Not all Wi-Fi networks are created equal. Wi-Fi access points can function in either “ad-hoc” or “infrastructure” mode, and many WI-Fi-enabled devices can only connect to infrastructure-mode networks, not ad-hoc ones.
Wi-Fi networks in infrastructure mode are generally created by Wi-Fi routers, while ad-hoc networks are usually short-lived networks created by a laptop or other device. But it isn’t always so simple.
Infrastructure and Ad-Hoc Modes Explained
Most Wi-Fi networks function in infrastructure mode. Devices on the network all communicate through a single access point, which is generally the wireless router. For example, let’s say you have two laptops sitting next to each other, each connected to the same wireless network. Even when sitting right next to each other, they’re not communicating directly. Instead, they’re communicating indirectly through the wireless access point. They send packets to the access point — probably a wireless router — and it sends the packets back to the other laptop. Infrastructure mode requires a central access point that all devices connect to.
Ad-hoc mode is also known as “peer-to-peer” mode. Ad-hoc networks don’t require a centralized access point. Instead, devices on the wireless network connect directly to each other. If you set up the two laptops in ad-hoc wireless mode, they’d connect directly to each other without the need for a centralized access point.
Advantages and Disadvantages
Ad-hoc mode can be easier to set up if you just want to connect two devices to each other without requiring a centralized access point. For example, let’s say you have two laptops and you’re sitting in a hotel room without Wi-Fi. You can connect them directly with ad-hoc mode to form a temporary Wi-Fi network without needing a router. The new Wi-Fi Direct standard also builds on ad-hoc mode, allowing devices to communicate directly over Wi-Fi signals.
Infrastructure mode is ideal if you’re setting up a more permanent network. Wireless routers that function as access points generally have higher-power wireless radios and antennas so they can cover a wider area. If you’re using a laptop to set up a wireless network, you’ll be limited by the power of the laptop’s wireless radio, which won’t be as strong as a router’s.
Ad-hoc mode also has other disadvantages. It requires more system resources as the physical network layout will change as devices move around, while an access point in infrastructure mode generally remains stationary. If many devices are connected to the ad-hoc network, there will be more wireless interference — each computer has to establish a direct connection to each other computer rather than going through a single access point. If a device is out of range of another device it wants to connect to, it will pass the data through other devices on the way. Passing the data through several computers is just slower than passing it through a single access point. Ad-hoc networks don’t scale well.
When to Use Each
Deciding when to use each type of network is actually pretty simple. If you’re setting up a wireless router to function as an access point, you’ll want to leave it in infrastructure mode. If you’re setting up a temporary wireless network between a handful of devices, ad-hoc mode is probably fine.
There’s one other big catch here. Many devices don’t support ad-hoc mode because of its limitations. Android devices, wireless printers, Google’s Chromecast, and a wide variety of other Wi-Fi-enabled devices don’t want to deal with the problems of ad-hoc networks and will refuse to connect to them, only connecting to networks in infrastructure mode. There’s not much you can do about this; you just have to use a network in infrastructure mode rather than ad-hoc mode.
Creating Infrastructure Mode Access Points on Your Laptop
You can easily create a local area Wi-Fi network on your laptop, whether you’re using Windows, Mac OS X, or Linux. Unfortunately, most operating systems will create an ad-hoc network by default. For example, you can create an ad-hoc network from the Control Panel in Windows or create an ad-hoc network on your Ubuntu Linux machine. This is fine if you want to connect two laptops, but it’s very inconvenient if you need to connect a device that only supports networks in infrastructure mode.
If you’re using Windows 7 or 8, you can turn your Windows laptop into an infrastructure-mode wireless access point using a few Command Prompt commands. Connectify makes this easier by providing a nice graphical user interface, but it’s actually just using the hidden feature built into Windows 7 and above.
If you need to create an infrastructure-mode access point on Linux, look into the AP-Hotspot tool. On a Mac, enabling the Internet Sharing feature will create a network in infrastructure mode, not ad-hoc mode.
You normally shouldn’t have to worry about these two different network modes. Routers come configured to use infrastructure mode by default, and ad-hoc mode will work for quickly connecting two laptops. If you want to do something a bit fancier on Windows or Linux and set up an infrastructure mode network, you’ll need to use one of the tricks above.