better way to communicate between ad hoc wifi windows mobile devices

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+2 Q:

better way to communicate between ad hoc wifi windows mobile devices

We are developing wireless ad hoc communication applications on windows mobile 6 devices using 802.11 in ad hoc mode. We are using HP iPAQ 910 devices and OpenNETCF smart device framework 2.3 for development.

As a design constraint, each device is represented as an SSID. If two devices want to communicate with each other, initiator switches to other device's SSID and broadcasts UDP messages. However this switching takes 4-5 seconds to complete and spending this much time might be undesirable in some cases. We were wondering whether there is a better and faster way in which two devices can communicate, something for which we can avoid switching SSIDs?

Please let us know if any more information is required. Thanks in advance for your help!

+3 A:

You should run them all on the same SSID. Each one will need to be configured with a unique static IP address. You can then send your messages to whichever one you want based on the IP, no switching required (i.e. it's instant). This approach will also allow you to communicate with multiple devices at the same time. You might even be able to use the UDP broadcast feature to talk to all of them at once, though I'm not sure how that works when you're on an ad hoc network.

I once built a system that used an iPAQ and a laptop both in ad hoc mode to do exactly what I just described. A joystick attached to the laptop was used to remotely control a robot which was directed by the iPAQ.

rmeador 2009-08-14 21:58:48

Thanks for your answer, rmeador! Actually we use SSIDs as a way of identifying mobile devices or IBSSs in surrounding environment. So, keeping same SSID might not work for us.

CuriousTiger 2009-08-14 22:54:41

Why not look at device MAC instead? It's guaranteed unique, and using a common SSID for all devices would certainly make deployment a whole lot easier (caveat: I've never tried this in ad-hoc mode, so YMMV)

ctacke 2009-08-15 01:51:07

Thanks for your reply, ctacke! Basically an SSID of a device or an IBSS identifies it and tells us about user applications running on it. Since SSID is a configurable entity, we thought of using it as an identifier. This might not be possible with MAC address. Alternatively, is it possible to communicate without SSID association? something like beacon-stuffing or Wi-Fi without association, as noted here: http://research.microsoft.com/en-us/groups/nrg/hotmobile07-beacon.pdf. It would be really great if we can add some application level info to 802.11 beacons.

CuriousTiger 2009-08-15 07:13:28

@CuriousTiger: the SSID is not intended to give you any information other than what network to connect to. You're misusing it, and thus you're running into problems. I can't speak to the feasibility of wifi without association or beacons, since I've never used either. I stand by my recommendation of using IPs to differentiate the handhelds, though ctacke's idea of MACs is another very good alternative.

rmeador 2009-08-17 14:20:39

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