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This chapter describes the Cisco Aironet Wireless LAN Adapters, also referred to as client adapters, and illustrates their role in a wireless network.
The following topics are covered in this section:
The Cisco Aironet Wireless LAN Adapters, also referred to as client adapters, are radio modules that provide transparent wireless data communications between fixed, portable, or mobile devices and other wireless devices or a wired network infrastructure. 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 transparently through the wireless infrastructure. The adapters operate similarly to a standard network product except that the cable is replaced with a radio connection. No special wireless networking functions are required, and all existing applications that operate over a network will operate using the adapters.
This document covers three types of client adapters:
Refer to the "Radio Antenna" section for antenna differences between these adapters.
Throughout this document, the following terms are used:
The client adapter is composed of three major parts: a radio, a radio antenna, and two LEDs.
The client adapter contains a direct-sequence spread spectrum (DSSS) radio that operates in the 2.4-GHz license-free Industrial Scientific Medical (ISM) band. The radio transmits data over a half-duplex radio channel operating at up to 11 Mbps.
DSSS technology causes radio signals to be transmitted over a wide frequency range, using multiple frequencies simultaneously. The benefit of this technology is its ability to protect the data transmission from interference. For example, if a particular frequency encounters noise or interference or both, enough redundancy is built into the signal on other frequencies that the client adapter usually will still be successful in its transmission.
The type of antenna used depends on your client adapter:
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Note Refer to the Cisco Aironet Wireless LAN Adapters Software Configuration Guide for information on setting the client adapter's antenna mode. |
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Note External antennas used in combination with a power setting resulting in a radiated power level above 100 mW equivalent isotropic radiated power (EIRP) are not allowed for use within the European community and other countries that have adopted the European R&TTE directive or the CEPT recommendation Rec 70.03 or both. For more details on legal combinations of power levels and antennas in those countries, contact Cisco Corporate Compliance. See also the "Declaration of Conformity with Regard to the R&TTE Directive 1999/5/EC" section. |
The client adapter has two LEDs that glow or blink to indicate the status of the adapter or to convey error messages. Refer to Chapter 4 for an interpretation of the LED codes.
The client adapter supports two principal security features to protect your data as it is transmitted through your wireless network: Wired Equivalent Privacy (WEP) keys and Extensible Authentication Protocol (EAP) or LEAP (also referred to as EAP - Cisco Wireless).
WEP is an optional IEEE 802.11 feature that provides your client adapter and other devices on your wireless network with data confidentiality equivalent to that of a wired LAN. It involves packet-by-packet data encryption by the transmitting device and decryption by the receiving device.
Each device within your wireless network is assigned up to four encryption keys, called WEP keys, that encrypt data before it is transmitted. If a device receives a packet that is not encrypted with the appropriate key (as the WEP keys of all devices must match), the device discards the packet and never delivers it to the intended receiver.
For the client adapter, WEP is implemented through the client utilities. In Windows and Linux operating systems, the Client Encryption Manager (CEM) utility allows you to set WEP keys, and the Aironet Client Utility (ACU) is used to enable WEP. In the MacOS 9.x operating system, WEP keys are set and enabled in one utility.
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Note Refer to the Cisco Aironet Wireless LAN Adapters Software Configuration Guide for instructions on setting WEP keys and enabling WEP for your specific operating system. |
EAP is an optional IEEE 802.1x security feature that is ideal for organizations with a large user base and access to an EAP-enabled Remote Authentication Dial-In User Service (RADIUS) server, such as Cisco Secure ACS 2.6. The RADIUS server uses EAP to provide server-based authentication for clients.
Server-based authentication can be enabled for your client adapter in one of two ways:
For Windows 95, 98, NT, 2000, or Me or future Windows operating systems, the Aironet Client Utility setup program, which installs the client utilities, is used to enable LEAP or EAP. After LEAP or EAP is enabled and the computer is rebooted, the client adapter authenticates to the RADIUS server using the username and password entered by the user at the network logon. See the "Installing the Client Utilities and Enabling LEAP or EAP" section for instructions on using the Aironet Client Utility setup program to enable LEAP or EAP.
For Windows CE, Linux, and MacOS 9.x, LEAP is enabled through a particular screen in the client utilities. The username and password entered in this screen are used by the client adapter to authenticate to the RADIUS server. In Windows CE, you do not need to re-enter your username and password after your device is rebooted or your client adapter is ejected. In Linux and MacOS 9.x, the username and password need to be re-entered at the start of each new session. See the Cisco Aironet Wireless LAN Adapters Software Configuration Guide for instructions on enabling LEAP through the client utilities.
When you enable EAP on your Access Points and LEAP or EAP on your client adapter, authentication to the network occurs in the following sequence:
1. The client adapter uses the username and password to start the authentication process.
2. The Access Point communicates with the EAP-compliant RADIUS server to authenticate the username and password.
3. If the username and password are valid, the RADIUS server and the client adapter negotiate a dynamic, session-based WEP key. The key, which is unique for the authenticated client, provides the client with secure network access.
4. The client and Access Point use the WEP key for all data transmissions during the session.
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Note Refer to the IEEE 802.11 Standard for more information on EAP and to the following URL for additional information on RADIUS servers: http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/secur_c/scprt2/scrad.htm. |
The client adapter 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 following common network configurations:
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Note For examples of more complex network configurations involving client adapters and Access Points, refer to the Cisco Aironet Access Point Hardware Installation Guide. |
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Note Refer to the Cisco Aironet Wireless LAN Adapters Software Configuration Guide for information on setting the client adapter's network mode. |
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.
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 allows 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, once 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.
Determining the network location of your wireless products can be influenced by a number of factors. This section discusses those factors and provides guidelines and tools for achieving optimum placement.
The site survey and link test tools provided with the client utilities can help you to determine the best placement for Access Points and workstations within your wireless network. Refer to the Cisco Aironet Wireless LAN Adapters Software Configuration Guide for information on using these tools and to the Cisco Aironet Access Point Hardware Installation Guide for additional information on the placement of Access Points.
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Note The site survey and link test tools are not supported in the Linux operating system. |
Because of differences in component configuration, placement, and physical environment, every network application is a unique installation. Before installing the system, you should perform a site survey to determine the optimum utilization of networking components and to maximize range, coverage, and network performance.
Consider the following operating and environmental conditions when performing a site survey:
The link test tool is used to determine RF coverage. The test results can help the installer to eliminate areas of low RF signal levels that can result in a loss of connection between the client adapter and the Access Point.
Posted: Fri Dec 29 09:00:21 PST 2000
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