For Bluetooth, the friends are already familiar and can't be cooked anymore. It's really familiar. Especially in the years when WiFi was not so common, it was not so convenient to download things online. At that time, once a small partner had any treasures of audio, video, documents, images, etc., everyone was using Bluetooth. Resource sharing. In terms of technical terms, Bluetooth is actually an open wireless communication standard, which uses the invisible cable instead of the cable to achieve the goal of “keep in touch, not cable, reject plugâ€, although its current charm is not enough.
Bluetooth introductionBluetooth is a radio technology that supports short-range communication (typically within 10m) of the device. It can exchange wireless information between many devices including mobile phones, PDAs, wireless headsets, notebook computers, and related peripherals. The standard for Bluetooth is IEEE 802.15, which operates in the 2.4 GHz band and has a bandwidth of 1 Mb/s.
"Bluetooth" was originally a king who unified Denmark in the 10th century. He unified Sweden, Finland and Denmark at that time. Using his name to name this new technical standard has the meaning of unifying the situation of being divided. Bluetooth technology uses advanced technologies such as high-speed frequency hopping (FH, Frequency Hopping) and time division multiple access (TDMA, TIME Divesion Muli-access) to inexpensively place several digital devices (various mobile devices, fixed communication devices, Computers and their terminal devices, various digital data systems, such as digital cameras, digital cameras, etc., and even various household appliances and automation devices are linked in a mesh. Bluetooth technology will be a unified bridge between the various peripheral interfaces in the network, which eliminates the connection between devices and replaces them with wireless connections.
Bluetooth protocol stackBluetooth technology is an open specification for wireless data and digital communications. Based on low-cost, close-range wireless connectivity, it establishes a complete communication method and technology for fixed and mobile devices.
The essence of Bluetooth technology is to establish a standard for universal wireless interfaces and their control software, so that mobile communication and computer networks can be seamlessly connected, thereby providing a close range (10m~100m) range for portable devices produced by different manufacturers. Interoperable channel within.
Protocol levelThe Bluetooth protocol is a kind of communication protocol. In order to simplify complex problems, any communication protocol has a hierarchy, and the characteristics are as follows:
Layered from bottom to top, each layer only needs to care about specific, independent functions, easy to implement and maintain;
Within the communication entity, the lower layer provides services to the upper layer, and the upper layer is the lower layer user;
Between communication entities, the protocol is only for each layer, and the communication between entities is just like the communication between each layer, which is conducive to communication, understanding and standardization.
The Bluetooth protocol is no exception, and its protocol hierarchy is as follows:
From the perspective of the OSI (Open System InterconnecTIon) model, Bluetooth is a relatively simple protocol that provides only two OSI layers, the Physical Layer and the Data Link Layer. However, due to the particularity of the Bluetooth protocol and historical evolution factors, the protocol level is not simple or even difficult to understand (such as Physical Link, Logical Transport, etc. shown in the above picture).
The Bluetooth protocol is divided into four levels: Physical Layer, Logical Layer, L2CAP Layer, and Application Layer.
The physical layer, which is responsible for providing the physical channel for data transmission (commonly referred to as the channel). Typically, there are several different types of channels in a communication system, such as control channels, data channels, voice channels, and the like.
The logical layer, on the basis of the physical layer, provides a logically independent logical transmission channel (also called a logical link) between two or more devices.
L2CAP layer, L2CAP is an abbreviation of Logical Link Control and AdaptaTIon Protocol, which is responsible for managing the logical links provided by the logic layer. Based on this protocol, different ApplicaTIons can share the same logical link. Similar to the concept of ports in TCP/IP.
The APP layer understands the application layer in the Bluetooth protocol and implements various application functions based on the channel provided by L2CAP. Profile is a unique concept of the Bluetooth protocol. In order to realize the interconnection and interoperability of different devices under different platforms, the Bluetooth protocol not only defines the core specification (called Bluetooth core), but also defines various Application specifications for various application scenarios. These application layer specifications are called Bluetooth profiles.
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