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With the development of computer and network communication technology, the use of Bluetooth technology to establish a wireless local area network not only plays a role when the office conditions are not perfect, but also has unique advantages in temporarily adding or deleting office points and mobile office services. The article introduces Bluetooth technology, and explains the networking architecture, and prospects the development trend of Bluetooth technology.
I. Introduction
In the office LAN of modern enterprises. The personal computer must log in to the local area network and the Internet within the unit to access online resources, and files, materials and equipment must be shared between the personal computers. In this way, between the PC and various peripherals, and between the PC and various shared devices. And there are many connections between the PC and the LAN socket, which brings great inconvenience to mobile office and dispatch management. The original intention of the development of Bluetooth technology is to replace the interconnected cables between various digital devices with a unified wireless communication technology. Use Bluetooth technology to set up an enterprise internal communication network. Build an Internet network platform. Not only can improve people's office environment, but also improve the modern management level of enterprises. Accelerate the office automation process of modern enterprises.
Second, Bluetooth technology
Bluetooth (Bluetooth) technology was jointly developed by Ericsson, Nokia, Intel, IBM and Toshiba in May 1998. The essence of Bluetooth technology is the wireless connection between devices, mainly used for communication and information equipment. In recent years, it has also been used in the electroacoustic industry. There are three distance classes according to the output level of the emission, Class1 is about 100m, Class2 is about 10m, and Class3 is about 2-3m. Under normal circumstances, its normal working range is within a radius of 10m. Within this range, multiple devices can be interconnected. However, for some products, the connection distance between the devices can even establish Bluetooth communication and information transfer even at a distance of 100m.
With the help of PDA personal digital assistant using Bluetooth technology, users can easily access the Internet. With Bluetooth technology, the information stored in the mobile phone can be displayed on the TV, and the sound information data can also be converted for listening on the PC. Toshiba has developed and marketed a Bluetooth Wireless Modem and PC card, one of the two cards is inserted into the host of the modem, and the other is inserted into the PC personal computer. In this way, users successfully achieved wireless networking with the Internet.
The characteristics of Bluetooth technology include: 1. The use of frequency hopping technology, short data packets, strong resistance to signal attenuation; 2. The use of fast frequency hopping and forward error correction scheme to ensure link stability, reduce co-frequency interference and long-distance transmission Random noise impact; 3. Use the 2.4GHz ISM band without applying for a license; 4. Support data, audio, and video signals simultaneously; 5. Use FM modulation to reduce the complexity of the device.
The transmission rate of this technology is designed to be 1MHz, and full-duplex communication is performed in a time-division manner. The baseband protocol is a combination of circuit switching and packet switching. A frequency hopping frequency sends a synchronous packet, each packet occupies a time slot, and it can also be expanded to 5 time slots using spread spectrum technology. At the same time, Bluetooth technology supports one asynchronous data channel or three concurrent synchronous voice channels, or one channel that simultaneously transmits asynchronous data and synchronous voice. Each voice channel supports 64 kb / s synchronous voice; the asynchronous channel supports an asymmetric connection with a maximum rate of 721 kb / s and a reverse response rate of 57.6 kb / s, or a symmetric connection with 432.6 kb / s.
At present, Bluetooth technology has been widely used in laptop computers to help wireless communication between two (or more) laptop computers. Compared with infrared transmission, it is necessary to ensure that the two devices transmitting information are right, and there must be no obstacles between them, "Almost can not control the progress of information transmission", "Not becoming a widely accepted industry standard, not many types of equipment", etc. The shortcomings of Bluetooth show the vitality of the vitality. 2161 companies worldwide have participated in the SIG (Special Interest Group) organization and are jointly developing Bluetooth technology standards. In addition to the five companies that initially proposed the development of Bluetooth technology, SIG's core companies include 3com, Lucent Technology, Microsoft, and Motorola. SIG member companies include: PC personal computers, mobile phones, network-related equipment, peripheral auxiliary equipment and A / V equipment, communication equipment and automotive electronics, vending machines, medical equipment, timing devices, and other equipment manufacturing companies.
3. Bluetooth architecture
The Bluetooth architecture includes three parts, and the composition of each part is shown in Figure 1. The following is a brief description of the hardware, software, and routing mechanism. 
1. Hardware part
1.1 RF module
The data packet of the baseband module is sent through a radio signal with a certain power and frequency hopping frequency to realize the wireless connection of the Bluetooth device.
1.2 Baseband module
Inquiry and paging methods are used to synchronize the frequency hopping clock and frequency hopping frequency, provide symmetric connection (SCO) and asymmetric connection (ASL) for data packets, and complete the definition of data packets, forward error correction, and cyclic redundancy correction Functions such as verification, logical channel selection, signal noise, authentication, encryption, encoding and decoding. It uses mixed circuit switching and packet switching, which is suitable for both voice transmission and general data transmission. Each voice channel supports 64kb / s synchronous voice, and the asynchronous channel supports an asymmetric connection with a maximum rate of 723.2kb / s (reverse 57.6kb / s) or a symmetric connection of 433.9kb / s.
