Talking about the Bluetooth protocol stack

For a brief introduction to the Bluetooth protocol stack, we need to first have a concept for the bluetooth technology. I believe that everyone can learn what they need. Let's take a look at the specific content.

1. Introduction to Bluetooth Technology

Bluetooth Technology originated in 1994 and was initially designed to eliminate wired connections between various electrical devices. With the in-depth research and application requirements, Bluetooth technology has been able to provide various voice and data devices, such as PCs, dial-up networks, laptops, printers, fax machines, mobile phones, digital cameras, high-quality headphones, etc., connect them to a micro-network Piconet through wireless ), allows seamless resource sharing between various devices.

Bluetooth works in the global 2.4GHzISM band and uses the frequency hopping technology to overcome interference and decline. The frequency hopping bandwidth is 79 MHz, with a total of 79 RF channels, the symbolic transfer rate is 1 Mb/s. full-duplex communication using time-division TDD. information is exchanged in groups on the channel. Each group is transmitted at different frequency hops, occupying 1 to 5 time slots with a length of 625 μs.

The Bluetooth protocol combines circuit switching and group switching. It supports one asynchronous data channel, up to three synchronous voice channels, or one channel that supports both asynchronous data and synchronous voice. each voice channel supports 64kb/s bit transmission rate in each direction, asynchronous channels support asymmetric bit transmission rate up to 723.2kb/s, or 433.9kb/s symmetric bit transmission rate.

The Bluetooth system consists of a wireless unit, a link control unit, and a support unit with Link Management and Host terminal interface functions, as shown in figure 1.

The Bluetooth system provides point-to-point or point-to-point connections. in a one-to-multiple-point connection, several Bluetooth units share the same channel to form a micro-Network, one of which serves as the main unit of the micro-network, other slave units can activate up to 7 ). channel access is controlled by the main unit. the micronetworks with overlapping coverage areas constitute a scattered network (Scatternet ). the time-division multiplexing of units can be used to add different micro-networks. In addition, the master unit of a micro-network must also be the slave unit of another micro-network. these micro-networks are not synchronized in time or frequency, and each network has its own frequency hopping channel.

2. Bluetooth protocol stack

Figure 2 shows a complete Bluetooth protocol stack. different applications run on different protocol stacks. However, each protocol stack uses the same bluetooth data link layer and Bluetooth physical layer. figure 2 also shows how Bluetooth uses other existing protocols for business when wireless data transmission is required.

As shown in figure 2, the complete Bluetooth protocol stack consists of Bluetooth-specific protocols [such as LMP Link Management Protocol), L2CAP Logical Link Control and Adaptation Protocol)], and non-Bluetooth-specific protocols [such as OBEXObjectExchangeProtocol) udpuserpolicramprotocol)] two parts.

The main principle for designing Bluetooth and protocol stacks is to maximize the reuse of existing protocols at the High Level Based on different application purposes. in this way, existing applications and Bluetooth technologies can coexist and ensure their interoperability. furthermore, due to the openness of Bluetooth technology standards, various developers can freely run their own or public application protocols on the Bluetooth protocol.