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Wireless Networking

Designing a Municipal Wireless Service? 42

Posted by Cliff
from the wi-fi-in-the-sky dept.
EvilTwinSkippy asks: "I am on a team generating a proposal for the Wireless Philadelphia Initiative. In short I have to figure out how to cover 135 square miles of city with Wifi. I'm reading through the requirements. (Not linking to them, no fair slashdotting the customer, or my employer.) I have already figured out that supporting Wireless B and G simultaneously has to go. As does supporting cars traveling at 60mph. And getting 1MB sustained across the network is a pipedream. In the end, I'm looking down the barrel of designing a network this is projected to have 160,000 users in 5 years, over at least 3000 nodes. I know that Rooftop mesh networks are going to be a large part of the design, as will Linux boxes acting as routers and access points. What massive network issues has 4 years of electrical engineering, and 10 years of hacking routers and servers not prepared me for?"
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Designing a Municipal Wireless Service?

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  • by Anonymous Coward
    Simply wait and copy Minneapolis' solution :)
    • by lanswitch (705539)
      Not so funny, but (hopefully) informative: check out www.wirelessleiden.nl/english . They already have an extensive wireless network, and are willing to help others wiht advice and such. See website for more.
  • by kansei (731975) on Tuesday April 12, 2005 @12:00PM (#12212647)
    Sounds like overkill - too expensive and too frail.

    Consider using dumb access points with battery backup, the kind that can be replaced easily and without much configuration. Centralize your authentication mechanism on the back end.

    • Intended for parent, not submitter - Ask yourself if every node has to have a server behind it...
      • According to the description, he is putting 3000 Linux routers/access points around the city. That's 3000 servers. I can only imagine the administration nightmare that's involved with managing that mess. A less complicated design may be easier to maintain and cheaper.
        • Why should administration on 3000 unattended servers be hard? Servers are no different than any other electronic device, so that's not an issue. Where I work, both Linux and another brand of Unix are remotely administered without fuss. In fact, so are the Windowz (Win 2000 and XP) boxes.

          I would be concerned with the scalability of the solution. I would be looking for an upgradable WiFi AP and I'd make plans for the next generation of WiFi.
        • I always RTFA but in the absence of an article, apparently I didn't RTFS (submission) that well. I speed-read it an understood it would be 3000 commodity access points and figured that one server/router could obviously administer more than one AP.

          In hindsight, that seems quite a flawed setup for this application and each AP being a full server/router seems neccessary.

          *slaps forehead*

          However, as someone else mentioned, I don't see why administering them should be so difficult. If setup properly the b
    • by rednip (186217) * <rednip@[ ]il.com ['gma' in gap]> on Tuesday April 12, 2005 @01:04PM (#12213586) Journal
      the real problem isn't just the access, it's the handoff, and coordination with other nearby access points. Cellular networks do this already. But what happens when you take a trip down the street with your little handheld PC. You need to get another IP address, those dumb access points won't coordinate with each other to provide service. I believe that is what each of those servers will be intended to do. Sure you could set the DHCP to some very low timeout, but somehow I don't think that would be a great idea. Eventually manufacturers will catch up and build specialized equipment to solve the issues, but I don't believe that any of them have so far (I could be wrong...).

      What I think that the submitter is trying to do is to find strategies to minimize 'network churn'. I have a couple of ideas on what is needed, but my lunch hour is almost up and I need to get back (my company block my attempt to post to slashdot a couple of weeks ago and I have been avoiding it at work ever since.)

      • by Anonymous Coward
        I'm not a networking guru(esp. not wireless), but if you use repeaters(those little devices that DLink/Netgear sell) and throw those all over the city, jack them into a switch with a single DHCP server and a single router .. Couldn't you escape the problem of a handoff requiring you to get a new IP?

        And in the meantime .. The submitter should probably check 802.11n specs. I realize it isn't done yet, but if you're going to wait five years, please don't start off with(what will be then) seven year old techn
        • Trouble with the repeaters option is that there is only a certain number of channels and a certain number of connections for each of those channels which a WAP (wireless access point) can address, I don't know the numbers but it's certainly not in tens of thousands if not hundreds of thousands which a city the size of Philly would need.
      • by bluGill (862)

        IPv6 is designed to solve this problem. I don't know how well it works, but if it works as well in practice as theory, you tell everyone on IPv4 that they need IPv6 to get good roaming. Maybe this would force Microsoft write a good IPv6 implementation for Windows. (yeah right)

      • My crazy idea with the roaming is to use a different netmask for the network like say 255.255.0.0 and have a dhcp server or two (@home's problems had something to do with like one server for something) to hand out IPs and then hook all of the APs up to a switch that works on the IP level, unless MAC layer is good enough (layer 3 and 2, I don't know this stuff :)

        the larger netmask lets one do things like have 10.10.10.10 use 10.10.20.1 as a gateway because 10.10.x.x are treated as local

        The other idea I had
    • Actually, I need the smarts on the edge of the network. Someone crapflooding an access point with traffic is annoying. Someone crapflooding your trunklines is a disaster. One a network this size, almost every component needs to be actively shaping traffic.

