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.
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.
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.
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.
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.
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