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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

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