Installing a Wireless LAN
After all of this explanation, you might be surprised to discover that setting up a wireless LAN is not all that difficult. For the home or small business user, it can be extremely simple, because many of the wireless products are designed to use default configurations that are suitable to that environment. In an enterprise environment, the situation is more complicated, and administrators might have to spend more time examining the site and evaluating products before they buy.
Examining the Site
In most cases, people consider installing a wireless network because a wired one is not practical for some reason. The installation of the cables might be too difficult or too expensive, or there is something preventing them from using a traditional Ethernet LAN. However, before you settle on 802.11 wireless as your solution, you should consider the possible complications of that as well.
A site survey is the first step in a wireless LAN deployment. Even though you might have already examined the location before rejecting a wired network as a possible solution, you should take another look when considering wireless—the criteria governing a wireless installation can be different. Distances are still a concern, because wireless devices have limited range, but the measurements you take will have different implications. For a wired network, you try to estimate the length of cable routes inside walls and ceilings, whereas wireless distances are direct routes through walls and other obstructions. You must have some idea of the maximum distances your devices will have to transmit. If those distances are well beyond the estimated ranges of the equipment you are considering, then you might have to add some form of range enhancement, such as a larger antenna. You might also consider building an ESS with multiple access points or installing multiple separate LANs.
Wireless transmission distances are also subject to interference from obstructions. The more walls there are between two wireless stations, the shorter the distance across which those stations can transmit successfully. You must also consider the composition of the walls. A typical office with drywall dividers will generate much less interference than a school building with cinderblock walls.
You must consider other potential sources of interference as well. Refrigerators, microwave ovens, and other electrical equipment can all interfere with wireless signals, some of them in maddeningly intermittent ways. A microwave oven, for example, might block all wireless traffic in the vicinity, but only when it’s running. This is the sort of situation that drives technical support people insane.
Another factor to consider is interference from other wireless networks in the area. Most wireless devices are capable of scanning for other networks and displaying information about them, including their SSIDs, the channels they use, and their strengths. This will tell you what channels to avoid, and help you to make sure you don’t duplicate a local SSID. You might also discover that the band you are scanning is so crowded that you should consider another one. Most of the 802.11 equipment on the market uses the 2.4-GHz band, and if you detect dozens of other networks in the area, the additional expense for equipment using the 5-GHz band might be worthwhile.
Using the information from your site survey, you should be able to determine approximate locations for your access points. Obviously, your first priority is to provide network access to all of your clients, but there are also security considerations involved in access point placement. Placing an access point too near an outside wall could enable outside users to gain access to your network.
Most access points come equipped with dipole antennas, which are omnidirectional. Therefore, placing access points near the center of the space you want to service is the usual procedure. However, some access points permit you to connect an external antenna, as shown in Figure 5-9, and there are a variety of other antenna designs that can provide greater or more directional coverage.
Figure 5-9. An external wireless LAN antenna.
One of the nice things about constructing a wireless LAN when compared to a wired network is that there are far fewer bits and pieces to buy. Every computer you want to connect will need a wireless network interface adapter and, if you are building an infrastructure network, you will need at least one access point. Barring exceptional circumstances, that’s it. You don’t need cable components or wall plates or patch panels, and there are no special tools required for the installation.
Selecting Network Interface Adapters
Nearly all desktop computers have integrated Ethernet ports on their motherboards, but very few come with wireless LAN adapters. Virtually all of the mobile computing devices sold today, including laptops, netbooks, and tablets, come equipped with 802.11 network interface adapters, but the actual configuration of those adapters can vary widely.
Some new devices have 802.11b/g adapters, and others have 802.11b/g/n. Older devices might have only 802.11b. In addition, administrators often find that they can retrofit some of the mobile devices with different adapters, but others are not upgradable.
When you are equipping new computers with adapters, it is easy to standardize on one configuration or one device, but enterprise administrators often have to accommodate a variety of devices of varying ages. This is why access points often need to be as compatible as possible with every standard on the market.
With a highly compatible access point, administrators are free to purchase wireless network adapters to suit the needs of their various users. An adapter for a desktop computer usually takes the form of a standard expansion card with an antenna protruding through the slot cover, as shown in Figure 5-10. Adapters for mobile computers can take various forms, some with external antennae and some with internal.
Figure 5-10. An internal 802.11 wireless network interface adapter.
Selecting Access Points
Wireless access points are available as stand-alone devices—most commonly used in enterprise settings—or integrated into multifunction devices, which are more popular for home and small business networks.
A stand-alone access point is a simple-looking device with a single port for a wired network connection, usually an RJ45, and one or more antennas, as shown in Figure 5-11. The physical installation of an AP is as simple as plugging it into a power source and connecting it to your Ethernet network. Then, any wireless device that connects to the AP can access the wired network, and wired devices can access the wireless ones.
Figure 5-11. A stand-alone 802.11 wireless access point.
Multifunction devices that contain wireless access ports are usually designed as broadband routers that connect home or small office networks to the Internet. A typical multifunction device configuration will have an RJ45 port for a WAN connection—usually to a cable or DSL modem—and a number of switched RJ45 ports for Ethernet connections, as shown in Figure 5-12. The device might also contain additional internal functions, such as a firewall, a Dynamic Host Configuration Protocol (DHCP) server, and a Network Address Translation (NAT) router.