      FWIW, most of your "dumb access points" are actually running an embedded form of Linux. D-Link and LinkSys/Cisco equipment comes to mind.

  • by VernonNemitz (581327) on Tuesday April 12, 2005 @12:09PM (#12212783) Journal
    Actually, thieves will likely take more than two...
  • Yeah, hope it goes great. As I understand, this masterpiece of wireless wonder comes at the expense of the rest of the state. Under the agreement, IIRC this will be the ONLY community wireless project for PA. Of course, I'm not to sure Edward Rendell really know's that the surronding area of Philly is also PA. It just makes me wonder how many checks from Verizon and Comcast are in Mr. Rendells back pocket. That's right, I'm bitter.
    • I doubt it. His pockets are stuffed full of slots and gambling payoffs. Man I hope he runs for President.
    • For what it's worth, the City is no longer funding the project directly. They have handed it off to a 501c3 organization called "Wireless Philadelphia".

      Wireless Philadelphia is going to be putting out it's own bonds and whatnot to fund the project. I don't believe it's getting a nickel of state money. (At least not according to the financials I've seen.)

      About the only thing they have going for them over anyone else setting this up is the City's blessing to use light poles. My plan actually calls for ren

  • Seriously. 802.11b is on an UNREGULATED band. What does this mean? You can't guarantee ANYTHING. I have times when my wifi card is TOUCHING my AP, and the signal doesn't get through due to my neighbors being on their 2.4gz phone. 2.4 Ghz is NOT a band you can do a reliable service on, and any attempts to do so will be an utter disaster. Get out while you can, don't waste any more money or time on it, let everybody else get a black eye trying to do this. IMHO.
    • by MaggieL (10193)
      2.4 GHz isn't "unregulated".

      The primary allocation is to amateur radio; other users are there on a Part 15 basis, which explains your experience with your neighbor's phone. You're required to accept any interference from other devices on the band. Since I hold a licence for that band, I'm a primary user, and if interfered with by a Part 15 device can require that they fix the problem or shut down.

      If I can find them.

      • by ebrandsberg (75344)
        Now put this in context of deplying a city-wide network. See the problem? As wifi, would it classified as amateur radio or as a part 15 basis? If part 15 (as the sticker on my USB wifi adapter says), that means that if this city-wide network messed with Amateur radio services, then the city's network would have to shut down, correct? Doesn't sound safe to invest time and money into by me.
        • That's the theory. Of course, the FCC doesn't seem to be terribly concerned about the the impact on HF radio communications of baseband-over-powerline (BPL) systems, another "great technology for people underserved by the internet" move. BPL pilot projects are clearly not meeting even the lax technical standards set for them by the FCC, and yet there is no apparent enforcement action forthcoming, even though HF bands are shared by amateurs with military and homeland security users, and BLP systems aren't ev
  • Correct me if I'm wrong, but I thought G appliances were backwards compatible with B appliances.

    Seems G would be the way to go. Higher cost, but better longevity and compatibility and potential bandwidth.

    As for concerns about speed: Here's the thing that gets me about WiFi speed potential (or Ethernet for that matter) when it comes to an open network: What difference does the speed of the line to the node make as long as it's at least as fast as the pipe you'll be using on the back to connect out to the w
    • Yeah but a B device on a G network will make all G clients B. Only one chipset I know of gets around this, Conexant's Prism54 has a 'Nitro' mode which takes care of B and G clients without speed problems. I suggest you go out on the street with netstubler though, people are going to be pissed if a council installation knocks out their network.
    • Everyone is subject to regulations on output. The Armed Forces and folks like NASA get around them by having licensed communications operators.

      Boosting output may increase the range of the access point, but my problem is population density. We have 30,000 people per square mile. As it is, each access point will have to cover 80 users, even spaced 300 feet apart. Not saturating the access points is a bigger problem than range.

  • by Naikrovek (667) <`moc.gsp' `ta' `nosnhojj'> on Tuesday April 12, 2005 @01:52PM (#12214230)
    Not for a city the size of Philly but for cities of 200k people.

    Find the highest point in a particular region of town, and get the rights to put a weatherproof box and an antenna up on a tower near there. (cell phone companies are very good at finding the best points to place a tower or antenna. you should follow their lead.) in the weatherproof box put a soekris board running linux and two wireless cards and antennas on them. One card will be a backbone 802.11g link with a directional, high gain antenna, the other a customer link with a 802.11b omni antenna.

    do that for every region that needs coverage.

    Find points where multiple region APs can see, and do the same as above, but get a horizontally polarized omnidirectional antenna. they're expensive, but worth it. Connect all the regional APs to this. Run a T1 into whatever computer controls this antenna.

    do that for every group of regions.

    viola! citywide wirless. a true star topology.

    there are some details i'm leaving out, but this should give you a good idea.

    run zebra on the linux APs to handle routing.
    use backbone redundancy where possible, the APs will fail occaisionally.

