BLUETOOTH LAYER

              Bluetooth layer uses several layers that do not exactly match those of the internet model . The below fig shows these layers ,

• The bottom layer is the physical radio layer , which is corresponds to the physical layer in the OSI and 802 models . It deals with radio transmission and modulation .
• The base band layer is  somewhat similar to the MAC sub layer but also includes elements of the physical layer . It deals with how master controls time slots and how these slots are groped into frames .
• The link manager handles the establishment of logical channels between devices , including power management , authentication , and quality of service .
• The logical link control adaptation protocol shields the upper layers from the details of transmission . It is analogous to the standard 802 LLC sub layer , but technically different from it .
• The next layer up is the middle ware layer , which contains a mix of different protocols . The 802 LLC was inserted here by IEEE for compatibility with its other 802 networks  .
• The RF comm , telephony , and service discovery protocols are native . RF comm(Radio frequency communication) is the protocol that emulates the standard serial port found on PCs for connecting the keyboard , mouse , and modem , among other devices . It has been designed to allow legacy devices to use it easily .
• The telephony protocol is a real time protocol used for the three speech oriented profiles . It also manages call setup and termination . Finally , the service discovery protocol is used to locate services within the network .
• The top layer is where the applications and profiles are located . They make use of the protocols in lower layers to get their work done . Each application has its own dedicated subset of the protocols . Specific devices , such as a headset , usually contain only those protocols needed by that application and no others . 

RADIO LAYER:-

• The radio layer moves the bits from master to slave , or vice versa . It is a low power system with a range of meters operating in the 2.4-GHz ISM band . The band is divided into 79 channels of L MHz each .
• Bluetooth uses the frequency - hopping spread spectrum (FHSS) method in the physical layer to avoid interference from other devices or other networks .
• Bluetooth hops 1600 times per second , which means that each device changes its modulation frequency 1600 times per second .
• A device uses a frequency for only 625 micro seconds (1/1600 s) before it hops to another frequency; the dwell times is 625 microseconds .
• To transform bits to a signal , Bluetooth uses a sophisticated version of FSK called GFSK (FSK with Gaussian bandwidth filtering) . GFSK has a carrier frequency .
• Bit 1 is represented by a frequency deviation above the carrier; bit 0 is represented by a frequency deviation below the carrier .
•  The frequencies , in MHz are defined according to the following formula for each channel:           Fc = 2402+n                    where n= 0,1,2,3,............,78 .

                   

                             For example : the 1st channel uses carrier frequency 2402 MHz (2.402 GHz) , and the 2nd channel uses carrier frequency 2403 MHz (2.403 GHz) .

BASE BAND LAYER :-

• The base band layer is roughly equivalent to the MAC sub layer in LAN's . It turns the raw bit stream into frames and defines some key formats .
• The primary/ master and secondary/ slaves communicate with each other using time slots. The length of a time slot is exactly the same as the dwell time , 625 microseconds this means during the time that one frequency is used , a sender sends a frame to a secondary is a secondary sends a frame to the primary .
• The communication is only b,w the primary and a secondary; secondary's cannot communicate directly with one another . The master's transmissions starting in the even slots and the slave's transmissions starting in the odd ones .
• Bluetooth uses a form of TDMA that is called TDD - TDMA (TIME DIVISION DUPLEX TDMA) is a kind of half - duplex communication in which the secondary and receiver send and receiver data , but not at the same time (half - duplex)