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Limits to Bluetooth Inquiries

Posted on 2004-09-14
Medium Priority
Last Modified: 2013-12-14
I have written a simple Bluetooth application (using the Windows CE Widcomm SDK) which merely scans for devices in the area. I have only tested this with two other devices and it works fine.
I would like to know if anyone has done any experiments to see what the maximum number of devices one inquiring device could find? I know that the limit to forming a piconet is 7, but my application is much simpler - just seeing what's out there.
I have programmed an iPAQ h4100 which will happily find my DLink dongle and Nokia cellphone. If I add another iPAQ things start getting a bit confused. I'm not sure if its my program or the Bluetooth radio on the device. I have found with the iPAQ that the Bluetooth radio is a little buggy, sometimes it won't find my dongle at all, if I just use the native device discovery on the PDA.

Any suggestions, former experience would be greatly appreciated,
Question by:SamKite
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Accepted Solution

pierrel2 earned 1000 total points
ID: 12071927
The answer depends a great deal on the particular implementation.  I cannot comment on the CE Widcomm SDK, but in the case of one of the embedded Widcomm stacks, we found that the limit was determined more by the total string length that is built up from the concatenation of all the services on all the local Bluetooth devices.

This is to say that having a small number of devices with LOTS of services seems to "use up" the available space more easily than lots of devices with one or two services each.

As there are a myriad of different versions of these stacks out there, your mileage will vary, but this may give you a rule-of thumb.

Discovery should always work; but sometimes it doesn't.  Try again.  Watch out for antenna saturation if the devices are too close.  Good luck!

Author Comment

ID: 12072598
Thanks very much for your help.
I didn't consider the service side of things but it makes sense now that you mention it!

I was also wondering in terms of number of concurrent connections - for instance using RFCOMM (Virtual Serial Ports)- there must be some upper limit to the number of concurrent virtual connections one device could have with many others? I know that Bluetooth transmits on one port and listens on another, and I realise that these are not 'real' ports but surely there is some limit for this?
Sam :-)


Expert Comment

ID: 12077751
I'm not 100% sure what you're trying to accomplish here.  Bluetooth limits the number of concurrent connections to 7.   Within a single connection with a device, there can, at least theoretically, be several different communications channels (though I'm not clear why you would want to do this), each multiplexed over a single RFCOMM link.  

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