2. Bluetooth protocol (software)
2.1 Link Management Protocol (LMP)
Through the transmission, exchange, identity authentication and encryption of the link, and the size of the baseband data packet is determined through negotiation, the power mode, duty cycle of the radio frequency part, and the connection status of the Bluetooth devices in the network are controlled.
2.2 Logical link control and application protocol (L2CAP)
L2CAP and LMP work in parallel to jointly realize the function of the data link layer of OSI. It can provide data services for symmetric and asymmetric connections.
2.3 Serial Cable Simulation Protocol (RFCOMM)
The function of RS-232 is emulated on the Bluetooth baseband to realize serial communication of the device. For example, in a dial-up network, the host sends AT commands to the modem and then to the local area network. After the connection is established, the application can send and receive data through the serial port provided by RFCOMM.
2.4 Service Discovery Protocol (SDP)
According to user needs, find the corresponding services and related equipment, and give a list of services and equipment. The working process is as follows: the master device broadcasts a message, the slave device responds accordingly, stores the collected address in the memory of the master device, and then the master device selects an address from it, using the process provided by the link management agent Establish a connection at the physical layer. Once the service discovery protocol is established, an LZCAP point-to-point communication layer is established on the physical layer connection between the master and slave devices.
3. Routing mechanism of wireless office network
Using Bluetooth technology to build a modern enterprise wireless office network, the basic functions achieved include: 1. Sharing and interconnection of files, archives, reports, and equipment resources, such as the interconnection between PCs, PCs and various peripherals or intelligence The interconnection and sharing of equipment; 2. The use of Bluetooth devices to wirelessly access the internal LAN and Internet of the unit; 3. The interconnection between various Peak networks within the office network through a certain routing mechanism.
According to the actual needs of the enterprise, the enterprise wireless network is composed of multiple piconets, and the communication between different piconets should only be routed within the office network, not through the local area network, which requires the establishment of a special The routing mechanism enables the communication between the Peak networks to be correctly routed, to achieve the purposes of convenient and fast communication, widening the communication range, and reducing the network load.
3.1 Bluetooth gateway
Bluetooth mobile terminals used in the office network to access the local area network and the Internet wirelessly; track and locate all Bluetooth devices in the office network, establish a routing connection between two Bluetooth devices belonging to different Pickup networks, and exchange between the devices Routing information.
The main functions include:
â‘ Realize the conversion between Bluetooth protocol and TCP / IP protocol, and complete the wireless Internet access function of the Bluetooth mobile terminal in the office network.
â‘¡ Realize the address resolution between Bluetooth address and IP address on the basis of security. It uses its own IP address and TCP port to uniquely identify Bluetooth mobile terminals without an IP address in the office network, such as Bluetooth printers.
â‘¢ The routing table is used to track and locate the Bluetooth mobile terminals in the network, so that the Bluetooth mobile terminals in the office network can access the Bluetooth mobile terminal in the local area network or another Peak network through the correct route.
â‘£ Exchange routing information between two Bluetooth mobile terminals belonging to different Peak networks, thus completing the roaming and switching of Bluetooth mobile terminal communication. In this communication method, the Bluetooth gateway acts as a relay in the process of packet routing, which is equivalent to a Bluetooth bridge.
3.2 Bluetooth mobile terminal (MT)
A Bluetooth mobile terminal is an ordinary Bluetooth device that can communicate with a Bluetooth gateway and other Bluetooth devices, so as to realize wireless Internet access of mobile terminals within an office network and sharing of files and resources within the network. The relationship between the various functional modules is shown in Figure 2.
If the destination is located in the local area network or the Internet of the unit, you need to convert the Bluetooth protocol to the TCP / IP protocol through the Bluetooth gateway. If the MT does not have an IP address, it will be provided by the Bluetooth gateway. . If the destination is located in another Peak network inside the office network, then the routing connection is established through the Bluetooth gateway, thus completing the roaming of the entire communication process. The communication method is MT-BG-M_MT (Master Mobile Terminal) -MT. Using Bluetooth technology can also connect each data terminal in the office to each other. For example, multiple terminals share one printer, and they can log in to the printer's waiting queue according to a certain algorithm and execute them in sequence.
