4 linksys srx routers in one ballroom?

Discussion in 'Networking Issues' started by Fmwoodall, Dec 14, 2005.

  1. Fmwoodall

    Fmwoodall Network Guru Member

    We have a large ballroom (300 by 600 feet) that we want to setup a wireless network for. We currently have planned to place 4 linksys srx200 routers one in each corner. I am assumming each one will operate on a different channel. Each display table when they turn on their wireless notebook will see one or more of the routers at which point they can simply choose to connect to one. We hope having the routers in the corners will help load balance across the different routers since some display tables will not pick up the signal from the opposite corners. There will be large objects hanging from the 40 foot high ceiling to reflect/bounce/interfere with the signals. Currently the only need is to reach the internet not other systems in the room. Therefore we were going to configure each router in a different LAN subnet and have the WAN address to match the wired cable plant subnet.
    Any thoughts or ideas are appreciated. :)
  2. howardp6

    howardp6 Network Guru Member

    Try channels 1, 4, 8 and 11.
  3. cgondo

    cgondo Network Guru Member

    i think 4 is a bit overkill. Being a ballroom (meaning open space) i would imagine 2 or 3 should be more than enough.
  4. NateHoy

    NateHoy Network Guru Member

    Actually, I gotta be honest - I have to imagine that two would be overkill, unless I'm missing something. They are looking at hooking to the Internet, so channel saturation won't be a real issue. 802.11b is more than enough bandwidth unless it's one heck of an Internet connection.

    I'd just put one of them dead center in the room (in the ceiling, if possible). That gives a maximum direct-line of 300 feet or so plus elevation to the ceiling. Maybe put a higher gain antenna on it for safety, load up aftermarket firmware and boost the antenna signal a bit, but I can't imagine not being able to cover 300 feet. It's not like the signal has to penetrate walls or heavy obstacles.

    Worst case, two of them, located along the longer centerline at ceiling height, 1/3 of the way into the room each. That gives a maximum distance of 150 or so feet, for those vendors crammed all the way in the corners. It also cuts down on signal interference with any adjacent rooms.
  5. Fmwoodall

    Fmwoodall Network Guru Member

    Don't forget stuff hanging from ceiling

    Great ideas everyone. Don't forget large objects (like several entire aircraft!) hanging from the ceiling. There will be additional aircraft on the floor. Some tables will be under wings, etc. There may be as many as 400 wireless devices attempting to access the wireless network. Everyone wants "fast" access to the internet.
    These are some of the reasons we were considering 4 routers.
  6. NateHoy

    NateHoy Network Guru Member

    Re: Don't forget stuff hanging from ceiling

    400 clients!!! Phew!

    How big is your pipe to the Internet? You're going to need some serious bandwidth to support that crowd. ;)

    Hmmm.. OK, you may want two of them just for the load balancing, if nothing else.
  7. vincentfox

    vincentfox Network Guru Member

    3, or 4 just for load-balancing. Many AP's choke just from too many AP's associating at once. How many is too many? Depends on the vendor, and don't believe the lies of the salesman, try it yourself.

    Ditch the SRX junk and get yourself some plain old WRT54GS units with ability to add your own antenna.

    Considering your locations, a "corner" reflector antenna would be ideal. The HawkingTech 15 dBi corner antenna for example is one I have used. Just use the same SSID, but different channels, would be simplest. A client will associate with whichever AP is closest, solving your load-balancing problem without having to educate them to connect to SSID "NE-corner" when they are in the northeast-corner, etc. Channels 1, 6, and 11 for 3 APs, or channels 1, 4, 8, and 11 for 4 APs. Sufficient channel separation and interference can be a big problem if not understood and managed.

    Actually if load does turn out to be a problem, more AP's could in fact solve it without interfering with each other if carefully planned. The idea would simply be run reduced power on each AP and focused antenna with less "leakage" to keep the bubbles small. One way I would do this for instance would be the WiFi equivalent of a canister light. Put a high-gain directional in the ceiling pointing straight down, set AP to minimal transmit power. It's focused cone of coverage would let you pack in more AP's as long as you stagger them so that no neighboring AP is using a channel closer than 3-4 separation. Get it?

    Some firmware offer an "AP isolation" checkbox which is supposed to keep clients from infecting each other, sniffing traffic, etc.
  8. sufrano63

    sufrano63 Network Guru Member

    a wireless router can only support up to 30 or 32 concurrent users. With up to 400 users connecting at the same time....you'll probably gonna need more than 4 routers.
  9. Fmwoodall

    Fmwoodall Network Guru Member

    Thanks! great ideas

    Thanks everyone. Those are some great ideas. We have a 10 MB cable modem installation. Yes...our cable provider is running a full 10 MB now. Access is quick!
    I was thinking about SRX to get the improved range. I like the standard 54g with higain directional antennas.
    I appreciate everyones thoughts and ideas.
  10. atinexus

    atinexus Network Guru Member

    dont forget also 1 router can only dhcp 253 client
    so you will have to set different subnets
  11. danielhaden

    danielhaden Network Guru Member

    Wow, I'm impressed! What kind of ballroom is that? Four hundred clients is standing room only for most ballrooms.

    Use the WRT54GS or GL and shut off "frame burst" wireless option. The fastest and most stable firmware for this machine is Thibor's HyperWRT version 201105.

