WLAN is a wireless local area network, which combines the advantages of wireless communication technology and computer networks, and uses wireless channels as a transmission medium to achieve wireless network communication in a short distance.
The basis of the wireless local area network is still the traditional wired local area network. It is based on the wired local area network to enable wireless communication through wireless access points (AP), wireless bridges, wireless network cards and other devices.
WLAN has many features such as easy installation, easy expansion, easy maintenance, mobility, high speed, and the use of open frequency bands. Both enterprises, individuals, and operators have recognized the advantages of WLAN in wireless data transmission. WLAN can be seamlessly combined with the widely used Ethernet, allowing users to access the Internet, conduct online transactions, remote office and other applications. With the continuous expansion of application fields, various business applications have put forward higher requirements for WLAN, such as speed, security, QoS, roaming and so on. In addition to data transmission, WLAN is also expected to make breakthroughs in wireless voice. The following briefly introduces the current hotspots of WLAN development.
1. Rate
Bandwidth is the foundation of all business. Currently widely used WLAN equipment is based on the 802.11b standard, the highest wireless rate can reach 11Mbps. In fact, due to the wireless frame header overhead and access control of the WLAN standard, the rate that users really get can only reach about half of the highest rate. The wireless interface speed of 802.11a and 802.11g devices is 54Mbps, and the actual throughput is only about 30Mbps. At present, the IEEE 802.11n working group is working on a higher rate WLAN standard that can increase the rate to 108 / 320Mbps; and further improve its management overhead and efficiency to enhance WLAN performance.
2. Security
WLAN realizes data communication through wireless signal transmission. The biggest difference with wired networks is that any wireless network card and access point can receive wireless signals. Therefore, the security of WLAN networks has always been a hot topic in WLAN discussions. In addition to the widely used SSID, ACL, and WEP, in order to improve the security of WLAN networks, the recent 802.11i standard passed by IEEE will have a profound impact on the security of WLAN networks.
The IEEE802.11i standard combines user port authentication and device authentication in 802.1x to modify and standardize the WLAN MAC layer, and defines strict encryption formats and authentication mechanisms to improve WLAN security. The IEEE802.11i standard mainly includes two contents: Wi-Fi Protected Access WPA (Wi-Fi Protected Access) technology and robust security network RSN technology. WPA technology uses Temporary Key Integrity Protocol (TKIP) and algorithm to improve the security of WEP. Like WEP, TKIP is also based on RC4 encryption, but the method of creating a key is different. It can provide a function of quickly updating the key, which solves the weakness of WEP's vulnerability. RSN is based on the 802.1x protocol and the Extensible Authentication Protocol EAP, uses advanced encryption standard AES, and uses dynamic authentication and encryption algorithms between access points and mobile devices to implement stronger encryption and information integrity checks .
3.QoS
Because WLAN currently follows the Ethernet sharing mechanism, it makes almost no distinction between different types of services. In this way, for applications such as VoIP and video that have high requirements on attributes such as delay, bandwidth, and packet loss rate, they cannot provide the necessary guarantees. Therefore, IEEE specially set up the 802.11e task group to refine the MAC layer of 802.11 to improve QoS. Two schemes are defined: enhanced distributed channel access (EDCA) and hybrid coordination function (HCF). EDCA is an extension of the queuing mechanism of the traditional wired LAN, marking the data packets and using prioritized channel access functions for transmission. Support 8 types of communication priority grading, can directly realize the mapping with RSVP priority protocol. HCF is a query access mechanism. In use, different transport streams are allocated to dedicated communication slots. The combination of these two mechanisms can maintain QoS control between the network and wireless users.
4. Roaming
In response to the problem of roaming between wireless LAN users between access points, the IEEE working group formulated the 802.11f protocol, which elaborated on the internal access point protocol IAPP (Inter-AccessPoint Protocol). The IAPP protocol is designed to provide users with mobility between APs. Functions to meet users' needs for mobility. Its main function is to facilitate the creation and maintenance of the extended service set ESS, support the movement of 802.11 mobile terminals between APs, and ensure that each mobile terminal has only one connection relationship with the AP at a certain time.
5. Voice application
At present, VoIP has been generally accepted by the public, and people can easily access the network through WLAN. The combination of these two advantageous technologies has led to the application of VoWLAN. Wi-Fi mobile phones are currently available, but they are limited to the coverage of WLANs and are mainly used within enterprises. In the future, they may be used in the digital home field. There are also some equipment manufacturers that are developing WLAN + GSM or CDMA dual-mode phones, making WLAN voice applications and mobile networks organically combined.
The development of WLAN technology is closely related to the application requirements. The users' requirements for the wide range of mobile and high bandwidth are constantly increasing. Standard organizations and equipment manufacturers and operators are actively developing related standards and products and services to meet User needs. On the one hand, the application of new standards and technologies to solve the current technical problems and equipment defects; on the other hand, through the integration of other technologies to achieve complementary technological advantages, to achieve the common development of various technologies.
