Managed Wireless Systems

[dhicks]

Hello All,

 

Managed wireless systems. I want one. How do they work? How can I make one? Specifically, what is it about a "managed" wireless solution that makes it cost £10,000 upwards, whereas just buying access points enough to cover our school would cost around £2,000? I've had a look at the websites for a couple of systems, which tend to be a little woolly on the detail side of things, but a "managed" wireless system seems to mostly consist of a central combined server/PoE switch and a bunch of access points. The access points don't generally seem to need to be plugged directly in to the server, although it seems that sales types will cheerfully try and flog you extra servers.

 

So, basically, a managed wireless solution is a server that manages a bunch of access points. Is the Sputnik system suitible for use in schools - does anyone else use this system? This system would seem to consist of just access point, managed by a central server that is an application running on top of a CentOS Linux distribution - something I could just plonk on our existing system as a VM, no need to get extra bits of hardware or anything.

 

In particular, does anyone know if the Sputnik system can handle the "high-volume" traffic that we gets in schools, i.e. 30 odd laptops in a classroom all trying to work at once? How do other systems handle this issue - do they simply reduce the power on each access point, reducing the interference between access points (but requiring more access points around the place, of course)?

 

--

David Hicks

[chilbs]

Hi

 

I would suggest having a look at an Extricom system it is a central controller with light weight access points that effectively act like radios. the system runs on one channel called a blanket. You are associated with the central controller not the individual ap so if you were to move you can move from ap to ap with out the need for the wireless devices to disassociate with one access point and then assocaite with another. if you need more through put you just add more radios and depending on what access points you get dual or quad you can run multiple types/ssids on different channels from each ap. Does not scale across fibre though so would need additional controllers for this.

 

This is being installed in some high schools that my county support.

 

rob

[stevenlong1985]

GO FOR RUCKUS WIRELESS!

 

Ruckus Wireless

 

Ruckus Wireless ZoneFlex 7942 has a Gigabit network connection (PoE) Im installing that at the moment in school, its a lot cheaper than you think.

 

 

http://net-ctrl.com/ get in contact with these lot they are the ones who helpped me out

Edited July 26, 2008 by stevenlong1985

[greatone]

The big advantage of managed systems over individual access points is that any changes are only done once on the central controller and not on each access point. All the access points get their configuration from the controller.

 

I must agree with stevenlong1985

 

We also went with net-ctrl. Two guys came in, one sales and one tech, gave us the spiel and a demo then left the kit with us to play with. It gave us the chance to carry out some basic range and capacity checks and to see how difficult it was to set up. The answers were great, great and easy!

 

We were so impressed that we bought a controller and 16 access points which, like stevenlong1985, we are currently installing.

[dhicks]

if you need more through put you just add more radios

 

If all the access points are on the same channel, how does the central controller avoid the access points interfering with each other?

 

Does not scale across fibre though

 

Why not?

 

--

David Hicks

[ssiruuk2]

with a system like that above do you still need an external radius server and CA or does the controller deal with that also?

Posted via Mobile Device

[dhicks]

Ruckus Wireless , its a lot cheaper than you think.

 

How much is it costing you, for how many access points / what size of school?

 

--

David Hicks

[dhicks]

All the access points get their configuration from the controller.

 

Has anyone used the Sputnik system? This seems to work by replacing the supplied firmware on the router with their own OS that then works with their own management server, thus, it would seem, you can do the centrally-managed part of things (central configuration) for the cost of some access points rather than having to buy a whole specialised bit of hardware.

 

Thanks to everyone for your replies, but I'm really not asking for recommendations as to systems or which-reseller-is-best, that's just shopping - I want to know what a "managed wireless system" actually does, how one works. Having read through the information available on a couple of websites (the Extricom one included), I get the sneaky suspicion that the answer is "not much" or "nothing you can't do yourself". Most of the "information" available tends to be of the sales-waffle type, I want some more detailed information here if anyone has it.

 

--

David Hicks

[maniac]

If all the access points are on the same channel, how does the central controller avoid the access points interfering with each other?

 

--

David Hicks

 

With the Extricom system, the whole building is effectively covered by one access point with multiple outlets, the controller intelligently increases or decreses the power of each outlet to create a blanket coverage. You can flood your building with as many of these outlets as you like, and the system will simply work everything out else out for you.

