Wireless LAN Components and Terminology
Components of a traditional WLAN network include APs, network interface cards (NICs) or client adapters, bridges, repeaters, and antennae. Additionally, an authentication, authorization, and accounting (AAA) server (specifically a Remote Address Dial-In User Service [RADIUS] server), network management server (NMS), and "wireless-aware" switches and routers are considered as part of an enterprise WLAN network.
Figure 1-1 illustrates WLAN components in an enterprise network architecture. Note that only components related to building a Cisco WLAN network are defined in the figure.
Figure 1-1. Components of WLAN System
The following list describes in further detail the WLAN components depicted in Figure 1-1:
Access point (AP)? An AP operates within a specific frequency spectrum and uses an 802.11 standard modulation technique. It also informs the wireless clients of its availability and authenticates and associates wireless clients to the wireless network. An AP also coordinates the wireless clients' use of wired resources. It should be noted that there are several kinds of APs, including single radio and multiple radios, based on different 802.11 technologies.
NIC or client adapter? A PC or workstation uses a wireless NIC or client adapter to connect to the wireless network. The NIC scans the available frequency spectrum for connectivity and associates it to an AP or another wireless client. The NIC is coupled to the PC or workstation operating system (OS) using a software driver. Various client adapters are available from Cisco and CCX vendors.
Bridge? Wireless bridges are used to connect multiple LANs (both wired and wireless) at the Media Access Control (MAC) layer level. Used in building-to-building wireless connections, wireless bridges can cover longer distances than APs. (The Institute of Electrical and Electronics Engineers [IEEE] 802.11 standard specifies one mile as the maximum coverage range for an AP.) Bridges are available for deployment using different 802.11 technologies.
Note
Currently, bridges are not defined in the 802.11 standards; hence, the bridges do not operate on open standards. This means the bridges must be from the same vendor as the WLAN infrastructure.
Workgroup bridge (WGB)? A workgroup bridge is a smaller-scale bridge that can be used to support a limited number of wired clients.
Antenna? An antenna radiates the modulated signal through the air so that wireless clients can receive it. Characteristics of an antenna are defined by propagation pattern (directional versus omnidirectional), gain, transmit power, and so on. Antennas are needed on the APs, bridges, and clients. The antennas need not be conspicuous at all; for example, many PC manufacturers build the antenna inside the LCD screen.
AAA server? AAA services are needed to secure a WLAN network. The AAA server is used for both user and administrator authentication in a WLAN network. It is used for enterprise networks, not home WLANs. The AAA server can be used to pass policy such as virtual LAN (VLAN) and SSID for clients, to grant different levels of authorization rights to administrative users, and to generate dynamic encryption keys for WLAN users. Furthermore, accounting features of a AAA server can be used to track WLAN user activities.
Network management server (NMS)? The NMS is needed to ease the complexity of deployment and management of large WLAN networks. The NMS should support firmware/software management, configuration management, performance trending and reporting, and client association reporting capabilities in a WLAN network. Furthermore, additional capabilities to manage the RF spectrum and detect rogue APs are needed in an enterprise WLAN network. The NMS should be supported by other normal management systems for syslogs, traps, and so on.
"Wireless-aware" switches and routers? To scale and manage WLAN networks, integration between traditional WLAN elements (such as APs, bridges, WGBs, and WLAN clients) and wired network elements (such as switches, access/distribution switches, and routers) is provided by Cisco. Roaming, network management, security, and additional services can be enabled on the wired infrastructure to manage, scale, and provide end-to-end security.
Components discussed in the preceding list integrate with each other to create an end-to-end network to enable mobility in enterprise and vertical markets.
Note
One source of confusion in the WLAN world is that because the WLAN domain leverages many different standards, the same entity is known by many names in different standards and specifications.
The client adapter is also called "STA" (station) or "supplicant" or "peer" in many of the standards. The access point is also known as an "authenticator" or "network access server," because it acts as the point where the client interfaces with the network. The AAA server is also known as an "authentication server," "RADUIS server," or even "access control server (ACS)."