4. Development prospects of Bluetooth technology
Bluetooth technology is an emerging technology that has not yet been widely used. At present, many Bluetooth devices are still in the laboratory test stage, and still need to be strictly tested for actual use. From the second half of 2002, the production of Bluetooth products will increase significantly, and the market will expand further. In addition to Japan, South Korea's LG, Samsung, Daewoo, and many companies in Taiwan have already begun to step into the development of Bluetooth technology and products, and some have launched finished products. Such as LG's LG-P610B, a cellular phone for PCS personal communication service. Due to the success and experience in the development and manufacturing of PCs and personal computers, the Taiwanese manufacturing industry expects that the Bluetooth industry will account for 15% of Taiwan ’s wireless communications industry in 2005, with an output value of US $ 650 million. Beginning in the summer of 2002, some manufacturers in Taiwan have begun to use Bluetooth technology in information devices such as antennas, filters, modules, notebook computers, PDAs, keyboards, and mice, and will introduce them for dongle (a type of protection software that is copied) Equipment), PCMCIA card and a LAN communication relaying device between LANs. To date, seven companies in Japan have adopted Bluetooth technology in their laptops.
The development trajectory of Bluetooth is in line with the ideal model of today's new technology development, that is, cooperation before competition. According to a survey by ABI (Allied Business Intelligence), despite the recent sluggish Bluetooth market, its development has not slowed down. ABI officials said that more and more people are considering adding wireless connections to their devices, and they are gradually realizing that Bluetooth technology's low-power and low-cost solutions are ideal. The use of Bluetooth is not limited to laptops and cell phones. Bluetooth transceivers (that is, Bluetooth cards) are increasingly embedded in various devices from PCs to industrial equipment. Bluetooth is not just a cable replacement Goods. However, ABI also reminded that there are still some obstacles to the success of Bluetooth, which are mainly manifested in the following aspects: (1) Because of the high price of silicon semiconductors, Bluetooth chips are too expensive to be popular for a while. (2) The implementation of the Bluetooth protocol is inconsistent with the standard, which makes the hardware interoperability, software interoperability, and software and hardware interoperability poor. (3) Software development is also difficult to provide a complete solution for Bluetooth applications, and cross-platform migration is difficult to achieve.
Although these problems are slowing down the speed of Bluetooth devices on the market, with the establishment of SIG new standards, it is expected that this unified data transmission method will be widely used. By then, hundreds of millions of computers and communication devices around the world will use Bluetooth Technology, it will bring a new era of wireless communication.
V. Specific networking solutions
According to the aforementioned Bluetooth routing mechanism, Figure 3 shows a schematic diagram of a specific application of a wireless office network. The Bluetooth gateway is connected to the LAN access interface through the RJ45 plug; the personal computer and various devices in the figure need to be equipped with a Bluetooth universal module or Bluetooth network card to make it Bluetooth. The maximum straight line between the Bluetooth gateway and each terminal cannot be greater than 100m, and a Bluetooth gateway can connect up to 7 devices with universal external modules. 
In the networking solution, the functions of the main components are as follows:
1. Bluetooth gateway (Jinou LLTR-1S)
* Adopt time division multiple access technology, support asynchronous data, support point-to-point, point-to-multipoint Bluetooth data communication;
* Have the interface and ability to communicate with the wired network and Bluetooth devices at the same time;
* Realize the address interpretation between Bluetooth address and IP address on the basis of security;
* Realize IP internet protocol and TCP transmission control protocol, which can complete the protocol conversion between Bluetooth protocol and TCP / IP;
* On the basis of the underlying protocol stack, the specific Bluetooth routing mechanism is implemented to solve the routing problem between Peak networks, in order to finally solve the communication problem of different units between different Peak networks in Bluetooth.
2. Network adapter (BlueBerry Bluetooth USB)
Installed on PCs and laptops inside the network to make the device Bluetooth.
3. In order to make the office equipment such as printers, projectors, scanners, etc. in the office have Bluetooth function, select Jinou's general Bluetooth module, which has serial port, USB and parallel port for selection.
6. Conclusion
The establishment of an office network using Bluetooth technology not only plays a role when the office conditions are not perfect, but also has unique advantages in temporarily adding or deleting office points and mobile office services. At present, there are still deficiencies in the application of Bluetooth technology, such as lack of channel compatibility, reliability and security, and it is impossible to achieve true "roaming", which is more prominent in the application of shared storage networks. However, with the development of Bluetooth technology, it will become more and more economical and practical to form an office wireless short-range network.
This paper proposes a Bluetooth wireless office network solution, which can be used to realize the wireless office of modern enterprises. Devices in the network can log in to the local area network or the Internet in the unit wirelessly, and each device can also file wirelessly. The sharing of resources saves the complicated connections between devices, greatly improves the office environment of people, and improves the degree of office automation of modern enterprises. At the same time, it can bring decision makers in all aspects of enterprise management, production and operation. Great convenience, making scheduling decisions more accurate, standardized and timely
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