 

One advantage of this is you can run 3 seperate wireless networks within your school, on channels 1, 4 and 12 so you can have seperate wireless networks for Students, Staff and wireless VOIP services which in turn can be routed to different V-LANs etc. You can also be sure you will suffer no interference from access points using different channels like you may get with traditional wireless systems. It also means roaming problems become a thing of the past because to the device it appears as if its connected to the same access point no matter where you are in the building, the controller intelligently routes the traffic to the nearest outlet to the laptop, and handles all the switching of traffic as you move around the building.

 

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.

 

If I were building a new build, I would definitely consider this system as the building could be wired for it easily. If I was fitting in an existing building a lot would depend on the ease of being able to run each cable back to a central location. If that was a problem, then a 'traditional' managed wireless system might suit your needs better.

 

Mike.

Edited July 26, 2008 by maniac

[dhicks]

the controller intelligently increases or decreses the power of each outlet to create a blanket coverage.

 

I figured it might use this method - so the controller adjusts the power of each access point to create isolated "pools" of wireless coverage that don't interfere. Makes sense, but doesn't that mean that if a user is stood right in the middle of two "pools" they won't get a signal - won't there be gaps in the network?

 

Seemingly Sputnik's custom access point firmware can also accomplish this power-adjustment trick - 0-251mW, their website reckons ("default is 28mW, 100mW is safe"). I don't know if their controller system can auto-adjust power settings as it senses interference between access points, but I figure even if we have to wander around for a day testing coverage it'll be worth it to save £8,000.

 

the system will simply work everything out else out for you.

 

Any details on how, exactly, this working out is done?

 

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'

 

The resellers I spoke to on Friday seemed to think that I could place individual access points with PoE injectors, the controller could be in a separate building. Said resellers could simply (actually, quite likely) be wrong, of course.

 

--

David Hicks

[maniac]

I figured it might use this method - so the controller adjusts the power of each access point to create isolated "pools" of wireless coverage that don't interfere. Makes sense, but doesn't that mean that if a user is stood right in the middle of two "pools" they won't get a signal - won't there be gaps in the network?

 

Because they are all controlled centrally, the unit can work out which transmitters are near each other, how far apart they are positioned and vary the signal strengths to ensure there are no gaps in coverage. If you think of the transmitters a merely 'arials' for a big access point (the controller) then it makes a little more sense. The coverage from each transmitter is allowed to overlap, the controller is clever and chooses in realtime which transmitter to use for a particular device. The laptops wireless adapter doesn't have to associate and deassociate with access points unless you move between different controllers

 

The company I contacted did a brillient demo for us. Because the extricom sortware has the capability to show you what transmitter a device is talking to in real time, they had 3 connected to a controller and couple of VOIP handsets. Me and my network manager roamed around the room talking to each other and you could see the software changing the transmitter that each phone was talking to quite frequently according to which one was closest (They were all within 5 metres of each other as it was!) there was zero dropout on the conversation while we walked around. I was impressed needless to say.

 

We didn't buy it unfortunitely as it was quite pricey (including installation) for our building because it was a large school on 3 floors with 3 different buildings to cover, meaning we'd need more controllers than normal, the controllers are what add cost to the system.

 

 

The resellers I spoke to on Friday seemed to think that I could place individual access points with PoE injectors, the controller could be in a separate building. Said resellers could simply (actually, quite likely) be wrong, of course.

 

--

David Hicks

 

The communication between transmitter and controller on the extricom system definitely can't traverse switches, I specifically asked this question and was told no. They explained why as well. Each transmitter has to be Directly connected as the communcation between the transmitters and the controller is not done using a 'traditional' IP system, they are dumb, don't have an IP address or simelar and effectively 'talk' in their own language back to the extricom controller. The only bit with an IP address talking on your actual network is the controller itself.

 

On a more 'traditional' managed wireless system, the access points are still intelligent in their own right, and generally have an IP number each and could (in theory) be administered seperately. They can be connected into whatever switch you like on your network as they all talk to each other and the rest of the network in normal IP packets. The controller unit with these just 'oversees' the wireless network, sends and retrieves information from them all and monitors them so you have a central point to control them and get information from.

 

I would get a demonstration of the extricom system if you can, as it's a pretty unique type of wireless network as far as I know and I expect their sales or technical people could do a much better job of explaining it! I was certainly impressed as you can tell!

 

Having read through the information available on a couple of websites (the Extricom one included), I get the sneaky suspicion that the answer is "not much" or "nothing you can't do yourself".

