Bluetooth Communication Query

I want to clear of my basics before I Jump into more complicated matter of bluetooth. I have following basic question.

1. If there is two bluetooth devices(A phone and a bluetooth display). Is it that bluetooth connection is initiated only by the phone.

2. Suppose there would be lot of bluetooth communication happening from a phone to bluetooth display.Both devices can send messages to any other devices at any time. What is usual design approach of communication. Is it that the phone creates a Socket Connection to the bluetooth display through RFCOMM first time by sending a connect request to the Bluetooth device and this connection is maintained all the time or for every message the Socket connection is made and then socket is closed, after that again reopened and closed for next message.

3. If 开发者_StackOverflowthe connection is opened till the devices are in nearby range what are the consequences.

4. What is normal way of communication in case of phone and headset.

5. Can I get any reference so that i can get some knowledge about that.

1) In general, bluetooth connections can be initiated by either device. For example, with a phone and computer, you could start a connection from either side. With a phone and a display or headset, there may be no input interface on one device, so you would initiate connections from the phone. Devices can also auto-negotiate role switches such that they swap master/slave roles.

2) If you have continuous data to exchange, or require low latency, the connection would typically be left up. If you only have rare messages to exchange, tearing down the connection would save power because the devices are maintaining the connection synchronization by exchanging null packets.

3) You can't maintain a connection with devices out of range. If they can't communicate for some timeout period (on the order of seconds) then they lose sync and kill the connection.

4) Note that phone/headset are not using RFCOMM connections, rather the HSP (headset profile). Connections for isochronous voice data are inherently different than a sporadic data connection like RFCOMM.

5) A good way to see how "real" devices are communicating is to use tools like hcidump, as part of the linux blueZ stack. This lets you fully sniff the protocol messages that happen as you connect devices.