Hi,
I think having understood the main concepts of RFCOMM
connections (DLC, DLCI ...) however I really wonder about
multi processing (globally and in BlueZ specifically)
- If I want to write a service (published in the SDP) for example
on channel 9, can I write a forking server (forking at each accept
so it can accept a new incoming connection from another
remote device while the first connection is being managed ?)
We assume we have only one bdaddr (bluetooth adaptor) in local
I suppose it could lead to 2 concurrent connection tuples like these ones :
( (local_bdaddr, channel 9) - (remote1_addr, channel9) )
( (local_bdaddr, channel 9) - (remote2_addr, channel9) )
Is it possible ? Without any conflicts ? I know on the local service
we would have the same DLCI for both sockets. In TCP it would be
possible with REUSEADDR, would it be the same here ?
- Now taking a reverse problem, let's assume I have a client
application that will "push" content to mobile phones, on channel 9.
Can I run concurrent pushers on my computer ?
Concurrent tuples would look like the same as formerly, except
that the server / client roles are reversed here.
Thanks a lot for helping me, believe I have searched a lot before
asking !
Oli
Hi Peter,
> > > > I think having understood the main concepts of RFCOMM
> > > > connections (DLC, DLCI ...) however I really wonder about
> > > > multi processing (globally and in BlueZ specifically)
> > > >
> > > > - If I want to write a service (published in the SDP) for example
> > > > on channel 9, can I write a forking server (forking at each accept
> > > > so it can accept a new incoming connection from another
> > > > remote device while the first connection is being managed ?)
> > > > We assume we have only one bdaddr (bluetooth adaptor) in local
> > > >
> > > > I suppose it could lead to 2 concurrent connection tuples like these ones :
> > > > ( (local_bdaddr, channel 9) - (remote1_addr, channel9) )
> > > > ( (local_bdaddr, channel 9) - (remote2_addr, channel9) )
> > > >
> > > > Is it possible ? Without any conflicts ? I know on the local service
> > > > we would have the same DLCI for both sockets. In TCP it would be
> > > > possible with REUSEADDR, would it be the same here ?
> > >
> > > This would not be possible. You can only have have one connection on a
> > > single server channel number (SCN). This is not a problem of BlueZ but a
> > > general Bluetooth issue. It may be possible to change the bluetooth stack
> > > in a way which will support a scenario aas described above, but I think
> > > this won't be a trivial task. And I'm not sure if it will still comply to
> > > the standard.
> >
> > actually this works perfectly fine. On each ACL link between two devices
> > you have 30 RFCOMM channels in one direction and another 30 in the other
> > direction. All RFCOMM restrictions are per ACL link.
>
> Ok, I think I've to get into this a little bit deeper. I think it's right
> that the RFC restrictions in general are per ACL link (or more precise per
> multiplexer session). On the other hand you can only have one
> listening session on a single SCN at a time. This means you have to fork a
> new listener once a session is started, right ?
that is how sockets work. You call listen() to create the actual
listener and then accept() for every connection. You can't have two
different listener that wanna listen on the same RFCOMM channel, but
that is also true for TCP/IP.
However you can bind one listener to BDADDR_ANY and the other one to the
actual address of the local dongle, but in that case the listener bound
to the local address always wins.
Regards
Marcel
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Hi Marcel,
On Sun, 29 Oct 2006, Marcel Holtmann wrote:
> Hi Peter,
>
> > > I think having understood the main concepts of RFCOMM
> > > connections (DLC, DLCI ...) however I really wonder about
> > > multi processing (globally and in BlueZ specifically)
> > >
> > > - If I want to write a service (published in the SDP) for example
> > > on channel 9, can I write a forking server (forking at each accept
> > > so it can accept a new incoming connection from another
> > > remote device while the first connection is being managed ?)
> > > We assume we have only one bdaddr (bluetooth adaptor) in local
> > >
> > > I suppose it could lead to 2 concurrent connection tuples like these ones :
> > > ( (local_bdaddr, channel 9) - (remote1_addr, channel9) )
> > > ( (local_bdaddr, channel 9) - (remote2_addr, channel9) )
> > >
> > > Is it possible ? Without any conflicts ? I know on the local service
> > > we would have the same DLCI for both sockets. In TCP it would be
> > > possible with REUSEADDR, would it be the same here ?
> >
> > This would not be possible. You can only have have one connection on a
> > single server channel number (SCN). This is not a problem of BlueZ but a
> > general Bluetooth issue. It may be possible to change the bluetooth stack
> > in a way which will support a scenario aas described above, but I think
> > this won't be a trivial task. And I'm not sure if it will still comply to
> > the standard.
