Protocol Stack for IEEE 802.15.1 Standard

• IEEE 802.15.1 Standard more commonly known as Bluetooth, is a low-data-rate, low-power wireless networking standard aimed at replacing cables between lightweight devices.
• The Bluetooth stack defines many components above the PHY and MAC layers, some of which are optional.
• This type of design permits the Bluetooth Special Interest Group to compose these components into application-specific profiles.
• The protocols in the Bluetooth standard can be loosely grouped into the Physical Layer, Data Link Layer, Host Controller Interface (HCI), Middleware Layer, and Application Layer

1. Physical Layer

• All Bluetooth devices are required to implement this layer in hardware.
• The protocols in this layer are designed to allow devices to locate and connect.
• This layer consists of protocols such as Bluetooth Radio and Baseband.

Bluetooth Radio

• This Bluetooth Radio layer dictates the frequency, power, and modulation used by Bluetooth antennas.
• It is responsible for searching other devices, assigning master and slave roles.
• This is laid down the physical structure and specifications for transmission of radio waves.
• It defines air interface, frequency bands, frequency hopping specifications, and modulation techniques.

Baseband

• This layer controls the Bluetooth unit’s synchronization and transmission frequency hopping sequence.
• It manages the link between devices and determines packet types supported for synchronous and asynchronous traffic.
• This protocol takes the services of radio protocol.
• It defines the addressing scheme, packet frame format, timing, and power control algorithms.

2. Data Link Layer

• Protocol in this layer carry audio and data traffic where audio traffic has higher priority.
• It supports synchronous and asynchronous transmission for telephony-grade voice communication.
• This layer consists of Link Manager Protocol (LMP), and Logical Link Control and Adaptation Protocol (L2CAP).

Link Manager Protocol (LMP)

• LMP establishes logical links between Bluetooth devices and maintains the links for enabling communications.
• This layer also supervises devices pairing.
• The other main functions of LMP are device authentication, message encryption, bandwidth allocation, and negotiation of packet sizes.
• It is also responsible for power control and may request adjustments in power levels.

Logical Link Control and Adaptation Protocol (L2CAP)

• All data traffic is routed through this layer.
• This layer shields higher layers from details of lower layers.
• It segments larger packets from higher layers into smaller packets that can be easily handled by lower layers.
• It facilitates maintenance of the desired grade of service in two peer devices.
• It supports both connection-oriented as well as connectionless services.

3. Host Controller Interface (HCI)

• The HCI allows higher layers of the stack, including applications, to access the baseband, link manager, etc., through a single standard interface.
• Manage physical and logical links between devices so that layers above and applications can pass data through connections.
• It serves the purpose of interoperability between host devices and Bluetooth modules.
• HCI commands, the module may enter certain modes of operation. Higher layers are informed about certain events through HCI.

4. Middleware Layer

The protocols in this group are needed for existing applications to operate over Bluetooth links. - These protocols may be third-party protocols (Industry standard) or developed by ‘Simple Interest Group (SIG)’ specifically for Bluetooth. - Protocols in this layer are as follows::

RFCOMM

• It provides a serial interface with WAP.
• It provides a virtual serial port for applications needed for scenarios like dial-up networking, etc.
• This eliminates the use of cables. Hence, it is also called as Cable Replacement Protocol.

Service Discovery Protocol (SDP)

• The SDP is a standard method for Bluetooth devices to discover and learn about the services offered by other devices once a connection is established with it.
• The SDP takes care of service-related queries.

Infrared Data Association(IrDA) Interoperability Protocols

• The SIG has adopted some IrDA protocols to ensure interoperability between applications to exchange a wide variety of data.

Object Exchange Protocol (OBEX)

• It is developed by IrDA to exchange objects simple and spontaneous manner.
• It uses the client-server model.
• It is independent of the transport mechanism and transport ‘Application Programming Interface (API)’, provided it realizes a reliable transport base.
• It defines a folder-listing object, which is used to browse the contents of folders on a remote device.

Networking Protocols

• Bluetooth wireless technology uses peer-to-peer network topology.
• Dial-up networking uses AT commands. which contains an ATtention command set.
• In most cases, network accessed is an IP network with the use of standard protocols like TCP, UDP, HTTP
• A device can connect to an IP network using the network access point. The internet PPP is used to connect to the access point.

Telephone Control Specifications (TCS BIN) and Audio

• This is designed to set up voice calls.
• It supports functions like call control and group management.
• TCS can also be used to set up data calls.
• TCS protocols are compatible with ITU Specifications.
• Bluetooth Audio communication takes place at the rate of 64Kbps using one of two encoding schemes: 8-bit logarithmic PCM or continuously variable slope delta modulation.

5. Application Layer

• This group consists of actual applications that make use of Bluetooth links and refers to software that exists above the protocol stack.
• The Bluetooth-SIG does not define any application protocols nor does it specify any API.
• Bluetooth profiles are developed to establish a base point for use of a protocol stack to accomplish a given usage case