    • My plan did one better. We are going to rent out space on 27 or so Cell towers spaced around the city, and run 100Mb ethenet over fiber to them. That sounds expensive, but each cell tower will be supporting up to 6000 users.

      With the right antennas, we'll never have to go more than one hop. My projections show that we charge $7.95/month and turn a profit. (Assuming we get 160,000 users by year 5.)

      The most expensive part of the project is actually the staff to maintain it.

  • Seriously. I'm doing some work for a company dealing in PreMAX (as they call it now), they have just a couple of antennaes for covering a small city. Plus WiMAX will be build into all laptops in the next years, just as wireless is now. USB plugs will be available, it will be just another revolution.

    For more information, mail me. I have an account on Yahoo named mtetrode.
  • by Anonymous Coward
    What massive network issues has 4 years of electrical engineering, and 10 years of hacking routers and servers not prepared me for?"

    In Philadelphia: union thuggery, municipal corruption, and pay to play.
  • Is this for real? (Score:4, Insightful)

    by snorklewacker (836663) on Tuesday April 12, 2005 @03:33PM (#12215560)
    Are the good citizens of PA shelling out tax dollars to fund a setup of someone who has to Ask Slashdot how to set up a municipal wi-fi network?

    3000 full-blown linux servers? Jiminy Christmas. Probably COTS PC hardware, right? Please tell me there are competing bids from experienced networking outfits?
    • by Anonymous Coward
      Please tell me there are competing bids from experienced networking outfits?

      Competitive bidding in Philadelphia? You crack me up!
      1. Are the good citizens of PA shelling out tax dollars to fund a setup of someone who has to Ask Slashdot how to set up a municipal wi-fi network?

      You expect the vendors to give better advice?

      From another angle: Even smart, experienced, people benifit from asking basic and potentially stupid questions. If they listen.

      I call that "The Columbo Method" after the TV detective of the same name.

    • We ought to forward this to every municipality in PA, in case this "sounds familiar." Some taxpayers are about to get fleeced.

      It is said that there are actually few dishonest auto mechanics, but a lot of incompetent ones. Unfortunately the same it true in IT.
  • by moorley (69393) on Tuesday April 12, 2005 @06:17PM (#12217506)
    Just some thoughts from days from working at an ISP.

    Know your scope, technically you are setting up WiFi but you need to forget about the technology for a moment and have AT LEAST a prioritized list of what this network is to be used for. Without that guiding light it will do what it does, but it may not do what anybody (or perhaps a particular high ranking somebody) will want it to do. You won't have anything to guide your decisions or your priorities.

    Second, LATENCY!
    I haven't played with WiFi meshes so this may not come in to play but from past experience with Wireless solutions ala ISP you have to remember that cabling and bandwidth is VERY IMPORTANT. Donot be tempted to use wireless repeaters with abandon. You need to be able to have a greater amount of backbone, node to node bandwidth than the nodes themselves will provide. If the wireless nodes get overloaded and TCP retransmissions (or retransmissions by the WiFi repeaters themselves) will climb and there will be a point no packets will move. The latency of WiFi will cause this packet storm (if you will) way quicker than wired solutions. Without a good amount of bandwidth behind the nodes, or even a backup landline for administration bringing it back could be quite a pain.

    The ISP I worked for tried to deploy point to point wireless bypassing the telco. Rather than run cable to the tower, they used point to point to the tower and then point to point to their customer. It didn't take long (since all of the point to point links were rated the same) for the whole solution to get snarled up bottlenecked on the point to point between the ISP and the tower. With the latency of wireless it would be unusable REALLY quick. (If only we had SQUID and bandwidth limiters back then... SIGH...)

    Lastly, you have the greatest opportunity to win through control. Your watchwords should be metrics and design. As you roll out your nodes you best be pulling metrics so you know how your design will handle load and how it will fail. This will be knowledge that is good as gold, and will allow you to re-design and re-deploy. Your first attempt will be a guess but if you capture the metrics and track as most information as you can, whether that be the temperature of the wireless nodes (do they overheat, are they sheltered, is there a pattern to failure) or the packet retransmissions; all of that information will be vital to learn how to tune it up, engineer it and deploy it.

    Have fun... I'm envious...
  • There are solutions from commercial providers for reliable metro-scale Wi-Fi mesh networks. These are installed in Philadelphia (pilot) now, New Orleans, Los Angeles, Oklahoma City, Corpus Christi, and Chaska, MN, to name just a few. Check out muniwireless.com for info about how communities around the world are doing this.
  • You can do a 100% cisco solution and get the job done right.

    Assume 20 users per AP. 200,000 users would mean that you are looking at 10,000 access points with NO redundancy. OK, you want each client to have two access points to connect to so you are going to need 20,000 access points. Now you need switches to connect to. Lets assume you can connect 400 access points to one Cisco 6500 switch. You would need 50 switches at $100,000 each. 5 million in switches and 20 million in access points. Now you n

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