Extended Service Set (ESS) is created by connecting multiple Basic Service Set (BSS) via a distribution system. Two or more Access Points are connected to the same Local Area Network to provide a larger coverage area which allows the client to move from one AP to another AP and still be the part of the LAN. This process is known as roaming in which a client can physically change locations and still be connected to the LAN. When a client senses that radio signal from the current AP are getting weaker, it finds a new AP with stronger signals starts using that AP. An ESS generally includes a common SSID to allow roaming from access point to access point without requiring client re-conï¬guration.
The wireless coverage area created by joining two or more Access Points via distribution system is called an Extended Service Area (ESA). Stations within the same ESA may communicate with each other, even though these stations may be in different basic service areas and may even be moving between basic service areas, this requires that the wireless medium and the backbone of the ESS must be layer 2 link.
A Distribution System connects multiple Access Points to form an ESS, while doing so it provides the wireless stations with the option of mobility. It is the means by which an access point communicates with another access point to exchange frames for stations in their respective BSSs, forward frames to follow mobile stations as they move from one BSS to another, and exchange frames with a wired network.
