Ad-Hoc vs. Infrastructure
Wireless networks typically work in one of two configurations (sometimes called topologies): ad-hoc or infrastructure. The topology or mode you choose depends on whether you want your PCs to communicate directly or with an access point.
In ad-hoc mode (Figure 3.3) data in the network is transferred to and from wireless network adapters connected to PCs. An ad-hoc network is also called a peer-to-peer network. Here are some of the benefits of an ad-hoc network:
Ad-hoc networks are simple to set up. Plug in your wireless network adapters, configure the software, and you're off and running.
Ad-hoc networks are inexpensive. You save the cost of purchasing an access point.
Ad-hoc networks are fast. Throughput rates between two wireless network adapters are twice as fast as when you use an access point.
Figure 3.3. An ad-hoc network with two computers communicating directly.
Now that we've considered the benefits of ad-hoc networks, let's consider the road most people will follow when creating a wireless network. You can increase the range of your wireless network by adding an access point. Wireless networks that use an access point are in infrastructure mode (Figure 3.4).
Figure 3.4. More common than an ad-hoc network, an infrastructure network includes an access point.
An infrastructure network enables you to:
Connect to a wired network. An access point (Figure 3.5) lets you easily expand a wired network with wireless capability. Your wired and wirelessly networked computers can communicate with each other. This is the most obvious strength of an infrastructure setup.
Figure 3.5. This access point from D-Link can be used to connect a cable or DSL modem to provide Internet access to the wirelessly connected computers on your network.
Extend your wireless network's range. Placing an access point in between two wireless network adapters doubles their range.
Utilize roaming ability. If you add multiple access points to your network, as you might in an office or large home, users can roam between interlocking access point cells, without ever losing a connection to the network.
Share the Internet. Probably the most useful device in a simple wireless LAN is an access point with a built-in router and firewall. The router allows you to share Internet access between all your computers, and the firewall hides your network, helping to keep network-savvy hoodlums at bay. Some of these multifunction access points include a (wired) hub as well, for plugging in several computers connected to your network by Ethernet. You can purchase a device like this for less than $200, a real steal for all the use you get out of it.
What about drawbacks? An infrastructure network takes a bit more work than setting up an ad-hoc network. Infrastructure networks cut the data transfer rate about in half, because of the time it takes to send the signal to and from the access point rather than directly to its destination, as in an ad-hoc network. The other drawback is expense: Infrastructure networks are more expensive than ad-hoc networks because you have to purchase an access point. As we already mentioned, however, that expense is well worth it for all the benefits an access point provides.