Establishing A Connection


This section describes the basic procedures to be followed by two or

more Bluetooth devices to start a connection between them.


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):



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:


- all nearby access points respond with their addresses.


- the device picks one out the responding devices.




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.


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 on the following pages.


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.


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.


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.



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.


Network Protocol

The network protocols like TCP/IP, IPX, Appletalk can now send and

receive data over the link.



Assuming that 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.



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. The above procedures now are described in detail to

demonstrate the connection establishment process. The explanation

of the above procedures require a brief description the device clocks

in Bluetooth.