What is a Wireless LAN?

WLAN is the abbreviation of Wireless Local Area Network, which refers to the application of wireless communication technology to interconnect computer equipment to form a network system that can communicate with each other and realize resource sharing. The essential characteristic of wireless local area network is that it no longer uses communication cables to connect computers to the network, but connects them wirelessly, thereby making the construction of the network and the movement of terminals more flexible. ^[1]

It is a very convenient data transmission system. It uses radio frequency (RF) technology and uses electromagnetic waves to replace the old-style inconvenient twisted-pair copper wire (Coaxial) formed by a local area network. It communicates in the air to make wireless local area network. Lonergy uses a simple access architecture to allow users to use it to achieve the ideal state of "information on the go and convenient access to the world." ^[2]

Chinese name: Wireless local area network
Foreign name: Wireless Local Area Networks; WLAN
Technology: Radio frequency

Standard: IEEE802.11 / a / g / b / n / ac
Need equipment: Wireless network card, wireless router
Advantages: Flexibility and mobility

Introduction to WLAN

Before the wireless local area network WLAN was invented, if people wanted to communicate and communicate through the network, they must first use physical cables-copper stranded wires to establish an electronic operation path. In order to improve efficiency and speed, optical fiber was later invented. After the network has reached a certain scale, people have found that whether this wired network is constructed, disassembled, or relocated and rebuilt on the original basis, it is very difficult, and the cost and cost are very high. Came into being. ^[1]

WLAN started in 1997. In June of that year, the first wireless local area network standard IEEE802. 11 was officially promulgated and implemented, which provided a unified standard for wireless local area network technology, but the transmission rate at that time was only 1 ~ 2 Mbit / s. Subsequently, the IEEE committee began to formulate new WLAN standards, named IEEE802.lla and IEEE802.llb, respectively. The IEEE802.llb standard was first officially promulgated in September 1999, and its rate is 11 Mbit / s. The improved IEEE802.lla standard was officially promulgated at the end of 2001. Its transmission rate can reach 54 Mbit / s, which is almost 5 times that of the IEEE802.llb standard. Nevertheless, the application of WLAN has not really started, because the entire WLAN application environment is not mature. ^[1]

The true development of WLAN started from Intel's first launch of the Centrino processor with a WLAN wireless network card chip module in March 2003. Although the wireless network environment at that time was still very immature, the most developed United States was no exception. However, due to the bundled sales of Intel, coupled with the high performance and low power consumption of Centrino chips, many wireless network service providers see business opportunities. At the same time, 11 Mbit / s access rates are also available in general small local area networks. Carry out some daily applications, so wireless network service providers in various countries have started to provide access hotspots in public places (such as airports, hotels, cafes, etc.). In fact, some wireless access points (APs) are arranged to facilitate mobile business people. Go online. ^[1]

After more than two years of development, wireless network products and applications based on the IEEE802.llb standard have been quite mature, but after all, the 11 Mbit / s access rate is far from meeting the actual network application requirements. ^[1]

In June 2003, after more than two years of development and many improvements, a new standard compatible with the original IEEE802.llb standard and also providing 54 Mbit / s access rate-the efforts of IEEE802.llg in the IEEE Committee Officially released. ^[1]

Currently the most commonly used are 802.lln (fourth generation) and 802.1 llac (fifth generation) standards. They can work in both the 2.4 GHz and 5 GHz bands, and the transmission rate can reach 600 Mbit / s ( Theoretical value). But strictly speaking, only those that support 802.1llac are truly 5G. Nowadays, many routers that support 2.4G and 5G dual-frequency actually only support the fourth-generation wireless standard, which is 802.lln dual-frequency, and The cheapest route that really supports ac5 G is four or five hundred yuan or even thousands of yuan. ^[1]

Advantages and disadvantages of wireless local area networks

Advantages of wireless LAN

Flexibility and mobility. In a wired network, the placement of network equipment is limited by the network location, and a wireless local area network can access the network at any location within the coverage area of the wireless signal. Another great advantage of wireless local area networks is their mobility. Users connected to wireless local area networks can move and stay connected to the network at the same time. ^[3]

Easy installation. Wireless local area network can eliminate or minimize the workload of network wiring. Generally, as long as one or more access point devices are installed, a local area network covering the entire area can be established. ^[3]

(3) Easy network planning and adjustment. For wired networks, changes in office locations or network topology usually mean rebuilding the network. Rewiring is an expensive, time-consuming, wasteful, and trivial process. Wireless LAN can avoid or reduce the above situation. ^[3]

