location for a service affects If the frequency assignments causing and suffering interference the treatment that a station of that service receives if inter- fall within the scope of an internationally agreed frequency allot- ference should arise. ment or frequency assignment plan, the interference may have The international frequency allocations are not uniform world- arisen because system parameters assumed in planning have not wide. Three geographical regions have been defined (ITU, been implemented; if so, the remedy is to bring the systems into line 1990, para 392-399) and in some frequency bands there are with the plan. Otherwise, it may be necessary to revise the plan to different allocations in the different regions. The regions are eliminate the interference. However, if the assignment suffering approximately as follows: interference is operating in accordance with a plan and the interfer- Region 1: Europe, Africa, USSR in Asia, Mongolia and Asian ing assignment, having been made by another administration which countries to the West of the Persian Gulf. has ratified the plan, had not been planned, then the interfering Region 2: North and South America. assignment will be withdrawn. Region 3: The parts of Asia not in Region 1, plus Australasia. Few frequency bands are allocated internationally for only one Footnotes to the international table of frequency allocations service; most bands are shared by at least two services, and some by provide for departures from the world wide or regional alloca- several; see Section 26.3.1. The services sharing a band may have tions in various specified countries. See Section 26.5 below. equal allocation status, but in other bands some allocations have primary status, and others have secondary status. Thus, station "S", of a service having secondary allocation status must stop using an The frequency bands allocated to the various radio services and assignment that causes harmful interference to station "P", belong- the methods which are applied internationally by regula