>
> actually this works perfectly fine. On each ACL link between two devices
> you have 30 RFCOMM channels in one direction and another 30 in the other
> direction. All RFCOMM restrictions are per ACL link.
Ok, I think I've to get into this a little bit deeper. I think it's right
that the RFC restrictions in general are per ACL link (or more precise per
multiplexer session). On the other hand you can only have one
listening session on a single SCN at a time. This means you have to fork a
new listener once a session is started, right ?
Ciao,
Peter
| Peter Wippich Voice: +49 30 46776411 |
| G&W Instruments GmbH fax: +49 30 46776419 |
| Gustav-Meyer-Allee 25, Geb. 12 Email: [email protected] |
| D-13355 Berlin / Germany |
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Hi Peter,
> > I think having understood the main concepts of RFCOMM
> > connections (DLC, DLCI ...) however I really wonder about
> > multi processing (globally and in BlueZ specifically)
> >
> > - If I want to write a service (published in the SDP) for example
> > on channel 9, can I write a forking server (forking at each accept
> > so it can accept a new incoming connection from another
> > remote device while the first connection is being managed ?)
> > We assume we have only one bdaddr (bluetooth adaptor) in local
> >
> > I suppose it could lead to 2 concurrent connection tuples like these ones :
> > ( (local_bdaddr, channel 9) - (remote1_addr, channel9) )
> > ( (local_bdaddr, channel 9) - (remote2_addr, channel9) )
> >
> > Is it possible ? Without any conflicts ? I know on the local service
> > we would have the same DLCI for both sockets. In TCP it would be
> > possible with REUSEADDR, would it be the same here ?
>
> This would not be possible. You can only have have one connection on a
> single server channel number (SCN). This is not a problem of BlueZ but a
> general Bluetooth issue. It may be possible to change the bluetooth stack
> in a way which will support a scenario aas described above, but I think
> this won't be a trivial task. And I'm not sure if it will still comply to
> the standard.
actually this works perfectly fine. On each ACL link between two devices
you have 30 RFCOMM channels in one direction and another 30 in the other
direction. All RFCOMM restrictions are per ACL link.
> > - Now taking a reverse problem, let's assume I have a client
> > application that will "push" content to mobile phones, on channel 9.
> > Can I run concurrent pushers on my computer ?
> > Concurrent tuples would look like the same as formerly, except
> > that the server / client roles are reversed here.
> This won't be a problem as long as you just have a single connection to
> each remote device. The reason is that for every outgoing connection a new
> local channel will be allocated which is independend from he remote server
> channel you connect to.
Precisely and it the same for incoming connections.
Regards
Marcel
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Hello Oli,
On Fri, 27 Oct 2006, Olivier Le Pogam wrote:
> Hi,
>
> I think having understood the main concepts of RFCOMM
> connections (DLC, DLCI ...) however I really wonder about
> multi processing (globally and in BlueZ specifically)
>
> - If I want to write a service (published in the SDP) for example
> on channel 9, can I write a forking server (forking at each accept
> so it can accept a new incoming connection from another
> remote device while the first connection is being managed ?)
> We assume we have only one bdaddr (bluetooth adaptor) in local
>
> I suppose it could lead to 2 concurrent connection tuples like these ones :
> ( (local_bdaddr, channel 9) - (remote1_addr, channel9) )
> ( (local_bdaddr, channel 9) - (remote2_addr, channel9) )
>
> Is it possible ? Without any conflicts ? I know on the local service
> we would have the same DLCI for both sockets. In TCP it would be
> possible with REUSEADDR, would it be the same here ?
This would not be possible. You can only have have one connection on a
single server channel number (SCN). This is not a problem of BlueZ but a
general Bluetooth issue. It may be possible to change the bluetooth stack
in a way which will support a scenario aas described above, but I think
this won't be a trivial task. And I'm not sure if it will still comply to
the standard.
> - Now taking a reverse problem, let's assume I have a client
> application that will "push" content to mobile phones, on channel 9.
> Can I run concurrent pushers on my computer ?
> Concurrent tuples would look like the same as formerly, except
> that the server / client roles are reversed here.
This won't be a problem as long as you just have a single connection to
each remote device. The reason is that for every outgoing connection a new
local channel will be allocated which is independend from he remote server
channel you connect to.
Ciao,
Peter
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