WLAN is a wireless local area network, which combines the advantages of wireless communication technology and computer network, and uses wireless channel as the transmission medium to realize wireless network communication in a short distance.
The basis of WLAN is traditional wired LAN. It only realizes wireless communication through wireless access point (AP), wireless bridge, wireless network card and other devices on the basis of wired LAN.
WLAN has many features such as easy installation, easy expansion, easy maintenance, mobility, high speed, and use of open frequency bands. Enterprises, individuals, and operators have already recognized the advantages of WLAN in wireless data transmission. WLAN can be seamlessly integrated with Ethernet, which is widely used today, enabling users to access the Internet, conduct online transactions, and remotely work in a variety of applications. With the continuous expansion of application fields, various business applications have put forward higher requirements for WLAN, such as speed, security, QoS, and roaming. In addition, in addition to data transmission, WLAN is also expected to make breakthroughs in wireless voice. The following is a brief introduction to the current hot spots of WLAN development.
Rate
Bandwidth is the foundation of everything. The widely used WLAN devices are based on the 802.11b standard and have a maximum wireless rate of 11 Mbps. In fact, due to the wireless frame header overhead, access control, etc. of the WLAN standard, the rate that the user actually obtains 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. The IEEE 802.11n working group is currently developing a higher-speed WLAN standard that can increase the rate to 108/320 Mbps; 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 from wired network is that any wireless network card and access point can receive wireless signals. Therefore, the security of WLAN network has always been a hot topic of WLAN discussion. In addition to widely used SSID, ACL and WEP, in order to improve the security of WLAN networks, the recent 802.11i standard adopted by IEEE will have a profound impact on the security of WLAN networks.
The IEEE 802.11i standard combines user port authentication and device authentication in 802.1x to modify and standardize the MAC layer of the WLAN, and defines a strict encryption format and authentication mechanism to improve the security of the WLAN. The IEEE 802.11i standard mainly includes two contents: Wi-Fi Protected Access (WPA) (Wi-Fi Protected Access) technology and robust secure network RSN technology. The WPA technology uses the Temporary Key Integrity Protocol (TKIP) and algorithms 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 provides the function of quickly updating the key and solves the shortcoming of WEP vulnerability. Based on the 802.1x protocol and the Extensible Authentication Protocol (EAP), the RSN uses the advanced encryption standard AES to use dynamic authentication and encryption algorithms between access points and mobile devices for more powerful encryption and information integrity checks. .
3.QoS
Because WLAN currently follows the Ethernet sharing mechanism, there is almost no distinction between different types of services. In this way, for applications such as VoIP and video, which have high requirements on attributes such as delay, bandwidth, and packet loss rate, the necessary guarantee cannot be provided. Therefore, the IEEE has specially established 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 traditional wired LANs, which tagged packets and utilizes prioritized channel access functions for transmission. Supports 8 types of communication priority grading, and can directly implement mapping with RSVP priority protocols. HCF is a query access mechanism in which different transport streams are allocated to dedicated communication slots. These two mechanisms combine to maintain QoS control between the network and wireless users.
4. Roaming
In response to the problem of wireless LAN users roaming between access points, the IEEE working group has developed the 802.11f protocol, which elaborates the Inter-Access Point Protocol (IAPP), which is intended to provide users with inter-AP mobility. Features to meet user demand for mobility. Its main function is to facilitate the creation and maintenance of the extended service set ESS, to support the movement of 802.11 mobile terminals between APs, and to ensure that each mobile terminal has only one connection relationship with the AP at a certain moment.
5. Voice application
VoIP has been widely accepted by the public, and people can easily access the network through WLAN. The combination of these two advantages technologies has emerged as a VoWLAN application. Wi-Fi mobile phones are available now, but limited to WLAN coverage, mainly used within the enterprise, and may be used in the digital home field in the future. There are also some device manufacturers that are developing WLAN+GSM or CDMA dual-mode phones, which combines WLAN voice applications with mobile networks.
