hi friends...
i have tried my best to educate you about the bluetooth technology in this blog.Though everything about bluetooth cannot be covered,anyone intrested in knowing about bluetooth technology from scratch will definitely find this useful.
BLUETOOTH BASICS:-
Bluetooth is a cable-replacement technology designed to wirelessly connect peripherals, such as mice and mobile phones, to your desktop or laptop computer and to each other. An inexpensive, low-power,short-range radio-based technology, Bluetooth is not a wireless networking solution, such as AirPort.Rather, it is an alternative to the IrDA (Infrared Data Association) standard. Although the IrDA
standard, too, supports wireless communication between peripherals and computers, it has two limiting requirements. First, IrDA devices must be very close, no more than about 1 meter apart.Second, the communicating devices must have a direct line of sight to each other.Because it relies on radio waves, however, Bluetooth communication overcomes these strict
requirements:
■ Bluetooth devices can communicate at ranges of up to 10 meters.
■ Bluetooth devices do not need to be in direct sight of each other.
This makes Bluetooth communication much more flexible and robust. It’s also important to note that because Bluetooth excels at low-bandwidth data transfer, it is not intended as a replacement for high-bandwidth cabled peripherals. For high-bandwidth devices, such as external hard drives or video cameras, cables are still the best option.
BLUETOOTH ARCHITECTURE:-
Bluetooth is both a hardware-based radio system and a software stack that specifies the linkages between layers. This supports flexibility in implementation across different devices and platforms.It also provides robust guidelines for maximum interoperability and compatibility.In this section, you’ll learn about:
■ The Bluetooth protocol stack. The protocol stack is the core of the Bluetooth specification that defines how the technology works.
■ The Bluetooth profiles. The profiles define howto use Bluetooth technology to accomplish specific tasks.
The heart of the Bluetooth specification is the Bluetooth protocol stack. By providing well-defined
layers of functionality, the Bluetooth specification ensures interoperability of Bluetooth devices and encourages adoption of Bluetooth technology. As you can see in Figure , these layers range from the low-level radio link to the profiles.

LOWER LAYERS:-
At the base of the Bluetooth protocol stack is the radio layer. The radio module in a Bluetooth device is responsible for the modulation and demodulation of data into RF signals for transmission in the air. The radio layer describes the physical characteristics a Bluetooth device’s receiver-transmitter component must have. These include modulation characteristics, radio frequency tolerance, and sensitivity level.
Above the radio layer is the baseband and link controller layer. The Bluetooth specification doesn’t establish a clear distinction between the responsibilities of the baseband and those of the link controller.The best way to think about it is that the baseband portion of the layer is responsible for properly formatting data for transmission to and from the radio layer. In addition, it handles the synchronization
of links. The link controller portion of this layer is responsible for carrying out the link manager’s commands and establishing and maintaining the link stipulated by the link manager.The link manager itself translates the host controller interface (HCI) commands it receives into baseband-level operations. It is responsible for establishing and configuring links and managing power-change requests, among other tasks.
You’ve noticed links mentioned numerous times in the preceding paragraphs. The BluetootH specification defines two types of links between Bluetooth devices:
■ Synchronous, Connection-Oriented (SCO), for isochronous and voice communication using,for example, headsets
■ Asynchronous, Connectionless (ACL), for data communication, such as the exchange of vCards Each link type is associated with a specific packet type. A SCO link provides reserved channel bandwidth for communication between a master and a slave, and supports regular, periodic exchange of data with no retransmission of SCO packets.An ACL link exists between a master and a slave the moment a connection is established. The data packets Bluetooth uses forACL links all have 142 bits of encoding information in addition to a payload that can be as large as 2712 bits. The extra amount of data encoding heightens transmission security. It also helps to maintain a robust communication link in an environment filled with other devices
and common noise.The HCI (host controller interface) layer acts as a boundary between the lower layers of the Bluetooth protocol stack and the upper layers. The Bluetooth specification defines a standard HCI to support Bluetooth systems that are implemented across two separate processors. For example, a Bluetooth system on a computer might use a Bluetooth module‘s processor to implement the lower layers of the stack (radio, baseband, link controller, and link manager). It might then use its own processor to implement the upper layers
(L2CAP,RFCOMM, OBEX, and selected profiles). In this scheme, the lower portion is known as the Bluetooth module and the upper portion as the Bluetooth host.Of course, it’s not required to partition the Bluetooth stack in thisway. Bluetooth headsets, for example,combine the module and host portions of the stack on one processor because they need to be small and self-contained. In such devices, the HCI may not be implemented at all unless device testing is required.
Because the Bluetooth HCI is well defined, you can write drivers that handle different Bluetooth
modules from different manufacturers. Apple provides an HCI controller object that supports a USB implementation of the HCI layer.
UPPER LAYERS:-
Above the HCI layer are the upper layers of the protocol stack. The first of these is the L2CAP (logical link control and adaptation protocol) layer. The L2CAP is primarily responsible for:
■ Establishing connections across existing ACL links or requesting an ACL link if one does not
already exist
■ Multiplexing between different higher layer protocols, such as RFCOMMand SDP, to allow many different applications to use a single ACL link
■ Repackaging the data packets it receives from the higher layers into the form expected by the
lower layers.
The L2CAP employs the concept of channels to keep track of where data packets come from and
where they should go. You can think of a channel as a logical representation of the data flow between the L2CAP layers in remote devices. Because it plays such a central role in the communication between the upper and lower layers of the Bluetooth protocol stack, the L2CAP layer is a required part of every Bluetooth system.Above the L2CAP layer, the remaining layers of the Bluetooth protocol stack aren’t quite so linearly ordered. However, it makes sense to discuss the service discovery protocol next, because it exists independently of other higher-level protocol layers. In addition, it is common to every Bluetooth device.
The SDP (service discovery protocol) defines actions for both servers and clients of Bluetooth services. The specification defines a service as any feature that is usable by another (remote) Bluetooth device. A single Bluetooth device can be both a server and a client of services. An example of this is the Macintosh computer .

This was all about bluetooth architecture.you can find more information on
http://www.bluetooth.com/bluetooth/
About bluetooth application development visit.
http://www.computer.org/portal/cms_docs_ieeecs/ieeecs/education/csidc/2001ProjectReports/NationalTaiwan.pdf

I hope to cover more about Bluetooth technology in my next blog....till then...happy blogging...