Re: upper limit of bonded devices?

[Peter Dons Tychsen <donpedro@tdcadsl.dk>]

Hi Iain & Garry,

On Tue, 2010-04-06 at 20:57 +0100, Iain Hibbert wrote:
> Sure, but consider that the page timeout (time to failure of a
> connection
> attempt) is usually around 20 seconds.. and most Bluetooth controllers
> (that I have tried) can only page a single device at a time.. So, if
> you
> don't know which devices are in range, you might be waiting a *long*
> time
> before you connect to anything..

20 seconds for a "page-timeout" is unusual for the reason you just
mentioned. However, the "link-timeout" is usually around 10-20 seconds,
but that is only applicable if an existing links needs to drop. The page
timeout use usually more like 3-5 seconds. Even if it were as high as
you describe, it is easily re-configurable. Going below ~2 seconds is
not a good idea though as you push the odds of hitting the page-scan
window (i do not remember the exact number, look in the spec). Even
better test it (and tune accordingly). For an application like this you
want a low page-timeout.

On Tue, 2010-04-06 at 19:11 +0100, Iain Hibbert wrote:
> you will probably find that because the HS device is very limited in
> resources, it does not keep records of more than one paired device.
> So, if
> you pair with another device it forgets about the first and you will
> not
> be able to connect except that you pair it again.

Many headset devices store store 8 devices they have previously paired
with (the major brands). It is however not a guarantee, so some might
not have it.

>On Tue, 2010-04-06 at 13:08 -0400, Garry Paxinos wrote:
> Is there a practical upper limit of the number of devices that can be
> bonded to a single computer?

The number of devices is almost limitless. However, as Iain said, in
theory this cannot be done with one controller as the maximum devices
for a unit is 7. In practice it looks even worse, as many controllers
become unstable if you go beyond 2 links. The link itself also becomes
unstable when many devices are connected, as you run out of air-time
(your radio can only service one at any time), and you risk loosing a
link. I recommend people to stick with one link pr. application if
stability and speed is the name of the game. If not, test it!

Recently i created a large setup of lots of BT-USB dongles connected via
some hubs to a single box running Bluez. To my delight it was remarkably
easy and stable. The well designed Bluez-API really is a bonus. Doing
this on any other system has only ended in agony. Just having that many
USB devices can cause problems on many systems. This is definitely the
way to go if you are trying to connect to lots of devices in a reliable
way. It is pretty cheap as well, as even good dongles are getting
cheaper even as i type (down to $10-$15)! :-)

Good luck on your project,

Thanks,

/Pedro