The development of WLAN technology is closely related to the application requirements. Users' requirements for the wide range of mobility and high bandwidth of the rate are constantly improving. Standard organizations and equipment manufacturers and operators are actively developing relevant standards and products and services to meet the requirements. User needs. On the one hand, the application of new standards and technologies to solve the existing technical problems and equipment defects; on the other hand, through the integration of other technologies to achieve complementary technical advantages, to achieve common development of various technologies.
WiMAX: The new wireless metropolitan area network1. Standard situation
The current WiMAX standard generally refers to the IEEE 802.16d standard adopted by the IEEE in June 2004, which covers the full version of IEEE 802.16 and IEEE 802.16a, including all LOS and NLOS bands (2-66 GHz) and 2-11 GHz. System implementation frameworks (Profiles). WiMAX technology can also be broadly understood as the IEEE 802.16 family of standards promoted by the current WiMAX (Worldwide Interoperability for Microwave Access) forum.
2. Advantages of WiMAX
The advantages of WiMAX are mainly reflected in the integration of the mobility and flexibility of Wi-Fi wireless access technology, and the high bandwidth characteristics and relatively ideal QoS quality of traditional cable-based broadband access technologies such as DSL and CableModem. . 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, which makes this technology not only capable of long-distance signal transmission and non-line-of-sight transmission capability through obstacles such as trees and buildings, but also has strong signal reflection and fault tolerance. At the same time, this modulation mode enables the service provider base station to adjust the bandwidth according to the strength of the signal to ensure a normal connection with the user.
WiMAX also provides deployment and configuration scalability, including flexible channel planning, enabling operators to flexibly plan channel bandwidth based on licensed or unlicensed band resources and continually upgrade the extended network based on user community conditions. For an operator with a 20MHz spectrum, it can be divided into two 10MHz channels or divided into four 5MHz channels.
WiMAX also provides QoS quality of service support for voice and low-latency video service applications, and enables operators to support both enterprise users using E1 type connectivity and home consumer users using DSL and other types of connectivity based on the same base station. For remote areas such as suburbs and rural areas, support for voice communications is available.
In addition, in order to protect user information security, especially to meet the needs of enterprise users for business application data security, WiMAX technology also provides privacy and encryption protection, and can ensure data transmission security through identity authentication and data encryption.
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 such as suburban and rural areas where DSL and CableModem services are effectively covered, or where traditional broadband access technologies are not easily deployed. 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 space.
The CPWG (ContribuTIontoServiceProvider Working Group) working group under the WiMAX Forum specifies the applications supported by the WiMAX network in the December 2004 WiMAX network specification requirements, which are divided into three applications: common IP applications, advanced IP applications. And non-IP applications.
(1) General IP application
Non-real-time IP applications such as FTP, e-mail, web browsing, remote access VPN, etc. should be supported. Ordinary services are characterized by best-effort service, that is, there is no definite QoS guarantee for these services.
(2) Advanced IP application
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), Targeting and presence triggering IP applications, manageable VPN services (based on client-side or network operators), and games. Managed IP services provide specific SLAs (ServiceLevelAgreements), including QoS. And support different billing strategies.
(3) Non-IP services
Compatible with the existing SMS (ShortMessageService) and MMS (MulTImediaMessage Service) services.
4. Development dynamics
The WiMAX Forum is a non-profit organization. Members include: broadband wireless access equipment manufacturers, component suppliers (chips, RF, antennas, software and test services, etc.) and service providers (operators, wireless ISPs). As of February 2005, its membership has exceeded 200. The goal of the WiMAX organization is to facilitate 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. WiMAX's relationship with IEEE 802.16 is similar to Wi-Fi and IEEE 802.11, providing "WiMAX-CerTIfied" certification labels for tested devices worldwide.
The WiMAX Forum has set up TWG (TechnicalWorkingGroup) and CWG (CerTIficationWorking Group) working groups.
TWG's mission is to develop application layer and network architecture specifications for future services and interoperability based on GlobalStandard's consistency and interoperability specifications.
The CWG's mission is primarily to manage consistency, interoperability and certification processes, and to be responsible for the quality of laboratory coordination and testing processes.
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