Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

Also known as a Network Interface Card (NIC), PC card, or PCMCIA card, these devices contain the radio, which allows mobile computing to access a wireless LAN. For an employee to use a WLAN, he or she must have a computing device that is equipped with wireless 802.11a, b, g, or dual-mode (depending on the specification the WLAN uses) capability. This capability can be provided via a wireless network interface card. Wireless NICs come in a variety of forms-ISA, PCI, USB, PCMCIA Card, and Compact Flash.

Figure 20.1: Wireless network interface cards come in many different forms.

To add wireless networking capabilities to a stationary PC, the PC will need a wireless NIC. These wireless NICs can come in a variety of form factors, e.g. ISA, PCI, USB or PC adapter (if a PCMCIA card, more commonly referred to as a PC card, is to be used with the stationary PC), since such a card allows you to use a PCMCIA card with the average desktop workstation.

To add wireless networking to a mobile computing device such as a tablet PC, laptop, PDA, or handheld computer, you will need a PCMCIA card (or Compactflash card in the case of some PDAs) that can plug into one of the device's free PCMCIA slots (or in the case of some PDAs and handheld computers, a module that can be slipped into or connected to the device). Note that since 2002, many mobile computing devices ship from the factory with embedded Wi-Fi capability.

Selection Criteria

There are many different computing devices and diverse computing environments and all require consideration when equipping a computing device with a wireless network interface. This list should help the deployment team with their selection process.

• If the WLAN is based on 802.11a technology, consider purchasing dual-mode cards for all mobile computing devices, since 802.11b is the technology used in most HotSpot locations and in most home wireless networks.

• When equipping a desktop computer with a wireless NIC, opt for a card with an external antenna. If you use a NIC with an internal antenna, the path from the antenna to the access point must go through the machine, impairing performance. An external antenna will normally provide about 15% more signal strength, if the external antenna is placed in a position so that signals don't encounter obstacles.

• Be sure that the NIC's drivers support the device's operating system. While virtually all cards support Windows OS, and some support Apple, it may be more difficult to find cards that support Linux, Windows CE, Palm, etc.

• Be cognizant of the fact that you can have choices in antennae; for example, sometimes an extension antenna is available as depicted in Fig. 18.15's PCI card with external antenna. When adding wireless capability to a stationary computer, such an antenna is desirable because it allows the signal to avoid some of the clutter that surrounds these types of computing devices.

• Cards from various vendors can provide very different range limits. Access points may provide coverage to one card and deny it to another in the same location. This is the result of the basic radio frequency (RF) performance of the radio's transmitter/receiver. Some vendor radios can boost their power for greater coverage performance.

• Features over and above the IEEE 802.11a/b/g standards, such as EAP security are not interoperable among different vendors; features such as load balancing will not work with a mix of station radios. This means that you must take the effort to differentiate between what a card offers in the way of 802.11 standard features and vendor proprietary features.

• The functionality that all wireless NICs should have in common includes: modulation (translate baseband signal to a suitable analog form); amplification (raise signal strength); synchronization (carrier sense); error checking.

• Because most WLANs are based on the features and functionality of the access points, it's important to ensure that whatever vendor product you settle on, the NIC's radio can be made available in a wide range of clients—laptops, PDAs, handhelds computers (if applicable), inventory tracking terminals, and perhaps even telephones

• What flavor—a, b, g—dual mode? Dual mode, while having some drawbacks, may be the answer if the mobile computing device is to be used in different network settings, i.e. home, HotSpot, and corporate.

• If you are equipping a desktop computer with a wireless NIC, the card should have an external antenna. If you use a NIC with an internal antenna, the path from the antenna to the access point must go through the machine, impairing performance. An external antenna will normally provide about 15% more signal strength if the external antenna is placed in a position so that signals don't encounter obstacles.

• Consider using an external antenna, even with mobile computing devices. Users that use mobile computing devices (e.g. laptops, tablet PCs, and PDAs) with either a NIC with an internal antenna or one with a built-in NIC, may find that moving the device only a short distance can cause a noticeable difference in signal strength.

• When considering NICs with external antennae, note that a quarter-wave external antenna for a PC card is about 1.25 inches long and a full-wave antenna is about 5 inches long.

• Choose NICs that support password-protection of attribute changes, to prevent the settings of the network cards from being illegally or accidentally changed by users.

• Performance among various types and brands of NICs differ because of the individual NIC's drivers and setup routine.

• If you need antenna diversity, look for cards that offer that choice; you may also want to consider cards that have a plug that can be removed, so that you can plug in an external antenna to improve range.

• If buying PCI adapters for stationary PCs, determine in what environment the adapter will and will not work—some PCI adapters will only work in an all-PCI system, so if the computer has ISA and PCI slots, the adapter won't work.

• When purchasing PC card adapters, check the card ejector button on the adapter to determine if it works smoothly; you don't want an adapter that makes it hard to put the card into the PC.

• If you are purchasing wireless NICs for handheld computers and PDAs, be aware that most (but not all, e.g. HP's iPaq is equipped with a PCMCIA slot) require the purchase of not only the NIC but also additional equipment, such as the Xircom Wireless LAN module for Palms, the Springport Wireless Ethernet Module for Handsprings, or a PC Card sleeve.