    Multiple SRX cannot co-exist. Each uses multiple channels. Every channel is 3 channels "fat" or wide. There are only eleven channels total. MIMO technology, like SRX, will not work for you to support such a great volume of wireless clients.
    SRX/MIMO technology is useless unless the wireless clients have been upgraded to SRX/MIMO.

    The GS model is extraordinarily adept at supporting clients in a radio dense environment while also not interfering with other wireless routers.
    The reason to buy it over the "G" model is that the "GS" is far more likely to work well.
    Speedbooster, the premium feature of the "GS" still provides a mild boost (6% to 10%) to clients even if they do not have matching technology.

    The older models, version 3 and earlier will do the best job for you (see the Autopsy feature of linksysinfo.org to get the identification guide--buying locally, the serial numbers are printed on the box and identify the units). Newer models, version 4 and the "GL" can be successfully pressed into service (more information about loading Thibor's HyperWRT on the V4 and GL is available at the forums of hyperwrt.org)--and the only difference that matters is the slight added difficulty in loading the firmware onto the newer models. The GL is very inexpensive to mail order.

    For 400 clients, you will not want to enable roaming because too many clients could end up on one single wireless router. Make the SSID's different for all 8 wireless routers.

    Maximum load for a given wireless router is about 45 clients. They could do 50 in a pinch. 400 clients means 8 wireless routers.
    Bear in mind that a small coffee shop can overload a wireless router. That's why you need 8 as a bare minimum.

    For this reason, use channels 1, 8, 4, 11 and then repeat this pattern, but keep identical channels far apart as possible.

    The panel and corner antennas are helpful in order to insure great quality service. Any directional antenna can do this job. It must include a R-TNC plug or R-SMA to R-TNC adaptor. Such adaptors may be purchased seperately. Directional antennas will not receive interference from other nearby networks unless the antenna is specifically pointed that direction. That is why you need directional antennas.

    Should you choose to use only one upgrade antenna per wireless router, software, such as HyperWRT, can control which antenna jack is in use. Be aware that you will need to field test each one because some of them are backwards. As you face the wireless router's display lights, the right side antenna jack is soldered directly to the mainboard and usually produces the strongest signal with the WRT54GS.

    The factory antennas can be directional in that the power and reception does not come out of the tip or end--only the broadside produces power and reception. This does not work as well as purchasing directional antennas, but it certainly does work.

    If there will be old-style "B" devices that must be included, they will not operate in such a dense environment unless you enable "CTS Protection" which will help them get connected at the expense of dropping the performance of the "G" devices. Without this feature, the "B" devices will not connect in your environment. Most "B" devices cannot use WPA security, and so you would be reduced to WEP security if you include these old style devices. Unfortunately, most PDA's run on wireless "B" along with a very few laptops.

    Some style of security, even if not totally effective, must be included for your clients. Without security, passwords for E-mails and finances, etc. . . are broadcast in the clear. Even old security, such as the very insecure WEP, is good enough to scramble up most passwords and at least inconvenience the attacker. You may post the log-in information on the menu/agenda/flyer or on a sign that is located on/near the wireless router. All of their WEP numerical passcodes may be the same. Use only a manually-set number (not word) as the passcode.

    Hopefully, you will be able to use WPA+TKIP protection along with CTS protection Disable and forget about "B" wifi. For best results, include a number or two in with the password. If you cannot use WPA because of the need to support a great variety of WIFI, then you can still do well with WEP.

    Consider an open (zero security) network only if your clients will not be entering valuable information. Also consider an open network if you need not to provide connection support to clients, because an open network will connect clients automatically with no support staff necessary.
    With this, any neighbors will join your network with zero effort while they download illegal materials (copies of music/movies) using your internet connection (with your name on it) and download passwords and personal information from 400 clients. Ease of support still might be worth it, but do consider carefully.

    For Internet-only service, plug all of the wireless routers into their own wired network that is not connected to your company's network. Connect this between your firewall and your internet service. In this way, you will not accidentally connect your Internet customers (and, possibly, your neighbors) into your company's private network. However you arrange it, do not use WDS-AP combination mode to connect the wireless routers into a wireless mesh because that cuts in half the number of clients that each may serve. With that many clients, you must run an ethernet cable to each wireless router. That can be very useful. . .

    You may use a power-over-ethernet adaptor if there is no electrical outlet at the place where the wireless router will be installed. In fact, this is the recommended approach so that you can plug them all into safe power, such as a (at least) 600VA AVR-equipped backup battery (like a nice, cheap Ultra 1000). This way, your network won't go out every time there is a little blip in the electrical power.

    Good luck getting 400 computers along with their 400 human operators into a ballroom. I'd like to see that! ;)

    Your current internet connection will fail with 400 clients who simultaneously access the Internet. You have half as much bandwidth as you need and zero guarantee that it will work at all. You need a commercial quality load balanced ethernet-only router that can combine two seperate sources of Internet into one single fault-tolerant source of Internet. From there, go into a commercial quality network switch that will power your eight wireless routers. And, every element of your network should be plugged into some sort of backup battery and never directly into an outlet.

    Wireless routers can be disguised inside anything made of plastic or paper. So, if there are just too many blue boxes with rabbit ears, you can easily find a container, signage (informational sign), or artwork of some sort to disguise them. Wall or ceiling mounting is a nice option as well.
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