Computers and other devices that support Wi-Fi can connect to two primary types of network: access point, also called infrastructure, and ad hoc. Most of the time, a "Wi-Fi connection" refers to an access point connection, where a computer connects to a local area network and the Internet using a wireless router. Ad hoc connections do not require a router, and can connect multiple devices to one another directly.
Access Point Networks
In infrastructure mode, every wireless device uses its Wi-Fi radio to link up with a central access point -- usually a wireless router in home networks. The router often has a wired connection to a modem or includes a built-in modem, and provides an Internet connection to all linked devices. These devices can also communicate with one another via a local area network that runs through the router.
Ad Hoc Networks
Ad hoc networks connect multiple devices directly via Wi-Fi. To set up an ad hoc network, one device begins transmitting a network ID and listens for incoming connections. As other devices connect, the machines form a network among themselves, processing data routing internally instead of relying on a router. Ad hoc networks can include an Internet connection that is shared by one of the linked devices -- tethering a smartphone, for example -- but are generally used for local networking.
Advantages to Ad Hoc Networks
By not requiring a router, ad hoc networks allow file sharing and other data connections to take place anywhere you have two machines. Even when a router is available, you may not have control over its network settings, such as at a public hotspot or in an office. Ad hoc networks let you set up your own temporary, private connection without changing any existing network options. Ad hoc also provides a security benefit: you can pick a unique password while setting up the network, rather than giving out an existing network password.
Advantages to Access Point Networks
Connecting to an existing infrastructure network requires almost no setup, and usually provides the benefit of an Internet connection. Conversely, ad hoc networks often require a complicated setup process -- though users on Windows 7 could create an ad hoc network through the Network and Sharing Center, this feature no longer exists on Windows 8. Instead, setting up an ad hoc network requires using the command prompt. Not all Wi-Fi hardware supports the creation of ad hoc networks, further limiting their ease of use.
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