Re: [Bluez-devel] Re: Lower granularity for INQUIRY interval

[Marcel Holtmann <marcel@holtmann.org>]

Hi Catalin,

> > > Is there a way to perform INQUIRY for intervals with
> > > a lower granularity than 1.28 seconds? I know the Bluetooth
> > > specification says no.
> 
> > To inquire for less than 10.24 seconds is a bad idea. Unless you
> > inquire for a single contiguous block lasting 10.24 seconds you do not
> > have a good probability of picking up all devices.
> >
> > Note that, for example, 8 consecutive 1.28 second inquiries is not
> > guaranteed to work.
> 
> Not necessarily a bad idea. In my case, I need to do symmetric Bluetooth
> discovery. There are no predefined roles (master-slave, server-client) for
> the devices which must continually scan their surroundings in order to
> discover other devices. Hence, each device must continously switch between
> the INQUIRY and INQUIRY SCAN states. Since in my setup, the devices will
> be in range for 20-30 seconds (i.e. humans walking past each other), to
> remain for 10.24 seconds in INQUIRY mode might just me too much. Imagine
> that the "phases" of the devices are almost synchronized, then they will
> both be in INQUIRY mode at the same time, then in INQUIRY SCAN mode at the
> same time, and so on, and none of them will discover the other one.
> 
> The problem has been studied both theoretically and experimentally (for
> example, see:
> http://web.informatik.uni-bonn.de/IV/Mitarbeiter/scholz/10_Bohman.pdf
> 
> The conclusion of the authors of this study was that each a device should
> stay in each of the two states for a random amount of time with a mean
> around 2 to 3 seconds (more details, are in the above paper). Doing this
> yields and average neighbor discovery delay of about 8 seconds.
> 
> Now obviously if we can only stay in INQUIRY state mode, for multiples of
> 1.28 seconds, the above scenario will not work. So there are _legitimate_
> uses (i.e. it is not necessarily a bad idea) for my request.

I still don't get why switching inquiry scan on and off should help in
any case. Since inquiry scan defines the discoverable mode and so you
switch devices to unvisible when they inquiry and back to visible when
they don't.

Regards

Marcel




-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
_______________________________________________
Bluez-devel mailing list
Bluez-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/bluez-devel