Easy fault location. Once a wired network has a physical failure, especially a network outage caused by a poor connection, it is often difficult to pinpoint it, and repairing the line requires a significant price. The wireless network is easy to locate the fault, and the network connection can be restored by simply replacing the faulty device. ^[3]

Easy to expand. There are multiple configuration methods for wireless local area networks, which can quickly expand from a small local area network with only a few users to a large network with thousands of users, and can provide features that wired networks such as "roaming" between nodes cannot achieve. Because of the many advantages of wireless local area network, its development is very rapid. In recent years, wireless local area networks have been widely used in enterprises, hospitals, shops, factories and schools. ^[3]

Insufficient wireless local area network

The shortcomings of wireless local area networks: While wireless local area networks can bring convenience and practicality to network users, there are also some shortcomings. The shortcomings of wireless local area networks are reflected in the following aspects: Performance. Wireless local area networks rely on radio waves for transmission. These radio waves are transmitted by wireless transmitting devices, and buildings, vehicles, trees and other obstacles may hinder the transmission of electromagnetic waves, so it will affect the performance of the network. rate. The transmission rate of wireless channels is much lower than that of wired channels. The maximum transmission rate of a wireless local area network is 1 Gbit / s, which is only suitable for personal terminals and small-scale network applications. (3) Security. In essence, radio waves do not require the establishment of a physical connection channel, and wireless signals are divergent. In theory, it is easy to monitor any signal in the radio wave broadcast range, causing communication information leakage. ^[3]

WLAN wireless local area network topology

The wireless local area network based on the IEEE802.11 standard allows wireless connection in the local area network environment using the 2.4GHz or 5GHz radio frequency band in the ISM band which does not need to be authorized. They are widely used, from homes to businesses to Internet access hotspots. ^[4]

Figure 1.Wireless LAN Simple Home Wireless LAN Simple Home Wireless WLAN: The most versatile and cheapest example of a home wireless local area network, a device acts as a firewall, router, switch, and wireless access point. These wireless routers can provide a wide range of functions, such as protecting your home network from outside intrusions. Allows to share a single IP address of an ISP (Internet Service Provider). Provides wired Ethernet services for 4 computers, but can also be expanded with another Ethernet switch or hub. Make a wireless access point for multiple wireless computers. Basic modules typically provide Wi-Fi for 2.4GHz 802.11b / g operation, while higher-end modules will provide dual-band Wi-Fi or high-speed MIMO performance. ^[3]

Dual-band access points provide 2.4GHz802.11b / g / n and 5.8GHz802.11a performance, while MIMO access points can use multiple radio frequencies in the 2.4GHz range to improve performance. Dual-band access points are essentially two access points in one and can provide two non-interfering frequencies at the same time, while newer MIMO devices increase speed in the 2.4GHz range or higher. The 2.4GHz range is often crowded and due to cost issues, manufacturers have avoided dual-band MIMO equipment. Dual-band devices do not have the highest performance or range, but allow you to operate in the relatively less crowded 5.8GHz range, and if two devices are in different bands, allow them to operate at full speed at the same time. Examples in home networks are uncommon. This topology is more expensive but provides more flexibility. Routers and wireless devices may not provide all the features that advanced users want. In this configuration, the cost of such an access point may exceed the price of a comparable router and AP all-in-one, due to the fact that there are fewer such products in the market because most people prefer a combination of features. Some people need higher end routers and switches because these devices have features such as bandwidth control, Gigabit Ethernet, and standard designs that allow them to have the flexibility they need. ^[3]

WLAN wireless bridging

Wireless bridging allows wireless connections between buildings when wired to Ethernet or a second redundant connection needs to be established for wired connections for backup. 802.11 devices are commonly used for this application as well as wireless fiber bridges. Basic 802.11 solutions are generally cheaper and do not require

Wireless local area network There is direct visibility between the antennas, but it is much slower than fiber solutions. 802.11 solutions typically operate in the range of 5 to 30 mbps, while fiber optic solutions operate in the range of 100 to 1000 mbps. The two bridges can operate at distances of more than 10 miles, and 802.11-based solutions can reach this distance without requiring a cable connection. However, the disadvantages of 802.11-based solutions are slow speed and interference, while fiber-optic solutions do not. The disadvantages of fiber optic solutions are the high price and the lack of visibility between the two locations. ^[3]

WLAN WLAN Medium WLAN

Mid-size businesses traditionally use a simple design that simply provides multiple access points to all facilities that require wireless coverage. This particular method is probably the most versatile because it has low entry costs, even if the number of access points exceeds a certain limit

