buildings it seems expensive.

    I do like the idea of adding more radios to increase the throughput but how do you tell you laptops etc which ap to associate to..
    Posted via Mobile Device

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    Quote Originally Posted by SYNACK View Post
    Your other option would be to offload the power requirements to a better power supply centrally using POE
    PoE - good point, thanks for that.

    I suspect that since the controller is centralized it is able to share the wireless space more effectively by using highly precise timing... <snip> ...delays and uncertainties inherient in IP there would be no way to syncronize the traffic flows without slowing the system to a crawl.
    Damn, I reckon you're right - yes, that would explain it. It does imply that the "just keep adding access points!" idea doesn't quite work - at some point the amount of available bandwidth is going to run out, an Extricom-style system is simply making more efficient use of the available bandwidth than standard 802.11g can.

    --
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    Quote Originally Posted by ssiruuk2 View Post
    its actually cheaper for us to buy a cisco 4402 controller with 20 aironet thin aps than the extricom system on the basis we have 4 out buildings... And thats before you have to buy their access points. No doubt this system has its merits and does sound good from the demo but in most large secondaries with lous of buildings it seems expensive.

    I do like the idea of adding more radios to increase the throughput but how do you tell you laptops etc which ap to associate to..
    Posted via Mobile Device
    Yes, it is expensive you can't deny it that.

    The 'access points' aren't really access points in the extricom system, they are more elaborate 'aerials' for the controller, the controller its self is effectively the access point. To the wireless device it appears as it it's associated with the same access point anywhere you are within the building, and you are, you are associated with the controller, not the individual transmitters. The controller then simply switches transmissions to the transmitter nearest to the device which it knows because it keeps a real time track on devices within the range of each transmitter.

    If you have two transmitters close to each other, the system will load balance between them by forcing transmissions from different devices to be sent/received by a specific transmitter. The device doesn't need to associate with this transmitter, its association is with the controller so the controller can choose any transmitter it likes to send the data to the device. As long as the device is within range of the transmitter the controller has chosen, then it will receive the packets sucessfully.

    It completely and totally controls the wireless traffic within your organisation to a very precise level, I've yet to find any other wireless system that can do that to the degree that the extricom system does.

    @dhicks, yes you're right the available bandwidth will eventually run out, there's only a certain amount you can cram in any single air space, just extricom makes much better use of the available air space than most other systems can, and when you're deal with hundreds of wireless laptops in a building, that can't be a bad thing! So I agree, there is a small flaw in the keep adding Access points arguement.
    Mike.
    Last edited by maniac; 27th July 2008 at 09:37 PM.

  13. #27
    Joedetic's Avatar
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    Some copypasta on John's behalf:

    John MBCS - IT Consultant™ says:
    theres a thread made called Manged Wireless Systems so my RSS feed has told me
    John MBCS - IT Consultant™ says:
    as im not reading the form properly whilst im awy
    John MBCS - IT Consultant™ says:
    can ou post on there and say that I whole hartidly recomend ruckus
    John MBCS - IT Consultant™ says:
    got a load of kit on trial at the moment and LOVE it



  14. #28

    dhicks's Avatar
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    Quote Originally Posted by SYNACK View Post
    I suspect that since the controller is centralized it is able to share the wireless space more effectively by using highly precise timing... <snip> ...delays and uncertainties inherient in IP there would be no way to syncronize the traffic flows without slowing the system to a crawl
    Hang on, though - what about Network Time Protocol (NTP)? Checks Wikipedia... Would accuracies of 200 microseconds be good enough?

    --
    David Hicks

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    Quote Originally Posted by dhicks View Post
    How much is it costing you, for how many access points / what size of school?

    --
    David Hicks
    6k for 10x 7942 and a controller "Zone Director 1000"
    which includes all Net-Ctrl support for 3 years and hardware replacement support.

    I'm spent £800 for other network equipment for 2x 10 port gigabit PoE switchs and other networking stuff (cables, patch panels etc)

    We are a three form Primary School near the city center of Birmingham with 700 Students and staff, looking to get between 60 to 120 maybe more Mini Laptops. I'm waiting to get a loan kit of the ASUS EEE PC 1000. but so far only 70+ Workstations.

    Once you have tired the demo Kit you'll be amazed! Its makes your life easy, you wont have anything to worry about, its dead easy. if you can configure it your self which u will do, you wont have to spend like £xxx on getting someone else to configure it for you


    Hope this helps

    Steven :P

  16. #30

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    Quote Originally Posted by dhicks View Post
    Hang on, though - what about Network Time Protocol (NTP)? Checks Wikipedia... Would accuracies of 200 microseconds be good enough?

    --
    David Hicks
    Not when you are talking about a synchronized release of packets, the issue becomes your network latency rather than you accuracy unless you are just dividing up the time equally. Your average network latency will change depending on traffic levels and how much hardware is in between the controller and the AP. To schedule it efficiently the transmit/receive allowances should be real time scalable rather than fixed, otherwise you will end up with an AP with one host having the same allocated bandwidth as one with 15 hosts if they are in close proximity. One delayed or lost packet could leave the system ignoring users on one AP. There is also the traffic demands of routing every bit of signal and transmission information from each device to the controller, it would need a larger CPU just to handle all of the continuous real time information about the signals. Just putting most of the APs into full debugging mode makes them slow down to a crawl and there is far less information involved in that than the amount that would be needed to successfully imitate the extricom system.

    TCP/IP is just to unreliable and inconsistent.
    Last edited by SYNACK; 28th July 2008 at 02:27 AM.

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