Wireless net proves field ready
- By Michelle Speir
- Oct 04, 1998
Testing By Chip Pettirossi
Just as cellular telephones introduced a new kind of personal mobility, wireless networks make yet another aspect of modern life portable. No longer must computer users be tied to stationary machines to access a network— networking is now possible even without hard wiring.
But for now, wireless networking is still a small and specialized market. The performance of wireless local-area networks cannot compete with that of wired networks. Plus, the technology is more expensive, so it is more appropriate for situations where wiring is inconvenient or impossible. The largest markets for wireless LANs are schools and other locations where buildings may be historic or simply too old to accommodate modern wiring.
The federal government is using wireless networking in other capacities as well. The U.S. Border Patrol uses wireless technology at its San Clemente Checkpoint on Interstate Highway 5, just north of San Diego, where a bar code system allows pre-approved commuter cars to pass through the checkpoint without stopping.
The border project began when Congress mandated that an exclusive commuter lane be built at the checkpoint to ease backups caused by four lanes of heavy traffic. "We had to use wireless technology since there are no LAN drops out on the freeway," said Luis Amavizca, watch commander at the Border Patrol.
At the checkpoint, a PC inside the station is connected to a database that contains the codes of approved vehicles, which have bar codes on their sides. About 500 feet away, a bar code scanner scans each car passing through. If a nonapproved car drives through, a red light comes on and the patrol stops the car for inspection.
Amavizca and his staff are happy with the frequency-hopping spread-spectrum technology their wireless system uses to transmit data because it does not interfere with the operations of Camp Pendleton, a nearby military base. "I don't have anything bad to say about it," he said.
Amavizca said that about 3,500 cars are participating in the program, which requires an application and a background check. "From July 1997 to June 1998, the cars passed through the checkpoint about 50,000 times," he said.
Another federal agency that found wireless networking useful is the Small Business Administration in Santa Ana, Calif., home of the Disaster Home Loan Portfolio Office. A recent growth spurt required the office to bring in temporary employees, and wireless connections were much easier than buying and installing hubs and wiring, according to Robert Wharton, computer specialist at SBA.
Wharton said the agency installed wireless LAN adapters in several workstations and then used carts to transport them to the temporary workers. "It worked out pretty darn well," he said. One downside was somewhat slow performance, but SBA was using large databases, which can slow down even wired systems. Wharton said he was happy with the setup and performance overall, and he hopes SBA can use wireless networking in the future when it sets up temporary offices at disaster areas.
Our Test Results
To see how well today's wireless LANs operate, we installed Proxim Inc.'s RangeLAN2 in our FCW Test Center. What we found is that although wired networks are faster than wireless networks, the performance of the Proxim wireless network was quite acceptable.
To test the RangeLAN2, we connected an access point to one of our servers using Ethernet, and we used one desktop computer and one notebook computer as the clients. Our setup used frequency-hopping spread-spectrum technology for security and interference-minimizing purposes. The data rate was 1.6 megabits/sec and the throughput was 500 kilobits/sec.
The RangeLAN2 will support 50 to 80 light data users (running a bar code application, for example), 20 to 40 thin-client users and 10 to 15 heavy data users (running applications such as dBase), according to Proxim.
To increase security, each unit on the RangeLAN2 requires a security ID to establish communication. This ID is encrypted and stored in the access point itself, not in any software. You cannot access the security ID, but you can change it. If you do change it, you also must change the security ID of all other units with which the access point is communicating.
To test the Proxim wireless LAN, we first installed our access point. The ports are labeled clearly, and the unit features several useful status-indicator LEDs. The unit supports 10Base-T or 10Base2 Ethernet networking. We were able to quickly assign an Internet Protocol address, subnetwork mask and gateway address to the access point.
To assign the IP address, we used a null modem cable accessed through the Microsoft Corp. Windows HyperTerminal utility. The unit also supports BOOTP for dynamic IP addressing. We noted that an initial, vendor-assigned Telnet password was missing, which is a security concern. World Wide Web browser management was enabled by default, so we assigned a user name and password for it.
One configuration option that administrators have is to prevent data packets that originate on the Ethernet network from traversing the wireless network based on common networking protocol filters. Administrators also can enable Simple Network Management Protocol management of the access point, but they may first need to adjust the radio configuration settings that are discussed in the users manual.
We used the site-survey configuration tool to ensure proper placement of the access point so its performance would be maximized. This tool indicates link quality using a five-point scale, and signal strength is measured in a percentage ranging from 0 to 100.
