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Application Note 184 2 ni.com

Applications

Applications for wireless instrument control include the following:

• Controlling portable racks of instrumentation from a wireless-enabled computer

• Controlling instrumentation in a hazardous environment

• Controlling instrumentation where no Ethernet or physical connection is available

• Sharing access to GPIB instruments and systems on a wireless network so several users can download test data or

conduct tests from several wireless-enabled computer stations

Commercially Available 802.11 Routers

This application note details a wireless instrument control system that highlights the Linksys EtherFast Wireless AP

and Cable/DSL Router with 4-Port Switch (Model BEFW11S4). However, you can use any wireless router that follows

the IEEE 802.11 communications standard and that can act as a Dynamic Host Configuration Protocol (DHCP) server.

Other U.S. products that meet these criteria are the D-Link Wireless Router and Access Point + 3-Port Switch (Model

DI-713), the U.S. Robotics Wireless Access Point (Model USR2450), and Apple Computer AirPort Base Station,

among others.

In Europe, similar options exist for wireless networking, including options from 3Com (www.3com.com) and Netgear

(www.netgear.com), however, because of the encryption algorithms, many of the products require export licenses from

the U.S. Department of Commerce.

In Japan, NTT-ME (www.ntt-me.co.jp) sells an 802.11 compliant router – the MN128-SOHO Slotin Air Pack – that

includes a PCMCIA wireless access card.

Performance

Most commercial wireless routers offer throughput up to 11 Mb/s, depending on the encryption level. The Linksys

Etherfast AP provides 40-bit or 128-bit encryption to ensure data security; however, implementing encryption can

significantly slow the data throughput for your wireless system.

With the NI GPIB-ENET/100, you can sustain transfer rates greater than 900 kbytes/s. Used with a wireless router, you

can maintain the same transfer rates for your wireless test system, depending on the level of encryption you choose.

The range of wireless routers varies greatly; however, the Linksys Etherfast AP advertises a range of 91 m indoors and

457 m outdoors. Factors affecting this range are RF noise in your environment and the existence of other wireless

networks in the environment. Most wireless network cards provide utilities for gauging the signal strength of your

wireless connection.

Configuring the Wireless Router

Installation and setup of most wireless routers is surprisingly easy. For the Linksys Etherfast AP, installation of the

wireless router requires connecting the router to a computer or existing Ethernet LAN. Then, using a specified IP

address, you configure the settings for the router – network type (ad hoc or infrastructure), encryption mode, password,

number of users allowed, etc. The computer interface is a Linksys Wireless Network PCMCIA card, which fits directly

into a laptop but must be used with an adapter board for installation in a PCI slot in a desktop PC. With the Linksys

Wireless Network PCMCIA card, configuration consisted of merely selecting the password and encryption type.

Depending on your network and computer configuration, you may need a network administrator to assist in

configuring the wireless network.

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US Robotics USR2450 Manual de usuario Pagina 2