Figure 2 Wireless LAN It becomes difficult to manage. Most of these wireless LANs allow you to roam between access points because they are configured in the same Ethernet subnet and SSID. From a management perspective, each access point and the interface connected to it are managed separately. In more advanced operations that support multiple virtual SSIDs, VLAN channels are used to connect access points to multiple subnets, but require an Ethernet connection with a manageable switch port. The switch in this case needs to be configured to support multiple VLANs on a single port. ^[3]

Although it is possible to configure multiple access points using a single template, managing the large number of access points can still become difficult when the firmware and configuration needs 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 can take turns to connect to a central user database such as Windows Active Directory. But even so, a RADIUS association needs to be established between each access point and each RADIUS server. If the number of access points is large, it will become complicated. ^[3]

WLAN WLAN Large WLAN

Switching wireless local area networks is the latest development in wireless networking. Simplified access points are controlled by several centralized wireless controllers. Data is transmitted and managed through centralized wireless controllers from manufacturers such as Cisco, ArubaNetworks, Symbol and TrapezeNetworks. The access point in this case has a simpler design to simplify complex operating systems, 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. To support multiple VLANs, the 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.

Figure 3 Wireless LAN From a management perspective, administrators only need to manage wireless LAN controllers that can take turns controlling hundreds of access points. These access points can use certain custom DHCP attributes to determine where the wireless controller is, and automatically connect to it as an extension of the controller. This greatly improves the scalability of switched wireless local area networks because the additional access points are plug and play in nature. To support multiple VLANs, the access point no longer needs a special VLAN tunnel port on the switch it connects to, and can use any old access port on any switch or even a manageable hub. VLAN data is encapsulated and sent to a central wireless controller, which handles a single high-speed multi-VLAN connection to the core network switch. Security management is also hardened, because all access control and authentication are handled in a centralized controller, not at each access point. Only the centralized WLC needs to connect to the RADIUS servers, which in turn connect to Active Directory in the example shown in Figure 6. ^[3]

Another benefit of switched WLANs is low-latency roaming. This allows latency-sensitive applications like VoIP and Citrix. Switching time can occur in approximately 50 milliseconds, which is usually not noticeable. Traditionally, each access point is independently configured with a wireless local area network with a switching time in the range of 1000 milliseconds, which will destroy phone calls and discard application sessions on wireless devices. The main disadvantage of switching wireless local area networks is the additional cost due to the additional cost of the wireless controller. But in large wireless LAN configurations, these additional costs are easily offset by manageability. ^[3]

Wireless networking requirements for wireless local area network

Because wireless local area networks need to support high-speed, bursty data services, indoor use also needs to address issues such as multipath fading and crosstalk between subnets. Specifically, wireless local area networks must implement the following technical requirements: ^[3]

Wireless local area network

1. Reliability: The system packet loss rate of the wireless local area network should be lower than 10 ^-5 , and the bit error rate should be lower than 10 ^-8 . ^[3]

2. Compatibility: For wireless local area networks used indoors, they should be compatible with existing wired local area networks in network operating systems and network software. ^[3]

3 Data rate: In order to meet the needs of LAN traffic, the data transmission rate of wireless LAN should be above 54Mbps. ^[3]

4 Communication confidentiality: Since data is transmitted in the air through wireless media, wireless local area networks must take effective measures at different levels to improve communication confidentiality and data security performance. ^[3]

5. Mobility: Supports all mobile networks or semi-mobile networks. ^[3]

6. Energy saving management: When there is no data transmission and reception, the site machine is in a dormant state, and then activated when there is data transmission and reception, so as to achieve the purpose of saving power consumption. ^[3]

7. Miniaturization and low price: This is the key to the popularity of wireless local area networks. ^[3]

8. Electromagnetic environment: Wireless local area network should consider the influence of electromagnetic on human body and surrounding environment. ^[3]

When setting up a wireless local area network, it is often necessary to carefully consider many detailed factors in order to successfully build a wireless local area network and ensure its high performance. ^[5]

1. When connecting to a remote LAN through a wireless LAN, the building where the remote LAN is located should be as visible as possible. If the wireless LAN is to pass through tall buildings or dense trees, the transmission performance of the established wireless LAN will be affected. After all, those obstacles will directly affect the normal transmission of wireless LAN data signals. ^[5]

2. When the distance between the remote network and the local LAN is relatively long, the network transmission bandwidth can be appropriately reduced to achieve the purpose of long-distance data transmission. If long-distance wireless transmission is needed, you may try to set up a wireless LAN relay relay in the middle. Stand so that Internet signals bypass obstacles. In the wireless local area network, in order to ensure that the maximum transmission bandwidth can be obtained when network signals are transmitted at short distances, several wireless bridges must be integrated with each other, and the antenna height of the wireless local area network will not be affected basically. ^[5]

