Application of 802.1x Wireless Access
8.1 Introduction to WLAN
8.2 References
8.3 Availability 8.4 Principles 8.5 Applications 8.6 Impact
8.7 Terms and Abbreviations
8.1 Introduction to WLAN
Definition
A wireless local area network (WLAN) links two or more devices by using some wireless distribution method. It connects the devices such as PCs based on 802.11a, 802.11b, 802.11g, or 802.11n, the various versions of IEEE 802.11 (Wi-Fi), to form a resource-sharing
communications network. Radio waves are the media of data transmission on a WLAN.
Usually, cables are used on the backbone layer of a WLAN, and users access the WLAN from one or more wireless access points (WAPs). WLANs are popular on the campus and in the business centers, airports, and other public areas. The primary advantage of WLANs is that terminals such as computers can access a network through a wireless medium rather than a connected cable, which facilitates the network construction and gives users mobility to move around.
The WLAN feature includes AP management, RF management, Service Set Management (ESS profile), configuration auto-provisioning management, centralized BSSID management, load balancing, WLAN STA roaming, WLAN security, and QoS.
WLAN basics
Currently, the primary WLAN Wi-Fi access standards include IEEE 802.11a, 802.11b, 802.11g, and 802.11n.
8 WLAN
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Issue 01 (2010-06-25) A Wi-Fi-enabled device such as a mobile phone, laptop, or PDA can connect to the Internet when within range of a wireless network connected to the Internet. A Wi-Fi network uses the public channel provided for the equipment such as cordless telephones.
Once a hotspot is connected to the high-speed Internet, a Wi-Fi network can be set up within hundreds of meters around the hotspot.
Wi-Fi signals can be transmitted within only a radium of hundreds of meters but its rate can reach tens of megabits per second. The latest version of IEEE 802.11n supports the transmission rate of hundreds of megabits per second and the coverage of signals can be expanded to several square kilometers. This greatly improves the mobility provided for users. The architecture of a Wi-Fi network is very simple. Manufacturers deploy hotspots at airports, bus stations, coffee bars, libraries, and other densely populated places. To access the Internet at a high speed, users only need to take the equipment that supports Wi-Fi to receive signals in these areas.
Compared with other wireless access technologies, Worldwide Interoperability for Microwave Access (WiMax) features longer transmission radius, and the transmission distance can reach 50 kilometers; the cost of construction, however, is relatively high because big stations need to be deployed to support WiMax. WiMax can transmit data between Wi-Fi hotspots, but it cannot take the place of cost-effective and flexible Wi-Fi in homes and offices. In a word, WiMax uses the licensed or unlicensed spectrum to serve in metropolitan area networks (MANs), whereas Wi-Fi uses the unlicensed spectrum to serve in local area networks (LANs). As a complement to each other, WiMax and Wi-Fi provide a complete MAN/LAN solution.
3G access is another WAN technology. The same as WiMax, 3G access requires the support of big base stations. It provides seamless coverage in the downtown and suburbs so that users can use the services provided by the system everywhere.
Among the three wireless access technologies, Wi-Fi is relatively mature and its
development is quite fast. It can be used together with WiMax and 3G access in wireless access.
WLAN network architecture
The Control And Provisioning of Wireless Access Points (CAPWAP) working group of the Internet Engineering Task Force (IETF) researches on the solution to large-scale WLANs. This working group defines three WLAN architectures after a research on the popular WLAN solutions. They are autonomous WLAN architecture, centralized WLAN architecture, and distributed WLAN architecture. The distributed WLAN architecture is not described in this document because no network devices are required for this architecture.
A conventional WLAN usually adopts the autonomous architecture, which is also called the fat access point (AP) mode. In this mode, an AP carries out all the functions defined in IEEE 802.11, and every AP in the WLAN needs to be configured, managed,
monitored, and controlled. Because a large-scale WLAN consists of hundreds of APs, the configuration and management of all the APs in the WLAN inflict a heavy load on the network management system. On the other hand, APs are independent of each other, which makes the dynamic management of network-wide wireless resources difficult. In addition, APs are often installed in unsafe places to cover wide areas. Thus, if APs are stolen, the configurations statically stored on the APs will leak. How to deny illegal APs the access is also a great challenge to the autonomous WLAN architecture. To solve all the preceding problems of the autonomous WLAN architecture, the centralized WLAN architecture emerges, giving solutions to the network management, security, resource management, and interoperability in large-scale WLANs. The centralized WLAN architecture is also called the fit AP mode.
