GSM is a 2G, cellular network that allows mobile phones to connect to the network by locating cells in the local vicinity of the phone. Within a GSM network, there are five cell sizes that have varying coverage areas based on the implementation environment: micro, macro, pico, umbrella, and femto. The macro cells are the larger cells where the base station antenna is typically located above rooftop level on a building or a mast and have much further range than the other cells. Femtocells are those designed for use in small business environments or residential areas, and picocells are small cells that are designed for use inside. The effective horizontal range of a cell depends on a number of factors to include the environment, antenna height, propagation conditions, and antenna gain and can range up to 20 or more miles.
In 3GPP terminology, a Home Node B (HNB) is a 3G femtocell. A Home eNode B (HeNB) is an LTE 4G femtocell.