3. It is also very important to set the antenna height of the wireless local area network properly. If the antenna height of the wireless local area network equipment is not set properly, relying solely on increasing the antenna gain or increasing the power amplification, the wireless transmission effect obtained will be very limited. Then you can consider arranging the antenna of the wireless node device on the most item level of the building, and use small antennas as much as possible to ensure the relative concentration of radio waves, which is beneficial to effectively avoid interference from other wireless local area network signals. ^[5]

4. Although the wireless LAN transmission uses frequency hopping technology, the frequency carrier of the Internet signal is difficult to detect. In this way, the secure transmission of the wireless Internet signal can only be performed when both parties have set the same network ID number wirelessly. If you want to further ensure the security of wireless LAN operation, you can also encrypt the wireless Internet signal. ^[5]

Wireless LAN networking mode

By combining several devices in WLAN, a multi-level, wireless and wired computer network can be established. Generally speaking, wireless LANs have two networking modes, one is a WLAN without a fixed base station, and the other is a WLAN with a fixed base station. ^[5]

A WLAN without a fixed base station is a self-contained network, which is mainly suitable for a peer-to-peer network formed between computers with wireless network cards installed. A WLAN with a fixed base station is similar to a mobile communication mechanism. A computer with a wireless network card is connected to the network through a base station (wireless AP or wireless router). This network is widely used, and is usually used to extend the coverage of a wired LAN or as a broadband Wireless Internet access. ^[5]

WLAN WLAN without fixed base station

A WLAN without a fixed base station is also called a wireless peer-to-peer network, which is the simplest type of wireless local area network structure. This WLAN structure without a fixed base station is a centerless topology. The communication relationship between the devices connected through the network is equal, but it is only suitable for a small number of computer wireless connection methods (usually 5 hosts). Or within the device). ^[5]

This networking mode does not require fixed facilities, it can be achieved by installing a wireless network card in each computer, so it is very suitable for the establishment of some temporary networks. ^[5]

WLAN WLAN with fixed base station WLAN

When the number of computer users on the network reaches a certain level, or when a stable wireless network platform needs to be established, an AP-centric networking mode is generally adopted. ^[5]

The AP-centric networking mode is also the most common wireless LAN mode. In this mode, an AP is required to act as a central station, and all sites' access to the network is controlled by the center. ^[5]

WLAN hardware equipment

Wireless local area network 1. Wireless network card. The role of the wireless network card is basically the same as the function of the network card in Ethernet. As an interface of the wireless local area network, it can realize the connection and communication between the clients of the wireless local area network. ^[3]

2. Wireless AP. AP is an abbreviation of Access Point. A wireless AP is an access point and a wireless gateway for a wireless local area network. Its role is similar to a hub in a wired network. ^[3]

3 Wireless antenna. When the network devices in the wireless network are far away, as the signal weakens, the transmission rate will decrease significantly so that the normal communication of the wireless network cannot be achieved. At this time, the received or transmitted signal must be enhanced by means of a wireless antenna. ^[3]

WLAN user management

The content of user management of wireless local area network includes the emphasis on the management of mobile phone user archives, change records and other data in mobile communications and the management of switch user data; user management in broadband ADSL networks emphasizes user authentication management and accounting. Fee management, of course, also includes the management of user data; in a distributed system, the establishment, deletion, permission setting, registration, connection, and accounting of users are emphasized. But all user management is nothing more than the system content such as system IP address allocation, user database management, user registration, user level management, user permission settings, user logs, and system working status monitoring. ^[4]

After the introduction of the new generation of the Internet protocol IPv6, the user management of wireless LAN mainly deals with the following aspects: ^[4]

IP WLAN IP address assignment

The wireless local area network uses a wireless link from the user to the wireless access point, so there is no problem of IP address allocation, but once it enters the access network, the AP that accesses the network will assign a temporary IP to the user. This IP will be used in the communication phase between the user and the network until the user is disconnected from the network and the IP is automatically released. There are two main methods for IP address allocation and management in IPv6 networks: passive allocation and active acquisition. Active acquisition is calculated through the related protocols of the IPv6 protocol cluster. It is mainly obtained through the specific algorithm of the network card MAC address. Passive allocation is Obtained by requesting a DHCPv6 server in the network. ^[4]

