IEEE 802.11b standard brief analysis
(Author: Li Wei, 2001 at 09:44 on February 14)
In the past, the wireless local area network has slowed slowly, and it is difficult to promote application, mainly due to low transmission rate, high cost, and a limited product line, and many products cannot be compatible with each other. For example, only 1 to 2Mb / s of the previous wireless LAN, and many applications are also designed according to the 10MB / s Ethernet rate, limiting the application type of wireless products. The key to the current high-speed data business and multimedia business, wireless local area networks are the development of high-speed new standards, as well as the emergence of 10MB / s even higher rates based on this standard. IEEE 802.11b fundamentally changed the design and application status of wireless LANs, meeting people to achieve uninterrupted mobile office in a certain region, create a free space for us. ■ 802.11B Standard Introduction IEEE 802.11b wireless LAN has a bandwidth of 11Mbps, 5 times faster than the IEEE 802.11 standard just approved two years ago, expanding the application area of Wireless LAN. In addition, 5.5Mbps, 2 Mbps, and 1 Mbps bandwidth can also be used according to the actual situation. The actual operating speed is around 5MB / s, which is almost at the same level of the same level with the ordinary 10Base-T specification. As the company's internal facilities, you can basically meet the requirements. IEEE 802.11b uses an open 2.4GB band, which is available without application. It can be used as a supplement to the wired network, and can also be independently assembled, so that the network users get rid of the linkage of the network cable to achieve true mobile applications. IEEE 802.11B Wireless LANs is similar to the principles of IEEE 802.3 Ethernet we are familiar with, all of which use carrier listening to control the transmission of information in the network. The difference is that Ethernet uses CSMA / CD (carrier listening / conflict detection) technology. All workstations on the network are listening to information transmission in the network. When the network is discovered, they issued their own information, such as answering the same It can only have a workstation to grab the right, and the rest of the workstation needs to continue. If there are two or more workstations simultaneously send a message, a conflict occurs in the network, and these conflict information will be lost after conflict, and the workstations will continue to snattle. The 802.11b wireless LAN has introduced conflict avoidance technology, thereby avoiding the occurrence of conflicts in the network, which can greatly improve network efficiency. IEEE 802.11b advantages
Function advantage speed 2.4GHz Direct sequence spread spectrum radio provides a data transfer rate of up to 11Mbps, without linear propagation dynamic rate conversion When the RF condition is deteriorated, reduce the data transmission rate of 5.5Mbps, 2Mbps and 1Mbps range 802.11b support The range of meters (300 meters outdoors; in the office environment is 100 meters) Reliability and Ethernet Similar connection protocols and packet confirmation provide reliable data transfer and network bandwidth effective use of interoperability with The previous standard is that 802.11b only allows a standard signal transmission technology. WECA will pass the interoperability power management 802.11b network interface card of the product to sleep mode, and the access point is built to the customer, extending the battery life roaming support of the laptop, when the user moves between the user, Allow seamless connection between the access points to load the access point for the connection and connection to improve performance (for example, when the current access point traffic is more crowd, or when a low quality signal) can be scalable. Access points can be locally located in the valid usage range to support hundreds of users at the same time voice and data support security built-in authentication and encryption ■ 802.11b basic operation mode 802.11b The operation mode is basically divided into two: point-to-point mode and Basic mode, as shown in Figure 1. Point-to-point mode refers to a communication method between wireless network cards and wireless network cards. As long as the PC is plugged in with another wireless network card, it is a convenient connection to a small wireless network, up to 256 PCs. The basic mode refers to a communication method when a wireless network scale expansion or wireless and wired network, which is the most common way of 802.11b. At this point, PCs inserted with the wireless network card need to be connected to another PC by the access point. The access point is responsible for the management of band management and roaming, and an access point can connect up to 1024 PCs (wireless network cards). When the wireless network node is amplified, the network access speed will slow down with the range expansion and the increase in nodes, and the add access point can effectively control and manage the bandwidth and frequency band. Wireless networks need to interconnect with wired networks, or wireless network nodes need to connect to and access to resources and servers, access points can be used as a bridge between wireless and cable networks. ■ Typical Solutions 802.11B 802.11B Wireless LAN Due to its convenience and scalability, it is especially suitable for small office environment and home networks. In an indoor environment, there are different types of solutions for different actual situations. Supreme solutions are the simplest application, as long as you install a wireless network card for each computer, you can access each other. If you need to connect to a wired network, you can install a cable network card for one of the computers. The rest of the wireless network uses this computer as a gateway, access a wired network or shared printer. However, the peer solution is a point-to-point scheme, and the computer in the network can only pass information one to each other, and cannot be multi-point access. If you want to implement an interworking function like a wired local area, you must use the access point. Single Point Solution Access Point is equivalent to a hub in a wired network. The wireless access point can connect the peripheral wireless network terminal to form a star network structure, and simultaneously connect to the wired network through the 10BASE-T port, so that the terminal of the entire wireless network can access the resources of the wired network and access the Internet via the router. 802.11b application