RangeLAN2 features a basic Web browser management interface that is short on graphics and icons but still easy to use. It includes three handy network management applications. One is a discovery tool, which locates all access points on the network. You can double-click on an access-point icon to view the main management window for that unit. Other tools include a network map that shows all connected wireless devices and a traffic monitor that displays network traffic in a graphical view.
The device management module includes many useful functions. You can collect Ethernet and radio statistics to monitor performance, and a system information window displays current ROM versions and Mandatory Access Control addresses. A helpful status window indicates the number of connected wireless LAN stations, and a software download feature allows you to update system code. One problem was that we could not access the diagnostic screen from our Web browser.
The wireless LAN adapter for a desktop PC is called the RangeLAN2 7100. We were a bit puzzled that the card is a non-plug-and-play ISA card instead of a PCI card, as PCI cards are today's norm. We installed the card into an ISA slot and plugged the antenna into the card without any problems.
The bundled LAN drivers support Novell Inc.'s NetWare and Microsoft Windows 95, Windows NT and Windows for Workgroups. After we installed the card driver, we received conflicting status information: The DOS test utility found the LAN adapter and reported that it was functioning properly, but the site-survey tool recorded an error with the adapter installation. It turned out there was indeed a problem in the form of an interrupt request conflict that we fixed.
Once the LAN card was successfully installed, we were able to easily browse the network and find our resources.
Installing the PC card on our notebook computer proved to be a snap. The card is called the RangeLAN2 7401, and unlike the 7100, it has full plug-and-play capability. Windows automatically detected the card when we inserted it.
We then inserted the driver diskette, and Windows correctly installed the software when we rebooted. Next, we loaded Microsoft networking services and configured the Transmission Control Protocol/Internet Protocol to operate on our network.
The final step in setting up the notebook was installing the antenna. The antenna is about 3 inches long and resembles a small pen. It attaches to the case of the computer with a special adhesive-backed holder. It is connected to a foot-long wire that snaps into the PC Card. We also loaded Proxim's network utilities program onto the notebook. Windows 95 install wizards made the procedure a breeze.
To test the staying power of the RangeLAN2 connections, we subjected our notebook to several operating conditions. We found that the notebook retained its network connection upon waking from sleep mode, but lost it upon waking from suspend-to-disk mode.
We also took the notebook to different locations in our office. The connection was affected by factors such as elevator shafts and concrete walls. One test location, which was on the other side of the elevators from the access point, did not sustain the network connection. However, another location that was about the same distance away but obstructed only by plaster interior walls retained the connection.
We even took the notebook into our office kitchen to test the effect of microwaves on the connection. With the microwave oven off, the link quality fluctuated between four and five, but when the microwave was running, the link quality degraded to one and two, thereby losing the network connection. A link quality above three is required to sustain the network connection.
We tested performance by executing file transfers of bitmap, text and spreadsheet files as well as playing stored video (MPEG) files over the network. For the notebook and desktop computers, we compared wireless to wired performance. As expected, wired performance was superior for all types of files on both types of computers. However, the performance of the wireless network was still acceptable except in the case of stored video playback.
Federal pricing for the RangeLAN2 components is as follows: Access point, $1,592; PC card, $527; and ISA card, $528.
Proxim has developed a compact, user-friendly product that does not require a whole lot of special knowledge to operate. Keep in mind that wireless networking is a niche market. Its performance and price will probably never catch up to wired networking, but it offers a great solution when you need a network but can't install wiring or if your users require mobility. Before you buy, evaluate your needs. Consider the number of users you'll have, the type and amount of traffic that will traverse the network and your physical environment.
How Wireless LANs Work
How does a wireless local-area network work? In place of data cabling, a wireless LAN uses radio waves to transmit information from the network server to a workstation. Frequency hopping and other measures protect the network's security. A transmitter/receiver device, called an access point, connects to the server using standard cabling. The access point is a rectangular box about the size of a cigar box that can be mounted on a wall or ceiling or simply placed on a flat surface.
Access points can accommodate multiple clients, but the number of clients depends upon the number and nature of the transmissions. An access point can generally support 15 to 50 users and has a range of 500 feet indoors and 1,000 feet outdoors.
To receive the data, an end user must have a wireless LAN adapter installed in their PC. These adapters are in the form of PC cards for notebook and palmtop computers and cards for desktop computers. Both types of cards feature ports for pen-size antennas to connect to them.
Wireless networks can take several forms. The most basic is a peer-to-peer network, in which two PCs equipped with wireless adapter cards can be set up to communicate with each other. This setup only allows the machines to communicate with each other and not with a central server.
In a typical client/server setup, multiple access points can be used to extend the range of the network. The access points are installed so that coverage areas overlap, allowing an end user to seamlessly move through a cluster of areas. This ability is called roaming.
Devices called extension points can extend the network even further.