The density of Wi-Fi Access Points (APs)has increased rapidly in urban downtowns and enterprise and campus networks . In most scenarios, a Wi-Fi client has the choice to associate with more than one available AP [3, 12]. Therefore, it is increasingly common to ﬁnd physically near by Wi-Fi clients that are associated with different APs.
A number of applications can beneﬁt from the ability to send and receive information from nearby clients. For example, clients can perform better AP selection if they have knowledge about the performance of clients associated to neighboring APs. Applications such as “buddies near me” can discover clients that are nearby but associated to another AP. Similarly, geo casting  based applications can reach out to more clients in the same region than being limited to only one wireless network.