<P> When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters . </P> <P> There are two definitions for wireless LAN roaming: </P> <Ol> <Li> Internal Roaming: The Mobile Station (MS) moves from one access point (AP) to another AP within a home network if the signal strength is too weak . An authentication server (RADIUS) performs the re-authentication of MS via 802.1 x (e.g. with PEAP). The billing of QoS is in the home network . A Mobile Station roaming from one access point to another often interrupts the flow of data among the Mobile Station and an application connected to the network . The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based on proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal . The Mobile Station, however, may lose a connection with an access point before associating with another access point . In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence . </Li> <Li> External Roaming: The MS (client) moves into a WLAN of another Wireless Internet Service Provider (WISP) and takes their services (Hotspot). The user can use a foreign network independently from their home network, provided that the foreign network allows visiting users on their network . There must be special authentication and billing systems for mobile services in a foreign network . </Li> </Ol> <Li> Internal Roaming: The Mobile Station (MS) moves from one access point (AP) to another AP within a home network if the signal strength is too weak . An authentication server (RADIUS) performs the re-authentication of MS via 802.1 x (e.g. with PEAP). The billing of QoS is in the home network . A Mobile Station roaming from one access point to another often interrupts the flow of data among the Mobile Station and an application connected to the network . The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based on proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal . The Mobile Station, however, may lose a connection with an access point before associating with another access point . In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence . </Li>

A service set identifier is the part of a wirelesslan that connects it to other networks