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Establishing Connections in Bluetooth

This section describes the basic procedures to be followed by two or more Bluetooth devices to start a connection between themselves. Consider the following scenario: A person walks in to a hotel lobby and wants to access her email over her Bluetooth enabled device, which could be a laptop or a Personal Digital Assistant. What would she have to do?

Depending on the implementation., she would be clicking on a menu or an email application icon. The device would automatically carry out the following steps, (except perhaps for the authentication step if the device has come to the environment for the first time):

  1. Inquiry: The device on reaching a new environment would automatically initiated an inquiry to find out what access points are within its range. (If not, it'll do so when the email application asks for a link.) This will result in the following events:
    1. All nearby access points respond with their addresses.
    2. The device picks one out the responding devices.
  2. Paging: The device will invoke a baseband procedure called paging. This results in synchronization of the device with the access point, in terms of its clock offset and phase in the frequency hop, among other required initializations.
  3. Link establishment: The LMP will now establish a link with the access point. As the application in this case is email, an ACL link will be used. Various setup steps will be carried out as described below.
  4. Service Discovery: The LMP will use the SDP (Service Discovery Protocol) to discover what services are available from the access point, in particular whether email access or access to the relevant host is possible from this access point or not. Let us assume that the service is available, otherwise, the application cannot proceed further. The information regarding the other services offered at the access point may be presented to the user.
  5. L2CAP channel: With information obtained from SDP, the device will create an L2CAP channel to the access point. This may be directly used by the application or another protocol like RFCOMM may be run over it.
  6. RFCOMM channel: Depending on the need of the email application an RFCOMM or other channel (in case of other applications) will be created over the L2CAP channel. This feature allows existing applications developed for serial ports to run without modification over Bluetooth platforms.
  7. Security: If the access point restricts its access to a particular set of users or otherwise offers secure mode communications to people having some prior registration with it, then at this stage, the access point will send a security request for "pairing". This will be successful if the user knows the correct PIN code to access the service. Note that the PIN is not transmitted over the wireless channel but another key generated from it is used, so that the PIN is difficult to compromise. Encryption will be invoked if secure mode is used.
  8. PPP: If a PPP link is used over serial modem as in dial up networking, the same application will now be able to run PPP over RFCOMM (which emulates the serial port). This link will allow the user to login to his email account.
  9. Network Protocols: The network protocols like TCP/IP, IPX , Appletalk can now send and receive data over the link.

In the above procedure, user interaction is required only at the usual login for his email and additionally for the security to be implemented. The remaining steps are automatic.



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