WLAN Database

The user database is set up to save the basic personnel information of the user, such as name, gender, etc. The purpose is to force the user to register with a real name and check whether the personal data entered by the user during registration is correct. When a user logs in to the website for the first time for user registration, the entire registration process can be completed only if the personal information entered is consistent with the content stored in the database, otherwise the registration cannot be successful. This part belongs to the application layer management and does not need to be changed much after being combined with IPv6. ^[4]

Wireless LAN Registration

User registration is the basis for classified and hierarchical management of end users to ensure the orderly operation of the system. The user registration information is the basis for the system to determine whether the visiting user is a registered user. To prevent ill-intentioned employees from registering by impersonation, the client IP address and user name, user password, and other personal information can be bundled and verified. After combining with IPv6, the IPv6 protocol itself provides good security, and we can make full use of some advantages of IPv6 to make user registration more complete. ^[4]

WLAN Login

When the terminal accesses the network, the network can automatically obtain the IP address of the visiting client, and compare the IP address with the record in the user registration database to determine whether the visitor is a registered user. If no information related to the client's IP address is found in the database, indicating that it is an unregistered terminal, then it is guided to perform user registration: If the IP address registration information exists in the user registration database, it indicates that the client has performed After registration, the user will be prompted to enter his or her profile name, password, etc., and then compared with the records in the user registration database to verify the user's password to confirm the user's identity. The identified user will be automatically assigned an identity by the system, and the user cannot obtain and change the identity information on the terminal whose lifetime can be controlled by the system. ^[4]

Wireless LAN level settings

Users usually have a clear and fixed job in the unit and organization, belonging to a certain department and group, and located at a certain administrative level. Users at different levels are set by the system administrator based on personnel data and user registration information. After this part is combined with IPv6, there is basically no change, that is, the access to the WLAN network in the next-generation all-IP network will not change much. ^[4]

Wireless LAN permission settings

In order to prevent users from unauthorized access and random information release activities, users must be restricted. Of course, this has nothing to do with the specific network protocol, so there is no change in the next generation IPv6 network. ^[4]

WLAN log

The user log is the first-hand information to record the click rate of the user activity statistics column and analyze and improve the utilization of the network. User logs are saved in the database, which is convenient for future statistical analysis. Using user log information, statistical analysis can be performed on information such as sites and columns browsed by users when they log in. This part belongs to the operation of the application layer. After the introduction of IPv6 technology, no change is needed. ^[4]

Wireless LAN Application

There are many implementation protocols for WLAN. The most famous and most widely used is Wi-Fi technology, which actually provides a technology that can interconnect various terminals with wireless to shield users. The differences between various terminals. ^[4]

In practical applications, the WLAN access method is very simple. Taking a home WLAN as an example, only a wireless access device-a router, a computer or terminal (mobile phone or PAD) with wireless functions, and a computer without wireless functions need only be Just plug in a wireless network card. With the above equipment, the specific operation is as follows: Use a router to connect the hotspot (other wireless networks that have been set up and within the receiving range) or wired network to the home, and configure routing according to the instructions provided by the network service provider. Place the receiving terminal within the coverage area (stable coverage of the WLAN is between 20 m and 50 m). Turn on the wireless function of the terminal and enter the user name and password given by the service provider to access the WLAN. ^[4]

The typical application scenarios of WLAN are as follows: ^[4]

(1) Between buildings: It is simple and cheap to build a network connection between buildings, instead of dedicated lines. ^[4]

Figure 4 Wireless LAN

(2) Catering and retail: The catering service industry can use wireless local area network products, which can input and transmit guests' order content to the kitchen and counter directly from the dining table. Retailers can use wireless LAN products to set up temporary checkout counters during promotions. ^[4]

(3) Medical treatment: Use a portable computer with a wireless local area network product to obtain real-time information. Medical staff can avoid delays in the treatment of injuries, unnecessary paperwork, delays in document circulation, and misdiagnosis. The quality of injury care. ^[4]

(4) Enterprise: When employees in the enterprise use wireless local area network products, no matter where they have wireless local area network products in the office, they can freely send emails, share files and browse the Internet. ^[4]

(5) Warehousing management: Inventory of general warehousing personnel, the latest information can be immediately entered into the computer warehousing system through the application of wireless networks. ^[4]

(6) Container terminal: The bridge crane in general container terminal can transfer real-time information back to the office when the container is mobilized to facilitate the related operations. ^[4]

(7) Surveillance system: It is generally located in a remote place and needs to be monitored. Due to the difficulty of wiring, the remote image can be transmitted back to the main control station through the wireless network. ^[4]

(8) Exhibition venues: such as general electronics exhibitions and computer exhibitions. Due to the extremely high network requirements and the wiring will make the venue look messy, if you can use wireless networks, it is the best choice. ^[4]