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Wireless Networks Thread, WDS within a large room in Technical; Hi Folks, Quick query, hoping someone with experience or knowledge of the current situation could lend a hand/advice with a ...
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    WDS within a large room

    Hi Folks,

    Quick query, hoping someone with experience or knowledge of the current situation could lend a hand/advice with a new setup.

    One x large building, measuring roughly 30x80m. We are soon to install a wireless system, and to ensure no loss of signal anywhere in the building will be running 4 x WDS enabled wireless access points centrally placed on back wall with high-gain directional antennae (2x per AP) running in series down the back wall point toward the front.

    My understanding of WDS is limited, all I know is the AP's need to run in Repeater mode rather than Bridging as bridging turns the AP off to client connections and rather acts as a signal repeater. So Repeater mode would need to be enabled.

    Now the query:

    1) When Repeater mode is enabled, do the access points act alone regarding connections and routing, (If a laptop/device is connected via AP2, does AP2 route traffic to and from servers, or does it use a central Access point for all routing?)
    2) If a laptop/device is connected via AP1, and moves over to AP4 (AP's support Fast Roam switching) does AP4 with Repeater mode route the signal via server or does it repeat the signal across say AP4 > AP2 > AP1 > Servers and than back again via that route?

    Cheers for any answers.

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    SYNACK's Avatar
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    From my understanding WDS is a mesh type network setup that you would only use if you could not get cable infrastructure to each one. By the sounds of it these APs will each have a wired link back to the server in which case you do not want or need WDS. Just chuck them all on non-overlapping channels with the same SSID and WPA key and they will happily roam.

    I am not sure how they would behave if they were wired and WDS was enabled, you would definately have less wireless bandwidth to play with and if would only really help/route traffic if one of the cabled links went down.

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    ahuxham (24th June 2009)

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    Quote Originally Posted by SYNACK View Post
    From my understanding WDS is a mesh type network setup that you would only use if you could not get cable infrastructure to each one. By the sounds of it these APs will each have a wired link back to the server in which case you do not want or need WDS. Just chuck them all on non-overlapping channels with the same SSID and WPA key and they will happily roam.

    I am not sure how they would behave if they were wired and WDS was enabled, you would definately have less wireless bandwidth to play with and if would only really help/route traffic if one of the cabled links went down.
    Sounds like good advice.

    Any idea what the overlapping channels are? I know 1,6,11 in the UK are non-overlapping, but that only accounts for 3/4 channels needed, same SSID/WPA key will be used either way.

    Any idea for roaming change between access point? 1-5seconds? Less than 1 second? Roaming changes are the key here hence looking at some sort of "Mesh" we can't afford to lose any packets in anysense.

    The access points support IAPP as well as IEEE 802.11r which is fast roaming, however no mention of transistion timeframes.

    Cheers for the advice above.

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    I would use something like channel 2 at the far end from the chan 1 AP. I would also crank down the transmit power of each of the APs so that they cover a smaller area and you don't get as much interfearance or echo.

    As to the roaming times that will depend of the chips in your laptops, WDS will not help with this. Zero packet loss on a wireless network is also not a practical goal without much more advanced gear if many laptops are involved. TCP/IP is designed to account for this though so it should still work fine.

    The way that the roaming works 'theoredicly' is that the wireless card keeps track of all of the networks in range and their power levels, when one get weaker and another stronger it will switch over (assuming same SSID etc.). The fast roaming will prenegotiate with the network that is to be switched to before swapping over so that it is reasonably seamless (nanoseconds) but this will depend on your laptops network cards and drivers. This will also rely on you getting the power levels set right so that all of the APs just sit there banging away at full signal meaning that they all seem about as close signal strength wise to the network card. If the AP can't figure out which one is actually closer based on signal strength then it will just pick one at random (or the last one it connected to) meaning that it will broadcast possibly to the furtherst AP at high power causing even more interfearance.

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    ahuxham (24th June 2009)

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    Cheers for that SYNACK defiantly answer alot of questions

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    Was thinking about channels, and came up with the idea of using the four semi overlapping channels arrange in the order 7,1,10,4 along the back wall.

    However just read an overlapping whitepaper and 1,6,11,1 can be used provided space to stop interference. Going to have to test 7,1,10,4 and than 1,6,11,1 and see which is better.

    Any ideas for software to test such an experiment?

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    Downloads | NetStumbler.com for testing with a Windows laptop, wispy with the appropriate hardware is even better but much more expencive.

    I would be more inclined to use the primary channels over the overlapping ones at first prefference. I only suggested using chan two was as a mediation of risk if they were all turned up too high. Ideally more of channel one as it is actually a stronger channel in most situations. So I'd go with 1,6,11,1 with propperly mediated power if it is an option.

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    Quote Originally Posted by SYNACK View Post
    Downloads | NetStumbler.com for testing with a Windows laptop, wispy with the appropriate hardware is even better but much more expencive.

    I would be more inclined to use the primary channels over the overlapping ones at first prefference. I only suggested using chan two was as a mediation of risk if they were all turned up too high. Ideally more of channel one as it is actually a stronger channel in most situations. So I'd go with 1,6,11,1 with propperly mediated power if it is an option.
    Currently looking at transmit power of 100mw or 18db from the AP toward 19db(i) Directional antennae. Using 802.11b. Sensitivity at 100m should equate to -67db which is a very usable signal I hope. Will have to test more indepth.

    RE: Directional antennae, I've tested these at 200m and get around -45-55db sensitivity, the margin for their direction is very slim. I'm talking moving one foot either side and you go to around -30db which is unusable.

    On a side note: There are partitions hence the directional antennae, signal doesn't travel too well down the back with omni aerials.
    Last edited by ahuxham; 25th June 2009 at 10:39 AM.

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    I'd be wary of the directional antennas. You may find that all you do is create hot spots that work, and dead zones that don't.

    I would also recommend getting someone in that REALLY understands radio networking. From the look of the posts above, and the contradictions, it would seem that there are fundamental gaps in the knowledge base.

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    Quote Originally Posted by Andrew_C View Post
    I'd be wary of the directional antennas. You may find that all you do is create hot spots that work, and dead zones that don't.

    I would also recommend getting someone in that REALLY understands radio networking. From the look of the posts above, and the contradictions, it would seem that there are fundamental gaps in the knowledge base.
    The only dead zone from a directional antenna are too the sides, and right below it, I've more than tested it. Right below the access point is no problem as there wont need to be any coverage.

    There are fundamental gaps, as there are with anything. Who in there right might deploys a solution knowing everything is 100% covered, we're not employed on that basis we know everything about everything, more along the lines of a bit of everything and from there research/test/try/develop onwards.

    Synack has provided valuable help, clearing/explaining fundamentals I didn't quite understand. My fundamentals therefore are more clear now, and "any" contradictions cleared.

    What is a person that "REALLY" understands radio networking going to tell me that hasn't been covered, or due to be tested? Are you expert enough to undermine anything and state that what's posted, explained isn't adequate enough?

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