Mobile architecture
A service area is defined as an area in which a mobile station is
obtainable by another PLMN, PSTN or ISDN subscriber without
the subscriber’s knowledge of the actual location of the mobile
A service area may consist of several PLMNs. One SA may
consist of one country, be a part of a country or comprise
The location registration system associated with each service
area must thus contain a list of all mobile stations located
within that service area.