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Multiple bluetooth connection

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Anonymous
July 21, 2004 12:03:51 PM

Archived from groups: alt.cellular.bluetooth (More info?)

Hi all,

I have several questions about bluetooth (BT), any input will be
greatly appcreciated.

1) Can a normal BT phone talks to multiple BT phones at the same time?

2) If there are 10 BT phone within an area and they try to talk to
each other, how will BT protocol handle the queueing? is it FIFO or
LIFO?

3) What is the average time needed for a handshake between two BT
phone?
For Handshake I mean: Two phone finds each other->connection
established->disconnected and go back to discovery mode.

Many thanks,
Jon.
Anonymous
July 21, 2004 8:30:43 PM

Archived from groups: alt.cellular.bluetooth (More info?)

jonearth wrote:

> 1) Can a normal BT phone talks to multiple BT phones at the same time?
>

Yes

But most services offered by phones are point-to-point, hence the number of devices
participating in the service session is equal to two. But you could have a
PhoneA-to-PhoneB synchronisation session running at the same time as a PhoneA-to-HeadsetY
connection.

> 2) If there are 10 BT phone within an area and they try to talk to
> each other, how will BT protocol handle the queueing? is it FIFO or
> LIFO?

Bluetooth has a special network topology scheme to enable multiple devices to form a small
network termed a *piconet*. This piconet consists of a single master and upto seven
*active* slaves. more slaves may be *connected* but not considered *active*.

The master has complete control over how the piconet is run. Slaves may not "talk" to each
other, and may only communicate with the master immediatly after it has been addressed by
the master..

This is termed polling, the master polls the slave. The slaves are polled at the
discretion of the master but may negotiate some Quality-Of-Service parameters to try and
acheive any required data rates.

The polling scheme is completely implementation independant (master), Round robin would be
the simplest but consider a fairly complex priority based scheduler

>
> 3) What is the average time needed for a handshake between two BT
> phone?
> For Handshake I mean: Two phone finds each other->connection
> established->disconnected and go back to discovery mode.

From "Bluetooth Application developers guide" [ISBN: 1-928994-42-3] chapter 1,pp23

Table 1.2 Connection times to set up an active bluetooth link

Min Average Max (seconds)
Inquiry 0.00125 3-5 1.24-30.72
Page 0.0025 1.28 2.56
Total 0.00375 4.28-6.28 12.8-33.28

These figures are from a book that was written against Bluetooth spec 1.0b
new features from spec 1.2 greatly improve connection times.

Hope this helps

Rob
July 22, 2004 7:43:06 AM

Archived from groups: alt.cellular.bluetooth (More info?)

Rob Shepherd <robshep@invalid.invalid> wrote in message news:<cdm273$9f4$1@fantastix.bangor.ac.uk>...
> jonearth wrote:
> > 1) Can a normal BT phone talks to multiple BT phones at the same time?
> Yes

I'm afraid I'm going to have to disagree with you here. I have tried
this with multiple phones, and at least with the ones I've tried, this
isn't true.

On the N-Gage, Ericsson R520m, Ericsson T39m and SonyEricsson
P800/P900, if there is an active bluetooth headset connection, you can
not do RFComm serial over Bluetooth. The converse is true - if I am
connected via RFComm to my phone, it won't let me use the headset.

> But most services offered by phones are point-to-point, hence the number of devices
> participating in the service session is equal to two. But you could have a
> PhoneA-to-PhoneB synchronisation session running at the same time as a PhoneA-to-HeadsetY
> connection.

If only the implementation on the phone supported it...

Now, maybe I'm doing something wrong, maybe my USB dongle is too old,
or I can do something special to make this work, but I haven't been
able to make it work.

gopi.
Related resources
Anonymous
July 22, 2004 12:06:27 PM

Archived from groups: alt.cellular.bluetooth (More info?)

Rob Shepherd <robshep@invalid.invalid> wrote in message news:<cdm273$9f4$1@fantastix.bangor.ac.uk>...
> jonearth wrote:
>
> > 1) Can a normal BT phone talks to multiple BT phones at the same time?
> >
>
> Yes
>
> But most services offered by phones are point-to-point, hence the number of devices
> participating in the service session is equal to two. But you could have a
> PhoneA-to-PhoneB synchronisation session running at the same time as a PhoneA-to-HeadsetY
> connection.
>
> > 2) If there are 10 BT phone within an area and they try to talk to
> > each other, how will BT protocol handle the queueing? is it FIFO or
> > LIFO?
>
> Bluetooth has a special network topology scheme to enable multiple devices to form a small
> network termed a *piconet*. This piconet consists of a single master and upto seven
> *active* slaves. more slaves may be *connected* but not considered *active*.
>
> The master has complete control over how the piconet is run. Slaves may not "talk" to each
> other, and may only communicate with the master immediatly after it has been addressed by
> the master..
>
> This is termed polling, the master polls the slave. The slaves are polled at the
> discretion of the master but may negotiate some Quality-Of-Service parameters to try and
> acheive any required data rates.
>
> The polling scheme is completely implementation independant (master), Round robin would be
> the simplest but consider a fairly complex priority based scheduler
>
> >
> > 3) What is the average time needed for a handshake between two BT
> > phone?
> > For Handshake I mean: Two phone finds each other->connection
> > established->disconnected and go back to discovery mode.
>
> From "Bluetooth Application developers guide" [ISBN: 1-928994-42-3] chapter 1,pp23
>
> Table 1.2 Connection times to set up an active bluetooth link
>
> Min Average Max (seconds)
> Inquiry 0.00125 3-5 1.24-30.72
> Page 0.0025 1.28 2.56
> Total 0.00375 4.28-6.28 12.8-33.28
>
> These figures are from a book that was written against Bluetooth spec 1.0b
> new features from spec 1.2 greatly improve connection times.
>
> Hope this helps
>
> Rob

Thanks Rob, your information is very useful to a newbie like me.