WiMAX: the cutting-edge of wireless metropolitan area network
1. Standard Situation
The current WiMAX standard usually refers to the IEEE802.16d standard passed by IEEE in June 2004 and is a complete version covering IEEE802.16 and IEEE802.16a, including all LOS and NLOS frequency bands (2-66GHz) and 2-11GHz. System implementation framework (Profiles). WiMAX technology can also be broadly understood as the IEEE 802.16 series of standards promoted by the current WiMAX (Worldwide Interoperability for Microwave Access) forum.
2. Advantages of WiMAX
The advantage of WiMAX is that this technology integrates the mobility and flexibility of Wi-Fi wireless access technology, and the high bandwidth characteristics and relatively ideal QoS service quality of traditional cable-based broadband access technologies such as DSL and CableModem. . Among them, the most outstanding performance is its ideal non-line-of-sight transmission characteristics, flexible deployment and configuration scalability, excellent QoS service quality and strong security.
WiMAX is based on a dynamic adaptive signal modulation mode, so that this technology not only has long-distance signal transmission capabilities and non-line-of-sight transmission capabilities through obstacles such as trees and buildings, but also has strong signal reflection fault tolerance. At the same time, this modulation mode also enables the service provider base station to adjust the bandwidth according to the signal strength to ensure the normal connection with the user
WiMAX also provides flexibility in deployment and configuration, including flexible channel planning, allowing operators to flexibly plan channel bandwidth based on their own licensed or unlicensed band resources, and continuously upgrade and expand the network based on user group conditions. For an operator with a 20MHz spectrum, it can be divided into two 10MHz channels or four 5MHz channels.
WiMAX also provides QoS service quality support for voice and low-latency video service applications, and enables operators to support both enterprise users using E1 type connections and household consumer users using DSL and other types of connections based on the same base station. For remote areas such as suburbs and rural areas, it can provide support for voice communications.
In addition, in order to protect user information security, especially to meet the needs of business users for business application data security, WiMAX technology also provides privacy and encryption protection, through identity authentication and data encryption to ensure data transmission security.
3. Application
As a wireless LAN technology for the last-mile access field, WiMAX can be widely used in multiple broadband-related fields. Especially in areas where suburban and rural areas, such as DSL and CableModem services are not effectively covered, or where it is not convenient to deploy traditional broadband access technologies. In this case, WiMAX will become an advantageous broadband access option, and is expected to promote the deployment of 802.11 wireless hotspots and wireless LANs in the home or small office area.
The CPWG (ContribuTIontoServiceProvider Working Group) working group under the WiMAX Forum stipulated the applications supported by the WiMAX network in the WiMAX network specification requirements in December 2004, which are divided into three applications, namely: ordinary IP applications, advanced IP applications And non-IP applications.
(1) Common IP application
Should support non-real-time IP applications, such as FTP, e-mail, Web browsing, remote access VPN, etc. The characteristics of ordinary services are best-effort services, that is, there is no definite QoS guarantee for these services.
(2) Advanced IP applications
Supports all quasi-real-time applications, such as audio / video (A / V) streaming, VoIP, multimedia IP conferencing, IMS (IP multimedia subsystem) applications, MBS (multicast and broadcast services), PTT (Push-to-Talk), Location and presence trigger IP applications, manageable VPN services (client-based or provided by network operators), and games. Manageable IP services provide specific SLA (ServiceLevel Agreements), including QoS. And support different billing strategies.
(3) Non-IP services
Compatible with the existing SMS (ShortMessageService) and MMS (MulTImediaMessage Service) services.
4. Development Trend
The WiMAX Forum is a non-profit organization. Members include: Broadband wireless access equipment manufacturers, component suppliers (chips, radio frequency, antennas, software and test services, etc.) and service providers (operators, wireless ISPs). As of February 2005, its members have exceeded 200. The goal of the WiMAX organization is to promote the large-scale deployment of broadband wireless access networks based on the IEEE 802.16 standard by ensuring compatibility and interoperability between broadband wireless access devices. The relationship between WiMAX and IEEE802.16 is similar to Wi-Fi and IEEE 802.11, and provides "WiMAX-CerTIfied" certification labels for devices that pass the test worldwide.
WiMAX Forum has set up TWG (TechnicalWorkingGroup) and CWG (CerTIficationWorking Group) working groups.
The main tasks of the TWG are to develop consistency and interoperability specifications based on Global Standard, and to develop application layer and network architecture specifications for future services and interoperability.
The main tasks of the CWG are to manage the process of consistency, interoperability and certification, and to be responsible for the quality of laboratory coordination and testing processes.
Steel Miniature Weighing Sensor
Steel Miniature Weighing Sensor,Load Cells For Weighing,Weight Indicator Load Cell,Weight Cell Sensor
Xiaogan Yueneng Electronic Technology Co., Ltd. , https://www.xgsensor.com