Simple home wireless LAN: The most common and cheapest example of home wireless LAN, as shown in figure 1, one device acts as a firewall, router, switch and wireless access point. These wireless routers can provide a wide range of functions, such as protecting the home network from external intrusion. Allow * * * to enjoy the single IP address of ISP. It can provide wired Ethernet service for four computers, but it can also be extended by another Ethernet switch or hub. Create wireless access points for multiple wireless computers. Generally speaking, the basic module will provide Wi-Fi with 2.4GHz802. 1 1b/g operation, while the higher-end module will provide dual-band Wi-Fi or high-speed MIMO performance. Dual-band access points provide 2.4GHz802. 1 1b/g and 5.3GHz802. 1 1a performance, while MIMO access points can use multiple radio frequencies in the range of 2.4GHz to improve performance. Dual-band access point is essentially a combination of two access points, which can provide two frequencies that do not interfere with each other at the same time, while the updated MIMO equipment improves the speed in the range of 2.4GHz or higher. The 2.4GHz range is usually crowded, and manufacturers avoid using dual-band MIMO equipment due to cost problems. Dual-band devices do not have the highest performance or range, but they allow you to work in the relatively less crowded 5.3GHz range. If two devices are in different frequency bands, they are allowed to work at full speed at the same time. Examples in home networks are not common. This topology is more expensive, but it provides greater flexibility. Routers and wireless devices may not provide all the functions required by advanced users. Under this configuration, the cost of this access point may exceed the price of a comparable router and AP integrated machine, because there are few such products on the market, because most people like to combine functions. Some people need higher terminal routers and switches, because these devices have the characteristics of bandwidth control and Gigabit Ethernet, and have standard design, which allows them to have the required flexibility. WLAN
Wireless bridge: When wired connection is too expensive or a second redundant connection needs to be established as a backup, wireless bridge allows wireless connection between buildings. 802. 1 1 devices are commonly used for this application and wireless optical fiber bridges. 802. The basic scheme of11is generally cheaper, and does not require direct vision between antennas, but it is much slower than the optical fiber scheme. 802. 1 1 solutions usually work in the range of 5 to 30mbps, while optical fiber solutions work in the range of 100 to 1000mbps. The running distance of these two bridges can exceed 10 miles, and the solution based on 802. 1 1 can reach this distance without cable connection. However, the scheme based on 802. 1 1 has the disadvantages of slow speed and great interference, while the optical fiber scheme will not. The disadvantage of the optical fiber scheme is that it is expensive and there is no direct line of sight between the two locations. WLAN
Medium-sized wireless LAN: Medium-sized enterprises have traditionally used a simple design, and they only need to provide multiple access points for all facilities that need wireless coverage. This particular method is probably the most common, because its entry cost is very low, although once the number of access points exceeds a certain limit, it becomes difficult to manage. Most wireless LANs allow you to roam between access points because they are configured in the same Ethernet subnet and SSID. From the management point of view, each access point and its connected interfaces are managed separately. In more advanced operations that support multiple virtual SSID, VLAN channels are used to connect access points to multiple subnets, but Ethernet connections need to have manageable switching ports. In this case, the switch needs to be configured to support multiple VLAN on a single port. Although a template can be used to configure multiple access points, it will still become difficult to manage a large number of access points when firmware and configuration need to be upgraded. From a security perspective, each access point must be configured to handle its own access control and authentication. RADIUS servers make this task easier because access points can delegate access control and authentication to centralized RADIUS servers, which in turn can connect to central user databases, such as Windows Active Directory. Even so, it is still necessary to establish a RADIUS association between each access point and each RADIUS server, which will become very complicated if there are many access points. Large switched WLAN: Switched WLAN is the latest development of wireless network, and the simplified access point is controlled by several centralized wireless controllers. Data is transmitted and managed by centralized wireless controllers of Cisco, ArubaNetworks, Symbol and TrapezeNetworks. In this case, the access point has a simple design that simplifies the complex operating system, and more complex logic is embedded in the wireless controller. Access points are usually not physically connected to the wireless controller, but they are logically switched and routed through the wireless controller. In order to support multi-VLAN, data is encapsulated in a tunnel in some form, so even if the devices are in different subnets, there is a direct logical connection from the access point to the wireless controller. WLAN
From the management point of view, administrators only need to manage wireless LAN controllers that can control hundreds of access points in turn. These access points can use some custom DHCP attributes to determine the location of the wireless controller and automatically connect to it to become an extension of the controller. This greatly improves the scalability of switched WLAN, because the additional access points are plug-and-play in nature. In order to support multiple VLANs, the access point no longer needs the special VLAN tunnel port on the switch it is connected to, and can use any old-fashioned access port on any switch, even the hub that is easy to manage. VLAN data is encapsulated and sent to the central wireless controller, which handles a single high-speed multi-VLAN connection to the core network switch. Security management has also been strengthened, because all access control and authentication are handled on the central controller, not on each access point. In the example shown in Figure 6, only the centralized wireless controller needs to be connected to the RADIUS server, and the RADIUS server is connected to the active directory. Another benefit of switching WLAN is low delay roaming. This allows delay-sensitive applications such as VoIP and Citrix. The switching time will occur in about 50 milliseconds, which is usually not obvious. The traditional wireless LAN with independent configuration of each access point has a switching time in the range of 1000 milliseconds, which will destroy the telephone call and discard the application session on the wireless device. The main disadvantage of switching WLAN is the extra cost due to the extra cost of wireless controller. However, in a large-scale WLAN configuration, these additional costs are easily offset by manageability. Application of WLAN: It is simple and cheap to establish network connection