 

With a more 'traditional'type of wireless system I would agree, but that's why I was so impressed with the Extricom system, as it is doing something totally different and unique and solves easily a fair few problems you can get with a traditional wireless system. It also works well and can be seen to work, that's why I was so instantly impressed with it, and why I don't mind raving about it on here!

 

Mike.

Edited July 26, 2008 by maniac

[dhicks]

The coverage from each transmitter is allowed to overlap

 

If coverage overlaps, how come you don't get problems from interference?

 

The company I contacted did a brillient demo for us.

 

Your description sounds suitably impressive, although it's still rather pricey for us (we'd need several separate controllers too). I see there's currently some kind of offer on with different resellers for the Extricom "starter" kit - a controller with four access points for somewhere under £3,000-ish. We could probably use that just for our prep school - aiming for sections of the school to be covered rather than blanket coverage might be affordable.

 

Each transmitter has to be Directly connected

 

Makes sense - I think I'll avoid the reseller I spoke to on Friday in the future if they can't explain stuff clearly. Defiantly going to have to check out this Sputnik system, too.

 

--

David Hicks

[SYNACK]

One core difference with a managed wireless system is the quality of the hardware involved. Lots of the standard APs and routers that you can buy come with an extremely limited amount of RAM and CPU speed. They often also have really rubbish power supplies which when put together are some of the main reasons that they are flaky even in a home environment.

 

If a standard AP bogs down under the load of a single bittorrent connection due to insufficient memory to deal with that many connections at once it is likely to pull the same tricks when confronted with 10 to 15 clients no matter what software it is running.

 

A manages wireless system may have APs that include two or more seporate radios enabeling them to run on multiple channels simultaniously and divide the clients up between them. The managed variety will oftern have radios that are more adjustable when it comes to power level enabling them to use output powers all the way up to the legal maximum.

 

Other features are also avalible in some devices like the ability to automatically search for rogue wireless APs that are not in your network and suppress them by broadcasting on the same channels.

 

You can do a lot with standard APs and I will probably have a look at that software that you meantioned as it sounds quite interesting. Overall I would liken it to the difference between server grade stuff and workstation grade stuff. Standard APs may be able to do most of the stuff but you do not get the same level of quality hardware wise so the reliability and overall speed are compromised without large levels of redundancy and extra tools in place.

[dhicks]

Lots of the standard APs and routers that you can buy come with an extremely limited amount of RAM and CPU speed.

 

The Spunik website seems keen on the Linksys brand, which is handy as that's what we have. We could, of course, buy new access points from them, or buy the components to make our own.

 

Can an "access point" simply be a PC with a wireless card in? Is there any fundamental difference in hardware between a PC's wireless PCI card and that in an access point?

 

--

David Hicks

[SYNACK]

The Spunik website seems keen on the Linksys brand, which is handy as that's what we have. We could, of course, buy new access points from them, or buy the components to make our own.

 

Can an "access point" simply be a PC with a wireless card in? Is there any fundamental difference in hardware between a PC's wireless PCI card and that in an access point?

 

--

David Hicks

 

Linksys have issues with the amount of flash unless you have the linux based ones. They are also some of the worst offenders when it comes to bad PSUs, as proved at my house mere hours ago. Had a small power fluctuation and only two devices fell over, the 20 year old microwave and the 1 year old Linksys wireles router. A better made power supply brick would solve that issue though, it won't however solve the more limited RAM issue.

 

You can switch a computer adapter to AP mode but it is dependant on the drivers. Back when wireless was new this was quite a common practice to build APs that would standup to a lot of traffic without spending vast amounts on a business grade one. It also depends on the radio power of the cards in question as not all cards are created equal and usually an AP will have a greater maximum output power than a card.

 

To better replicate a propper managed ap you would probably be wanting to look at stocking your PCs with a couple of high power wireless cards and a nice cut down version of linux to handle all of the routing and managment overhead of the wireless networks.

 

http://oob.freeshell.org/nzwireless/LWAP-HOWTO.html

http://www.ibm.com/developerworks/library/l-wap.html

http://www.linux.com/articles/55617

Edited July 27, 2008 by SYNACK

[spc-rocket]

 

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.

[maniac]

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.

[ssiruuk2]

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.

Posted via Mobile Device

[localzuk]

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.

[dhicks]

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).

 

--

David Hicks

[dhicks]

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

Edited July 27, 2008 by dhicks

[maniac]

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.

[SYNACK]

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

 

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.

Edited July 27, 2008 by SYNACK

[ssiruuk2]

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

[dhicks]

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... ...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.

 

--

David Hicks