Технологии


Bluetooth

The principle of operation is based on the use of radio waves. Bluetooth radio is carried out at ISM-band, which is used in various household appliances and wireless networks (free from licensing range 2,4-2,4835 GHz). In the method of Bluetooth spread spectrum frequency hopping. FHSS method is simple to implement, provides stability to the broadband noise, and inexpensive equipment. 
The algorithm FHSS, the carrier frequency in the Bluetooth signal abruptly changes 1600 times per second (79 entire operating frequency is allocated a width of 1 MHz). The switching sequence between the frequencies for each compound and is known only to the pseudorandom transmitter and receiver that every 625 microseconds (one timeslot) are rearranged synchronously with one carrier frequency to another. Thus, if there are several transmitter-receiver pairs, then they do not interfere with each other. This algorithm is also an integral part of a system to protect the confidentiality of information transmitted: the transition occurs at a pseudorandom algorithm and is determined separately for each connection. When transmitting digital data and audio (64 kbit / s in both directions) using different coding schemes: the audio is not repeated (usually), and digital data in case of loss of information packet will be retransmitted. 
Bluetooth protocol support not only the compound point-to-point, but also the connection «point-to-multipoint». 
Bluetooth has a layered architecture consisting of a core protocol, cable replacement protocols, telephony control protocols and borrowed protocols. Binding protocols for all Bluetooth stacks are: LMP, L2CAP and SDP. Furthermore, devices that communicate with the Bluetooth HCI protocol is usually used, and RFCOMM. 
Initializing bluetooth-connection is called the installation process communication. It can be divided into three steps: 
1) Key generation Kinit 
2) Key Generation Communications (it is called link key and denoted as Kab) 
3) Authentication