I have one more question. Do you know if I can send data in UDP
packets format from one phone to another?

I have read some materials these days and it looks like BT connection
are all TCP-liked. So I am wondering if UDP is available in BT. The
application I want to write don't need reliable message transfer, just
like when u are streaming audio you don't need to receive every
packets. The only requirement is to have a fast, quick and simple way
to exchange data between two phones.
Anonymous
July 22, 2004 4:34:23 PM

Archived from groups: alt.cellular.bluetooth (More info?)

gopi wrote:
> Rob Shepherd <robshep@invalid.invalid> wrote in message news:<cdm273$9f4$1@fantastix.bangor.ac.uk>...
>
>>jonearth wrote:
>>
>>>1) Can a normal BT phone talks to multiple BT phones at the same time?
>>
>>Yes
>
>
> I'm afraid I'm going to have to disagree with you here. I have tried
> this with multiple phones, and at least with the ones I've tried, this
> isn't true.
>
> On the N-Gage, Ericsson R520m, Ericsson T39m and SonyEricsson
> P800/P900, if there is an active bluetooth headset connection, you can
> not do RFComm serial over Bluetooth. The converse is true - if I am
> connected via RFComm to my phone, it won't let me use the headset.
>

Of course it's implementaton dependant, but I was speaking purely as an avid Specification
reader.

There may be an issue with "Who-is-the-master-and-what-will-it-allow" ..

Think of it from the master point of view... you have paged a device and connected and so
you are controlling the network, but along comes another device and tries to page you..
If it were to succeed you would be it's slave as well as still being master yourself.

So some implementations just disable page-scanning whilst being a master, but there is one
further option, the master-slave switch, whereby the would-be-master#2 will page as normal
but switch to slave role as soon as the connection is made...

> If only the implementation on the phone supported it...

Of course, but the original question was very general, so my answer was based purely on
Specification details.

Rob
Anonymous
July 22, 2004 8:58:18 PM

Archived from groups: alt.cellular.bluetooth (More info?)

jonearth wrote:

> Thanks Rob, your information is very useful to a newbie like me.
>
My pleasure,


> I have one more question. Do you know if I can send data in UDP
> packets format from one phone to another?

Bluetooth is basically just a carrier for packets of any kind and carries data from node
to node in it's own data packet format.

To make things easy i shall start at the top.

RFCOMM is a protocol which emulates a standard serial port connection over radio from
point to point, just like a cable, and uses a subset of some GSM spec or other to put the
data into frames.

These frames are passed down to the l2cap layer where multiple channel are multiplexed and
segmented in l2cap packets which are of length specified by the maximum receive and
transmit MTU (maximum transmission unit)of each side and is upto 65535 bytes.

these l2cap packets are transmitted from l2cap engine to l2cap engine via the radio
baseband, which uses packets of variable length.

The length is variable because of the unreliability of the radio interface. So for a nice
quiet environment the maximum baseband packet size is 339 bytes but for noisy environments
with lots of interference the packet size can drop to 17 bytes with a discrete scale in
between (i won't elaborate).

Packets which are lost through interference are retransmitted by the sender by request of
the recipient so if it's noisy and packets are retransimitted a lot, it makes sense to
make each packet as small as possible to make retrasmissions quicker. [bear in mind an
entire packet is lost through interference, if just one or two bits is corrupt]

So for TCP traffic the protocol used is called BNEP, bluetooth network encapsulation
protocol and this wraps ethernet frames into l2cap packets.

BNEP sits alongside (not above or below) RFCOMM.

Profiles which make use of BNEP are PAN (personal area networking) and some others which
actually may wrap PAN also.

so after that ramble, Yes if your device supports BNEP and can provide a BNEP network
interface then it can wrap TCP/UDP/IP/ethernet frames.

But i would be very surprised if phones supported this because they are generally used as
DCE (data communications equipment, such as modems) equipment... Syncing is generally
thought of as being done locally through IrDA and bluetooth with LOCAL machines or PDA's.

Newer smart phones however which have PDA functions and the like, may have this functionality

hth

Rob
July 23, 2004 10:23:32 AM

Archived from groups: alt.cellular.bluetooth (More info?)

Rob Shepherd <robshep@invalid.invalid> wrote in message news:<cdo8nv$ro$1@fantastix.bangor.ac.uk>...
> Of course it's implementaton dependant, but I was speaking purely as an
> avid Specification reader.

The original question said "most phones", and in my experience most
phones don't permit it. The spec does, but the implementations don't
seem to.

Do you know of any phones that can use a headset and concurrently do
RFComm to another device?

I understand what you're saying about the spec - it's carefully
designed to permit what the OP (and myself as well) would love to do.
But the implementations I've found have been lacking. My personal
experience with real hardware tells me that the answer to the OP's
question is that, no, most phones don't permit multiple connections.
I'd be happy to be proven wrong or told that if I switched headsets
from an SE HBH-65 to something else, then it would work, or anything
else really. If you select a random collection of phones and headsets,
chances are it's one at a time only.
!