Re: Wireless for a grocery store
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Posted by Jeff Liebermann on September 19, 2008, 12:29 pm
Please log in for more thread options On Thu, 18 Sep 2008 12:30:55 -0400, Dagwood Bumstead I just "bricked" a WRT54G v2 and can't seem to recover. Argh. Might as well do something else, like answer questions... Hint: It's never as cheap as you plan. >In wireless roaming, what happens if two similarly SSID'ed and
>Channel'ed WAPs overlap? If the channels overlap, you'll have mutual interference from both AP's but only if both are in use. If you have two client radios, each talking to seperate AP's, they will interfere with each other. If one AP is idle, there's tiny bit of interference from broadcasts and beacons, but not much else. The SSID doesn't matter. Identical SSID's are not a problem because the client can distinguish AP's by their MAC addresses. There are huge wireless networks, all running the same SSID. The problem is that the client software usually doesn't have any control over which of the AP's to connect. It searches for suitable AP's by SSID, and connects to any AP with the right SSID based up criteria that varies from strongest signal to random chance. If the client picks the wrong AP, it may take an act of divine intervention to convince the client radio to rescan for a better connection. The client software is designed to be tenacious and will continue to use the initial AP even if the signal strength has become useless. Only when the signal disappears completely, or sometimes the error rate is high enough to qualify as useless, does the client initiate a disconnect and scan for another AP. Some client software offer some control over this effect (i.e. Intel Proset) but generally, it's a nightmare. >Big question here: what about range extenders?
It will cost you $50 to answer that question. Buy a range extender, any range extender or repeater. Set up a wireless network inside a closed area (to minimize outside interference). Install exactly one wireless AP or router. Add one laptop client radio. Run a thruput benchmark test using IPerf or JPerf. Now, add a range extender into the room. Retest. Last time I did this, the thruput dropped to about 1/3 of normal. The moral is that range extenders (and mesh networks) work very when the client and the AP cannot see each other, and work miserably when they can create mutual interference. >One of the reasons for
>wireless is the inconvenience of wiring out the entire building. That's the usual reason. Have you consider the alternative methods of PowerLine, PhoneLine, and CATV cable networking? >Would
>range extenders, where we would only have to get power to them (which >is already there) provide a reasonable solution? In my never humble opinion, they suck. Note that others disagree. I've tried them in various configurations and actually found a few situations where they were functional and useful (i.e. point to point path to get over an obstacle). However, for an enclosed area, no way. >I wouldn't have to
>range extend the whole way... I could put WAPs at either end and in >the middle, and then use range extenders to fill in, if that is valid >solution. Too many radios in too small an area too much potential for mutual interference. You could isolate the areas using directional antennas, but methinks the design, planning, testing, and cost will break your unspecified budget. >Would you do G or N?
G. N is all about speed, not range. N does better (on paper) in a highly reflective environment and might be worth looking at if reflections become an issue. However, G is good enough for your unspecified application. You'll also find that when the signal becomes marginal, N client radios will revert to G. If you're expecting marginal signals, you might as well start with G. >Lastly, do you know of any inexpensive products that might provide
>some central management to these devices? SNMP. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | ||||||||||
>able save a couple $...