[Bluez-devel] Broadcast A2DP

[Bluez-devel] Broadcast A2DP

[Mayank Batra]

Guys,

Is it possible to develop an application, that will
broadcast a2dp stream to more than 1 sink?

Something like an FM station?

What I want to know is that whether sufficient
bandwidth will be there or not?


Mayank

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Re: [Bluez-devel] Broadcast A2DP

[Marcel Holtmann]

Hi Mayank,

> Is it possible to develop an application, that will
> broadcast a2dp stream to more than 1 sink?

it will be possible.

> What I want to know is that whether sufficient
> bandwidth will be there or not?

I think it is not and besides this you might get into problems if you
create a scatternet. Most headphones I have seen require to be a master
of a piconet. Thus means that the source will create a scatternet and
the link manager must use hold mode to switch between both piconets. In
all my tests this was not working very good.

Regards

Marcel




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Re: [Bluez-devel] Broadcast A2DP

[Brad Midgley]

Mayank,

>>What I want to know is that whether sufficient
>>bandwidth will be there or not?
> 
> I think it is not and besides this you might get into problems if you
> create a scatternet.

I suspect my itech clip is only insisting on being master if you 
"connect" (just rfcomm, not sco) it first to the phone. Maybe Marcel 
could clear it up if I'm wrong. Here's what I observe:

If the headset is connected (again, just rfcomm) and I start an a2dp 
stream to it from the computer, it works fine until I move my bluetooth 
mouse. The audio breaks up when the mouse is moving. What I suspect 
happens is the computer is master to the mouse and slave to the headset. 
I think the computer gives priority to its own piconet.

If the headset is not "connected" to the phone and I send music to it, I 
can move the mouse and there is no loss of audio. Trying to initiate the 
connection from phone to headset briefly causes the music to stop but 
the phone connection fails and the music starts again. It seems to me 
that the headset is just a slave device and won't be able to accept the 
incoming connection.

Brad


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Re: [Bluez-devel] Broadcast A2DP

[Mayank Batra]

Marcel,
> 
> > Is it possible to develop an application, that
> will
> > broadcast a2dp stream to more than 1 sink?
> 
> it will be possible.
> 
> > What I want to know is that whether sufficient
> > bandwidth will be there or not?
> 
> I think it is not and besides this you might get
> into problems if you
> create a scatternet. Most headphones I have seen
> require to be a master
> of a piconet. Thus means that the source will create
> a scatternet and
> the link manager must use hold mode to switch
> between both piconets. In
> all my tests this was not working very good.


Consider the simple case, when the headphones will not
want to become the master of the piconet, so, there
will be only a single piconet with the a2dp source as
the master. Thus no scatternet.
(IVT's BlueSoleil, for instance, does not require to
be master)

Now, my question is, whether I can send a broadcast
packet on the L2CAP layer. If yes, then how?

Or will I have to send packets one after the other to
all the sinks. If this is the case then I'm afraid
that we'll face shortage of bandwidth, cause after sbc
encoding, bit rates are no less than 210 kbps, which
means that no more than 3 sinks can be supported (for
a bandwidth of 723 kbps).

Also, I read somewhere that at L2CAP level, we can
form groups similar to IGMP. Is that true? or rather,
is it there in Bluez?



Mayank Batra


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Re: [Bluez-devel] Broadcast A2DP

[Marcel Holtmann]

Hi Mayank,

> > > Is it possible to develop an application, that
> > will
> > > broadcast a2dp stream to more than 1 sink?
> > 
> > it will be possible.
> > 
> > > What I want to know is that whether sufficient
> > > bandwidth will be there or not?
> > 
> > I think it is not and besides this you might get
> > into problems if you
> > create a scatternet. Most headphones I have seen
> > require to be a master
> > of a piconet. Thus means that the source will create
> > a scatternet and
> > the link manager must use hold mode to switch
> > between both piconets. In
> > all my tests this was not working very good.
> 
> Consider the simple case, when the headphones will not
> want to become the master of the piconet, so, there
> will be only a single piconet with the a2dp source as
> the master. Thus no scatternet.
> (IVT's BlueSoleil, for instance, does not require to
> be master)
> 
> Now, my question is, whether I can send a broadcast
> packet on the L2CAP layer. If yes, then how?
> 
> Or will I have to send packets one after the other to
> all the sinks. If this is the case then I'm afraid
> that we'll face shortage of bandwidth, cause after sbc
> encoding, bit rates are no less than 210 kbps, which
> means that no more than 3 sinks can be supported (for
> a bandwidth of 723 kbps).

I think you have to do it this way. If you get into bandwidth problems,
then use more dongles.

> Also, I read somewhere that at L2CAP level, we can
> form groups similar to IGMP. Is that true? or rather,
> is it there in Bluez?

You mean the L2CAP connection less channel. We have basic support for
it, but not really the group management part. However what you need for
real broadcast is broadcast support on the HCI level. Otherwise the
kernel have to emulate the broadcast for you and this is the same as
above.

Regards

Marcel




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