Figure 5-12. A multifunction device containing an 802.11 wireless access point.
The biggest concern when selecting hardware for a wireless LAN is compatibility. You must make sure that your devices can connect to each other, and do so with the appropriate levels of performance and security you need.
The following sections examine the compatibility factors you might have to consider when evaluating 802.11 wireless equipment.
The vast majority of 802.11 wireless products on the market support a variety of standards. IEEE 802.11b/g devices are probably the most prevalent, and there are now many 802.11b/g/n devices as well. Some higher-end devices add support for 802.11a also, which means they can use the 5-GHz frequency band, probably with the 802.11n standard also.
It is also common practice for manufacturers to begin releasing equipment supporting the latest standard before the standard has actually been ratified by the IEEE. There will, no doubt, be 802.11ac devices arriving before long, but it is always a gamble to purchase equipment before the standard is finalized and ratified.
One of the trickiest aspects of the wireless standard development process has always been backward compatibility with the previous standards. There is little doubt that if you purchase a device based on a draft standard, it will work with other devices also based on that standard, but whether it will work with your older equipment is another question that you should explore carefully before you invest in a new technology.
If you are building a brand-new network, buying all new computers and access points, interoperability is easy to achieve. Problems arise, though, when you have existing computers that must work with your new equipment. When it comes to purchasing multistandard products for an infrastructure network, remember that the computers must be compatible with your access point, but they don’t have to be compatible with each other.
Therefore, the safest course of action is to purchase access points that support all of the standards you are likely to find in your computers, as shown in Figure 5-13. 802.11a/b/g/n access points are readily available, and the technology has matured to the point that they are affordable for most administrators’ budgets.
Figure 5-13. A multistandard access point connected to devices using various standards.
A wireless LAN is a massive security hole for several reasons, and protecting your network by encrypting your transmissions is no longer optional; you must do it. To ensure complete protection and complete connectivity, all of the devices on your network must support the exact permutation of the security protocols you plan to use. After you configure the security on your access point, any devices that do not support those protocols will not be able to connect.
Network interface adapters can connect to computers in many ways, and before you purchase wireless equipment, you must consider your alternatives. USB adapters are easy to install, and most computers have an extra USB port available, but the USB interface might prevent your systems from realizing their maximum performance levels.
Internal adapters are preferable, but before you purchase them, you must determine three things:
What type of slots are in your computers
Whether a slot is free
Whether a slot is accessible
Most 802.11 wireless LAN equipment uses the 2.4-GHz frequency band, but as discussed earlier, there are reasons why you might not want to or be able to use that band for your network. If you want to take advantage of the 40-MHz channel width in 802.11n, or if the 2.4-GHz band is simply too crowded in your area, then you might want to use the 5-GHz band supported by 802.11a and 802.11n.
Be aware, however, that a device that complies with the 802.11n standard does not have to support the 5-GHz band. You must look for devices marketed as dual band or that explicitly say they support the 5-GHz band in 802.11n.
IEEE 802.11n devices are a popular choice among users and administrators, due to their potential for high performance. However, the 802.11n standard presents compatibility issues other than the frequency band. As discussed earlier in this chapter, an 802.11n device can have from one to four MIMO spatial streams and can conceivably support 20-MHz and 40-MHz channel widths.
Here again, you must consider that the compatibility you need is between your access points and your computers, not between individual computers. Therefore, the access points you select should have the highest level of performance that you want to achieve. Then you can purchase 802.11n network interface adapters at various price points, depending on the performance level you need for each computer.
Installing and Configuring Wireless Hardware
Wireless access points have built-in web servers that provide their configuration interfaces, so after connecting the device to the network, you only have to use a browser to connect to its IP address and authenticate by using a default password supplied with the product documentation. After that, the first order of business is to change the password and configure the device with an appropriate IP address and TCP/IP configuration settings for your network.
The first step in configuring the wireless attributes of an access point is to specify an SSID other than the default and select the band and channel you want the device to use. Most products use standard web-based controls for this purpose, as shown in Figure 5-14. On other pages, you can select the security protocols the device will use and specify any additional information, such as pre-shared keys and other parameters.
Figure 5-14. A web-based interface for a wireless access point.
If you are using multiple access points for your network, you must configure them with the same SSID, but use different channels so that they do not interfere with each other. This is the type of situation in which administrators often apply a multiple-channel architecture, using nonconflicting channels for adjacent access points, as shown in Figure 5-15. This enables the network to cover a large area without having the access points interfere with each other. Clients can wander into the area of a different access point, and the wireless adapter will compensate by changing to the appropriate channel.
Figure 5-15. A multiple-channel architecture.
When the access point is operational, the next step is to configure the network adapters in the computers and other devices to use the same settings. In some cases, the operating system provides a configuration interface for the wireless device settings, whereas in others you must use a configuration utility supplied by the manufacturer of the adapter. In either case, the settings you specify for the adapter must match those of the access point, or the two will not be able to communicate.