Building Blocks for a Wireless LAN

So you’ve decided to incorporate wireless equipment in your existing wired LAN? Deciding on the type of equipment is not very difficult as currently there are only a handful available. The cost of this equipment however is quite high. The difficult part, after getting the government licenses and equipment, is the design consideration. You have to first do a site survey and determine where all you want wireless coverage. How well do they penetrate your office building walls is the next question, because this will affect the wireless range. Then comes security, and the number of nodes that will share a single access point. The latter density of wireless nodes is very important because access points communicate with them through broadcast. If you’ll do huge file transfers from one station, then throughput that the other nodes might be affected. Having taken these considerations into account, here are the main devices in a wireless LAN, followed by some vendor solutions.

Wireless cards



This is perhaps the most essential component of a wireless LAN. These perform the same functions as Ethernet cards in a wired network. Almost all the wireless cards now available use PCMCIA to connect, and thus cannot be used on desktop computers. However, PCI adapters are available that accommodate these cards and connect to a free PCI slot in an ordinary desktop PC. 

Access points



Wireless networks can be formed in two basic ways: Ad-hoc and Infrastructure. Under Infrastructure, all wireless cards connect to a central access point that provides them connectivity with each other as well as the wired network (if available). 

In Ad-hoc mode, access points aren’t used, and all wireless cards form a peer-to-peer network. Access points can vary greatly in features depending on their cost–for example, some access points give you an option of roaming where wireless clients can transparently switch from one AP to another. 

Three kinds of Access points are currently available. The first here are those that don’t communicate with other access points and do not perform any bridging functions. Without bridging, your computers on one wireless network will not be able to see computers present on another. The next kind is access points that act as bridges, which are also come with different options. These include: 

• Point to point. These are used to connect two LAN segments together. These either use the Master/Slave configuration, or let you control which bridge unit you connect to using its MAC address.
• Point to multi-point. Here all bridge units communicate with each other wirelessly.
• Repeater. In the first two modes, bridging units talk only to each other, and do not connect to wireless clients.

Thus, such units are mostly used for connecting two wired networks. However, in the ‘repeater’ mode, a bridge unit not only supports AP-to-AP bridging, but also wireless client to AP. These are also usually the most expensive.

Mixed Media Router 



Instead of using bridging units, one also has the option of using MMR (Mixed Media Router) for connecting different networks to each other. This is usually the cheapest solution, since it is mostly implemented in software on a machine that is connected to all the networks. 

Other products



Some other 802.11b based products have also started appearing in the market. These include wireless Internet cameras, presentation gateways, and print servers. With more such devices coming into the market, networks will become even more flexible.

D-Link’s Wireless Kit 

The D-Link wireless equipment that came to us for review included not only PCMCIA cards and an access point, but also included PCMCIA adapters that could fit into a PCI slot of a desktop computer. Setting up the hardware was very easy; we connected the access point to our network and plugged in the cards using the PCMCIA adapters on our desktop machines. Once the access point has been detected, wireless NICs act exactly the same as their wired equivalents. 

Its access point (DWL-1000AP) is a small device about the size of an external modem, with an adjustable antenna for maximum range. A reset button restores the device to factory settings. It comes with a software package called D-Link AP Manager that is used to access the AP remotely and configure it. This package lets you adjust features like WEP (only 64-bit) and

SSID. Some other useful features are the ability to enter a passphrase instead of a hexadecimal key when using

WEP, and locking the AP so that nobody is able to administer it unless the device is reset.

The wireless cards (DWL-650) along with the PCI adapters (DWL-500) can be run in either one of two modes: ad hoc or infrastructure. In ad hoc mode wireless cards are able to communicate with each other without using an access point, and form a kind of P2P network. In infrastructure mode these cards communicate with an access point. A useful configuration utility not only lets you adjust WEP and

SSID, but also shows the signal strength and quality. 

Overall, the kit worked very well in our tests. Range can vary greatly depending on the number and kind of obstructions. According to the specs, this will have a range of 35-100 m indoors and 100-300 m outdoors. As the distance increases, most 802.11b devices (including this one) are able to step-down their speed sequentially to maintain connectivity. In our tests, a 79 MB file was transferred in approximately 156 secs giving a net throughput of 4 Mbps.

Surecom Wireless Kit

Surecom’s set had the EP-9500 access point, EP-9427 PCMCIA LAN card, and a PCI adapter for connecting this PCMCIA card to a desktop computer, and a product that we haven’t seen before: a 802.11b USB dongle (EP-9001). The features of this are similar to D-Link’s. The EP-9427 has the same software. It has similar monitoring options like signal strength and quality, WEP, SSID, channel setting. But the pass-phrase feature was missing. On the positive side, the Surecom access point also supports 128-bit WEP, and seems to have slightly greater range. This can be due to the two adjustable antennas on the EP-9500. We also tested the Surecom and D-Link kits for compatibility and they worked flawlessly. The Surecom kit (access point + PCMCIA card) took about 149 secs to transfer a 79 MB file, thus giving a throughput of 4.2 Mbps. But, the USB dongle was slower at roughly 3.2 Mbps.

Anuj Jain 

Cisco Aironet 340 Series

We had reviewed this wireless set earlier in December last year. This wireless kit has an access point and two PCMCIA wireless network cards for laptops. It uses RF for communication and claims connectivity over 300 feet at a maximum baud rate of 11 Mbps. What’s more, with multiple access points installed, a wireless client can move transparently across locations and still remain connected, much like a cellular network’s roaming facility, but of course within the office premises. 

The kit comes with two quick-start manuals for the access point and PCMCIA cards, and there’s comprehensive documentation on the CD explaining the product, its components, usage and configuration. The CD also has software for doing a site survey and testing the link’s signal strength, quality, and key management software for encryption. Both provide a graphical feedback for quick analysis. 

The access point is small, lightweight and can be kept on a table or mounted on a wall. It has a serial and network port for managing and connecting to the network respectively. It can either be assigned a static IP address or accept an IP from a DHCP server on your network, making it easy to configure. Once you know its IP address, subsequent configurations can be done through telnet or Web browser. It also runs a DHCP server, for assigning IP addresses to wireless clients. It also supports encryption of data traffic for security. Access control to the wireless network is also possible by specifying the MAC address of each wireless PCMCIA card. Apart from that you can monitor network statistics, connected wireless clients, data transfers and other parameters. The access point can also be configured to work with a router, name server, FTP server and time-server on your network. 

Setting it up is a breeze, and we checked its connectivity by taking a wireless notebook around our office building. We continuously pinged the access point and also looked at the connection’s rating using the ‘Link test’ program that comes with the wireless kit. Overall, the connection was steady, with poor connections or disconnects occur- ring only if there were major obstructions in between. 

We also transferred about 616 MB of data across a wireless notebook and a wired desktop machine, and from one wireless notebook to another. The former took 30 mins and 26 secs while the latter took 27 mins and 52 secs. We did this test when the link was rated as ‘excellent’. This time to transfer increased as we moved away from the access point due to reduction in signal strength. While the product’s performance is very good, its price is quite high. 

Shekhar Govindarajan