This chapter describes the Cisco Aironet CB21AG and PI21AG client adapters and illustrates their role in a wireless network.
The following topics are covered in this chapter:
•Introduction to the Client Adapters
•Network Configurations Using Client Adapters
Introduction to the Client Adapters
The Cisco Aironet IEEE 802.11a/b/g Wireless LAN Client Adapters (CB21AG and PI21AG) are radio modules that provide wireless data communications among fixed, portable, and mobile devices within both wireless and wired network infrastructures. The client adapters are fully compatible when used in devices supporting "plug-and-play" (PnP) technology.
The primary function of the client adapters is to transfer data packets through the wireless infrastructure by communicating with other clients or with access points that are connected to a wired LAN. The adapters operate similarly to a standard network product except that radios rather than Ethernet cables make the connection to the wire. No special wireless networking functions are required, and all existing applications that operate over a network can operate using the adapters.
This document covers the two client adapters described in Table 1-1.
Table 1-1 Client Adapter Types
An IEEE 802.11a/b/g-compliant 2.4- and 5-GHz 54-Mbps client adapter card radio module with a Cardbus interface that can be inserted into any device equipped with a 32-bit Cardbus slot. Host devices can include laptops and notebook computers.
An IEEE 802.11a/b/g-compliant 2.4- and 5-GHz 54-Mbps client adapter card radio module that can be inserted into any device equipped with an empty PCI expansion slot, such as a desktop personal computer.
The following terms are used throughout this document:
•client adapter—Refers to both types of adapters.
•PC-Cardbus card or PCI card—Refers to a specific adapter.
•workstation (or station)—Refers to a computing device with an installed client adapter.
•infrastructure device—Refers to a device that connects client adapters to a wired LAN, such as an access point, bridge, or base station. Throughout this document, access point is used to represent infrastructure devices in general.
The client adapters have three major hardware components: a radio, a radio antenna, and two LEDs.
The client adapters contain a dual-band radio that is both IEEE 802.11a and 802.11b/g compliant. The radio uses both direct-sequence spread spectrum (DSSS) technology and orthogonal frequency division multiplexing (OFDM) technology for client applications in the 2.4-GHz Industrial Scientific Medical (ISM) frequency band and OFDM technology in the 5-GHz Unlicensed National Information Infrastructure (UNII) frequency bands. The client adapters operate with other IEEE 802.11a or 802.11b/g-compliant client devices in ad hoc mode or with Cisco Aironet access points and other IEEE 802.11a or 802.11b/g-compliant infrastructure devices in infrastructure mode.
The type of antenna used depends on your client adapter:
•PC-Cardbus cards have an integrated, permanently attached 0-dBi gain, dual-band 2.4/5-GHz diversity antenna. The benefit of the diversity antenna system is improved coverage. The system works by enabling the card to sample and switch between its two antenna ports in order to select the optimum port for receiving data packets. As a result, the card has a better chance of maintaining the radio frequency (RF) connection in areas of interference. The antenna is housed within the section of the card that hangs out of the Cardbus slot when the card is installed.
•PCI cards have a 1-dBi gain, dual-band 2.4/5-GHz antenna that is permanently attached by a 6.6-foot (2-meter) cable. A base is provided with the antenna to enable it to be mounted to a wall or to sit upright on a desk or other horizontal surface.
The client adapters have two LEDs that glow or blink to indicate the status of the adapter or to convey error messages. Refer to Chapter 10, for an interpretation of the LED codes.
The client adapters have two major software components: a driver and client utilities. These components are installed together by running a single executable Install Wizard file that is available from Cisco.com. This file can be run on Windows 2000 or XP and can be used only with CB21AG and PI21AG client adapters.
Note Chapter 3, provides instructions on using the Install Wizard to install these software components.
The driver provides an interface between a computer's operating system and the client adapter, thereby enabling the operating system and the applications it runs to communicate with the adapter. The driver must be installed before the adapter can be used.
Two client utilities are available for use with the client adapters: Aironet Desktop Utility (ADU) and Aironet System Tray Utility (ASTU). These utilities are optional applications that interact with the client adapter's radio to adjust settings and display information.
ADU enables you to create configuration profiles for your client adapter and perform user-level diagnostics. Because ADU performs a variety of functions, it is documented by function throughout this manual.
ASTU, which is accessible from an icon in the Windows system tray, provides a small subset of the features available through ADU. Specifically, it enables you to view status information about your client adapter and perform basic tasks. Chapter 8, provides detailed information and instructions on using ASTU.
Note If your computer is running Windows XP, you can configure your client adapter through the Microsoft Wireless Configuration Manager (or another third-party tool) instead of through ADU. Refer to Appendix E, for information. However, ADU is recommended for configuring the client adapter.
Network Configurations Using Client Adapters
Client adapters can be used in a variety of network configurations. In some configurations, access points provide connections to your network or act as repeaters to increase wireless communication range. The maximum communication range is based on how you configure your wireless network.
This section describes and illustrates the two most common network configurations:
•Ad hoc wireless local area network (LAN)
•Wireless infrastructure with workstations accessing a wired LAN
For examples of more complex network configurations involving client adapters and access points, refer to the documentation for your access point.
Note Refer to Chapter 5, for information on setting the client adapter's network type.
Ad Hoc Wireless LAN
An ad hoc (or peer-to-peer) wireless LAN (see Figure 1-1) is the simplest wireless LAN configuration. In a wireless LAN using an ad hoc network configuration, all devices equipped with a client adapter can be linked together and communicate directly with each other. The use of an infrastructure device, such as an access point, is not required.
Figure 1-1 Ad Hoc Wireless LAN
Wireless Infrastructure with Workstations Accessing a Wired LAN
A microcellular network can be created by placing two or more access points on a LAN. Figure 1-2 shows a microcellular network with workstations accessing a wired LAN through several access points.
This configuration is useful with portable or mobile stations because it enables them to be directly connected to the wired network even while moving from one microcell domain to another. This process is transparent, and the connection to the file server or host is maintained without disruption. The mobile station stays connected to an access point as long as it can. However, when the transfer of data packets needs to be retried or beacons are missed, the station automatically searches for and associates to another access point. This process is referred to as seamless roaming.
Figure 1-2 Wireless Infrastructure with Workstations Accessing a Wired LAN