Figure 8-1 Centralized WLAN architecture
As shown in Figure 8-1, an access controller (AC) is added in the centralized
architecture compared with the autonomous architecture. An AC can be considered as a group of logical devices, which implement network management, monitoring, dynamic configuration, and Authentication, Authorization, and Accounting (AAA). The wireless termination points (WTPs) shown in this figure are different from the APs defined in IEEE 802.11. APs perform all the functions defined in IEEE 802.11, whereas WTPs perform only some of these functions. Therefore, WTPs are considered as lightweight APs. The connection between an AC and a WTP can be a direct connection, an L2 switched connection, or an L3 routed connection. Through an L3 routed connection, a WTP can access an AC on an IP network, which makes the WTP deployment more flexible and implements seamless Layer 3 roaming. For this reason, L3 routed connections are widely used.
In the centralized WLAN architecture, the CAPWAP protocol is applied to endow the AC with WTP management capabilities. Most of the CAPWAP functions reside in the AC (except for the function defined in IEEE 802.11, the CAPWAP working group defines the following CAPWAP functions: RF monitoring, RF configuration, WTP configuration, WTP firmware loading, network-wide STA state information database, mutual authentication between network entities, for example AC and WTP authentication in a centralized WLAN architecture). The physical layer functions defined in IEEE 802.11 reside in the WTP, and there are three MAC architectures, namely, local MAC, split MAC, and remote MAC.
The local MAC architecture means that both the link layer and physical layer functions reside in the WTP. Conversely, the split MAC architecture requires that only the real-time MAC functions reside in the WTP, whereas the AC takes on an role to process the non-real time MAC functions. The real-time MAC functions include beacon generation, probe transmission and response, control frame processing (for example Request to Send (RTS) and Clear to Send (CTS), and retransmission; the non-real time functions include authentication and deauthentication, association and reassociation, bridging between Ethernet and wireless LAN, and fragmentation. In the remote MAC architecture, however, 802.11 MAC functions reside in the AC, which are completely separated from the physical layer functions.
In the local MAC architecture, the WTP processes wireless frames and then encapsulates them into IEEE 802.3 frames before forwarding them to the AC; in the split MAC architecture, the WTP directly encapsulates wireless frames before forwarding them to the AC.
AP management
As a basic function of the AC, AP management includes version management,
configuration management, access control, and domain and group management of APs.
RF management
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Issue 01 (2010-06-25) When radio signals are propagated, they are greatly affected by surroundings.
Specifically, due to multipath options, radio signals encounter complex attenuation in different directions. Therefore, thorough network planning is performed before build-out of a WLAN network. After a WLAN network is deployed, radio signal propagation may also be affected by much interference arising from constant change of the wireless environment, moving obstacles, and operating microwave. Therefore, it is inevitable to adjust parameters. In this case, RF resources such as channel and transmit power must be dynamically adjusted to adapt to changes of application environments.
RF management is to apply a set of systematic real-time intelligent RF methods
(including data collection, data analysis, decision making, and decision execution) to the wireless network, so as to quickly adapt to changes of the wireless environment and maintain the optimal status of RF resources.Figure 8-2 shows the RF management process.
Figure 8-2 RF management process Data collection: APs collect RF environment information in real time according to policies provided by the AC.
Data analysis: The AC analyzes and assesses data collected by the APs.
Decision making: According to the analysis result, the AC assigns channels and transmit power.
Decision execution: APs execute configurations set by the AC and adjust RF resources.
Service set management (ESS profile)
Service set management is to manage certain attributes of a service set, including creating, deleting, modifying, and querying the service set.
Configuration auto-provisioning management
Configuration auto-provisioning management is to manage the creation, modification, deletion, and query of the configuration auto-provisioning rules. Configuration auto-provisioning rules are pre-defined. In this manner, APs can obtain necessary configurations and perform configurations automatically.
Centralized BSSID management
Basic service set (BSS) is a basic component over the 802.11 network, and comprises a group of stations (STAs) that can communicate with each other. Every BSS is assigned a BSSID to uniquely identify the BSS (the BSSID is a binary 48-bit identifier used by all STAs in a BSS).
Centralized BSSID management is a process in which the AC automatically assigns a unique BSSID over the entire network to every VAP, eliminating any need of manual operations.
Load balancing
Load balancing is a method to load the excess STAs on an AP to other APs within the same group as the AP when the quantity of STAs on the AP exceeds the preset user quantity and user traffic threshold.
WLAN STA roaming
When a STA moves at a small area within a deployed WLAN network, the STA may roam from one AP to another. For this scenario, the WLAN STA roaming function is provided.
WLAN STA roaming is a process in which an STA moves from one AP to another.
Currently, Huawei's products support quick WLAN STA roaming within a same AP. That is, if an STA uses 802.1x authentication, 802.1x authentication and key exchange are not performed after the client moves from one AP to another, thus speeding up roaming.
In short, when an STA roams from one AP to another (the two APs are within the same AC), the STA does not need to log in or be authenticated again.
Figure 8-3 shows quick WLAN STA roaming.
Figure 8-3 Quick WLAN STA roaming