[Bluez-users] concurrent operations

[Bluez-users] concurrent operations

[Mikael Lindqvist]

Hi,

This is a general bluetooth question...

I have been experimenting with bluetooth for some time now and I'm
wondering what is actually possible to do simultaneously. My
application is doing device discovery, service search and obex push.
It seems as if it is possible to do several obex pushes at the same
time (guess that would go for any kind of RFCOMM  connections), but
it's just possible to do one device discovery or one service search
simultaneously. I. e. it's not possible to do service search at the
same time as device discovery, and it's only possible to do service
search for one remote device at the same time.

So to sort things out once and for all, what is actually possible? And
why does this limitation exist, is it something fundamental to
bluetooth or just because of current implementations?

-- Mikael

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Re: [Bluez-users] concurrent operations

[Marcel Holtmann]

Hi Mikael,

> This is a general bluetooth question...
> 
> I have been experimenting with bluetooth for some time now and I'm
> wondering what is actually possible to do simultaneously. My
> application is doing device discovery, service search and obex push.
> It seems as if it is possible to do several obex pushes at the same
> time (guess that would go for any kind of RFCOMM  connections), but
> it's just possible to do one device discovery or one service search
> simultaneously. I. e. it's not possible to do service search at the
> same time as device discovery, and it's only possible to do service
> search for one remote device at the same time.
> 
> So to sort things out once and for all, what is actually possible? And
> why does this limitation exist, is it something fundamental to
> bluetooth or just because of current implementations?

you can't run an inquiry and a page at the same time. That is basically
all that matters. However a remote name resolve includes a page, but
that is the only exception. All the rest can run fully concurrent.

Regards

Marcel



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Re: [Bluez-users] concurrent operations

[Mikael Lindqvist]

> you can't run an inquiry and a page at the same time. That is basically
> all that matters. However a remote name resolve includes a page, but
> that is the only exception. All the rest can run fully concurrent.
>

And a "page" does that mean a service search? I've seen the term page
in the bluetooth standard but haven't really understood it. What about
several "pages" at the same time, i. e. service search for several
remote devices at the same time?

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Re: [Bluez-users] concurrent operations

[Peter Stephenson]

"Mikael Lindqvist" wrote:
> And a "page" does that mean a service search? I've seen the term page
> in the bluetooth standard but haven't really understood it. What about
> several "pages" at the same time, i. e. service search for several
> remote devices at the same time?

Paging is the period when you're trying to connect to the remote
device.  This takes variable amounts of time, depending on how
frequently the remote device is scanning.  Since scanning takes power,
most devices only scan occasionally.  For a battery powered device, once
every 1.28 seconds is typical.  Since the scan is short, it's important
that the paging device devote the entire radio bandwidth to trying to
pick up the remote device.  Hence you're stuck with not being able to do
anything else at this point.

The same argument applies to inquiry (device discovery), although it's
intrinsically unreliable --- you're not guaranteed to discover
everything.

Once connected it's possible to timeslice between different remote
devices (although there are more complicated issues to do with network
topology lurking).  The actual service search takes place when
connected, but the chances are the paging process before took longer, so
that will dominate the time.

pws


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Re: [Bluez-users] concurrent operations

[Thomas Kear]

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You pretty much summed up everything there is to say.  I see someone replied 
off the list, but I'll add what I know, in any case.

As you noted, any regular data connection can be paired with others.  The 
limit is 7 connections, but you do have to remember that there's less than 
800kbps to go around on Bluetooth 1.2 and only a couple of megabits on 
Bluetooth 2.0.  I have managed a file transfer from my cellphone (only ever 
manages 25kB/s, ~200kbps) while talking on my bluetooth headset (not sure 
about bandwidth use for it) but I don't think I'd like to test anything else 
simultaneously.

--Thomas


On Tuesday 21 November 2006 10:24 pm, Mikael Lindqvist wrote:
> Hi,
>
> This is a general bluetooth question...
>
> I have been experimenting with bluetooth for some time now and I'm
> wondering what is actually possible to do simultaneously. My
> application is doing device discovery, service search and obex push.
> It seems as if it is possible to do several obex pushes at the same
> time (guess that would go for any kind of RFCOMM  connections), but
> it's just possible to do one device discovery or one service search
> simultaneously. I. e. it's not possible to do service search at the
> same time as device discovery, and it's only possible to do service
> search for one remote device at the same time.
>
> So to sort things out once and for all, what is actually possible? And
> why does this limitation exist, is it something fundamental to
> bluetooth or just because of current implementations?
>
> -- Mikael

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