between buildings instead of dedicated lines. Catering retail: WLAN products can be used in catering service industry, and the ordering contents of guests can be directly input from the dining table and transmitted to the kitchen and counter. When retailers promote sales, they can use WLAN products to set up temporary checkout counters. Medical treatment: The use of portable computers with wireless LAN products to obtain real-time information can help medical staff avoid delaying the treatment of the wounded, unnecessary paperwork, delaying the circulation of documents and misdiagnosis, and improve the quality of care for the wounded. Enterprise: When employees use WLAN products, they can send emails, share files and browse the Internet at will, no matter where they are in the office. Warehouse management: General warehouse personnel can immediately input the latest data into the computer warehouse system through the application of wireless network. Container terminal: The bridge crane in general container terminal can transmit real-time information back to the office when transferring containers, which is convenient for related operations. Monitoring system: Generally, remote places that need to be monitored can send remote images back to the main control station through wireless network due to wiring difficulties. Exhibition venue: For example, general electronic exhibitions and computer exhibitions, because of the high network demand and messy wiring, it is a good choice if you can use wireless network. WLAN
Advantages of WLAN: (1) Flexibility and mobility. In wired network, the location of network equipment is limited by the location of the network, while wireless LAN can access the network anywhere within the coverage of wireless signals. Another biggest advantage of WLAN is mobility. Users connected to WLAN can stay connected to the network while moving. (2) Convenient installation. Wireless LAN can avoid or minimize the workload of network wiring. Usually, as long as one or more access point devices are installed, a local area network covering the whole area can be established. (3) It is convenient for network planning and adjustment. For wired networks, the change of office location or network topology usually means the reconstruction of the network. Reconnecting is an expensive, time-consuming, wasteful and trivial process, and WLAN can avoid or reduce the above situation. (4) Fault location is easy. It is often difficult to find the physical faults of wired networks, especially the network interruption caused by poor line connection, which will cost a lot to repair the lines. Wireless network is easy to locate faults, and network connection can be restored only by replacing faulty equipment. (5) Easy to expand. Wireless local area network (WLAN) has a variety of configurations, which can rapidly expand from a small LAN with only a few users to a large network with thousands of users, and can provide functions that wired networks cannot achieve, such as roaming between nodes. Due to the above advantages, wireless local area network has developed very rapidly. In recent years, WLAN has been widely used in enterprises, hospitals, shops, factories and schools. WLAN
Disadvantages of WLAN: WLAN can bring convenience and practicality to network users, but it also has some shortcomings. The disadvantages of WLAN are: (1) performance. Wireless LAN is transmitted by radio waves. These radio waves are transmitted by wireless transmitters, and obstacles such as buildings, vehicles and trees may hinder the transmission of electromagnetic waves, thus affecting the performance of the network. (2) speed. The transmission rate of wireless channel is much lower than that of wired channel. At present, the maximum transmission rate of WLAN is 150Mbit/s, which is only suitable for personal terminals and small-scale network applications. (3) Safety. In essence, radio waves do not need to establish a physical connection channel, and wireless signals are divergent. Theoretically, it is easy to monitor any signal within the broadcast range of radio waves, resulting in communication information leakage.
Edit the technical requirements of this paragraph.
Because WLAN needs to support high-speed and burst data services, it also needs to solve the problems of multipath fading and crosstalk between subnets when it is used indoors. Specifically, WLAN must meet the following technical requirements: WLAN
(1) Reliability: The system packet loss rate of WLAN should be lower than 10-5, and the bit error rate should be lower than 10-8. (2) Compatibility: For indoor wireless LAN, the network operating system and network software should be as compatible as possible with the existing wired LAN. (3) Data rate: In order to meet the needs of LAN traffic, the data transmission rate of WLAN should be above 1Mbps. (4) Communication security: Because data is transmitted in the air through wireless media, WLAN must take effective measures at different levels to improve communication security and data security. (5) Mobility: Full mobile network or semi-mobile network is supported. (6) Energy-saving management: when there is no data transmission and reception, make the site machine in a dormant state, and then activate it when there is data transmission and reception, so as to achieve the purpose of saving power consumption. (7) Miniaturization and low price: This is the key to the popularization of WLAN. (8) Electromagnetic environment: WLAN should consider the influence of electromagnetism on human body and surrounding environment.
Edit the hardware devices in this paragraph.
(1) wireless network card. The function of wireless network card is basically the same as that of Ethernet card. As the interface of WLAN, it can realize the connection and communication between WLAN clients. WLAN
(2) wireless AP. AP is the abbreviation of access point, and wireless AP is the access point and wireless gateway of wireless LAN, similar to the hub in wired network. (3) wireless antenna. When the network devices in the wireless network are far apart, with the weakening of the signal, the transmission rate will drop obviously, thus the normal communication of the wireless network cannot be realized. At this time, the received or transmitted signal will be enhanced by the wireless antenna.
Edit this open source project.
Using the open source software GNU Radio, BBN Technologies Internet Work Research BBN-BBN Technologies Internet Work Research Adroit project, 802.6438+05438+0 code was written under the sponsorship of DARPA. GNU Radio is a free software development tool suite. It provides signal operation and processing module, which can be used to realize software radio on low-cost RF hardware and general microprocessor which are easy to manufacture. This suite is widely used by amateurs, academic institutions and commercial organizations to research and build wireless communication systems. The application of GNU Radio is mainly written in Python programming language. WLAN
But its core signal processing module is built on the microprocessor of floating-point operation with C++. Therefore, developers can simply and quickly build a real-time, high-capacity wireless communication system. Although its main function is not an emulator, GNU Radio supports the research of signal processing algorithm for pre-stored and (signal generator) generated data without RF hardware components.
Edit this spread spectrum technology.