In some cases, the distance between the two locations to be connected exceeds the range of a single wireless link. This may be the case when the distance between the APs exceeds the radio range, or when obstacles block the line of site between the two APs.
In these cases, the two end points can be connected by stringing together multiple APs, each of which has two WLAN modules. Because the intermediate APs often operate solely as relay stations, the operating mode of these APs is referred to as "relay mode".