Ad-Hoc and Infrastructure Modes

When architecting an 802.11 network, there are two modes in which you can operate: Ad-Hoc and Infrastructure. In Ad-Hoc mode (see image above), sometimes called “IBSS” or “Independent Basic Services Set”, all devices operate in a peer-to-peer mode.There are no access points used in this topology, as all devices communicate directly with all other devices.
In Infrastructure mode, an AP is connected to a wired infrastructure (such as Ethernet) and all of the wireless devices communicate with the AP. Even if two wireless devices are located right next to each other, all communication between the devices occurs through an AP. When using Infrastructure mode, a collection of wireless devices connected to an AP is referred to as a Basic Service Set (BSS).
If two or more BSSs are connected together using a “Distribution System” (such as wired Ethernet), the collection of BSSs is referred to as an Extended Service Set (ESS).