L2CAP , RFComm , SDP and Piconets in IoT

L2CAP

• The Logical Link Control and Adaptation Protocol (L2CAP)
• Layered over the Baseband Protocol and resides in the data link layer.
• Used to multiplex multiple logical connections between two devices.
• Provides connection-oriented and connection data services to upper layer protocols.
• Provides :

             - Protocol multiplexing capability
             - segmentation and reassembly operation
             - Group abstractions


RFComm

• Radio Frequency Communication (RFCOMM).
• It is a cable replacement protocol used for generating a virtual serial data stream.
• RFCOMM provides for binary data transport.
• Emulates EIA-232 (formerly RS-232) control signals over the Bluetooth baseband layer, i.e. it is a serial port emulation.
• RFCOMM provides a simple reliable data stream to the user, similar to TCP.
• Supports up to 60 simultaneous connections between two BT devices.

Service Discovery Protocol (SDP)

• Enables applications to discover available services and their features.
• Address the unique characteristics of the Bluetooth environment such as, dynamic changes in the quality of services in RF proximity of devices in motion.
• Can function  over a reliable packet transfer protocol.
• Uses a request / response model.

Piconets

• Bluetooth enabled electronic devices connect and communicate wirelessly through short range networks known as Piconets.
• Bluetooth devices exist in small ad-hoc configuration with the ability to act either as master or slave.
• Provisions are in place, which allow for a master and a slave to switch their roles.
• The simplest configuration is a point to point configuration with one master and one slave.
• When more than two Bluetooth devices communicate with one another , it is called a PICONET.
• A Piconet can contain up to seven slaves clustered around a single master.
• The device that initializes establishment of the Piconet becomes the master.
• The master is responsible for transmission control by dividing the network into a series of time slots amongst the network members, as a part of time division multiplexing scheme.

Features of Piconet

• Within a Piconet , the clock and unique 48-bit address of master determines the timing of various devices and the frequency hopping sequence of individual devices.
• Each Piconent device support 7 simultaneous connections to other devices.
• Each device can communication with several piconets simultaneously.
• Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave piconets.
• A device can be a slave in one Piconet and master in another . It however cannot  be a master in more than once Piconets.
• Devices in adjacent Piconets provide a bridge to support inner-Piconet connections, allowing assemblies of linked Piconets to form a physically extensible communication infrastructure known as Scatternet.

Applications

• Audio players
• Home automation
• Smartphones
• Toys
• Hands free headphones
• Sensor networks