the present invention provides a method for controlling the overflow of roaming users in a mobile communication system . the method can be applied to any mobile communication system in which roaming numbers are allocated to roaming users before the users access mobile communication functions such as call delivery ( e . g ., the tacs system ). the first embodiment applies the method of the invention to a public mobile communication system , while the second embodiment applies the method of the invention to a private mobile communication system . however , it is understood that this is not intended to limit the scope of the present invention . [ 0069 ] fig8 shows a diagram of the public mobile communication system according to the first embodiment of the present invention . moreover , fig9 shows the flow chart of the overflow registration process of the public mobile communication system according to the first embodiment of the present invention . step 601 : roaming user 38 roams from home network f to network g . step 602 : roaming user 38 delivers the register request to msc 33 . step 603 : msc 33 delivers the register request to vlr 36 . step 604 : vlr 36 determines whether a roaming number is available . if a roaming number is available , go to the step 605 , wherein vlr 36 allocates the roaming number to roaming user 38 . if there are no roaming numbers available , go to the step 606 , wherein vlr 36 assigns a roaming number rn 2 of an inactive roaming user 39 to roaming user 38 . inactive roaming user 39 becomes an overflow roaming user , and the inactive roaming user &# 39 ; s profile is canceled from vlr 36 . the selection of the inactive roaming user 39 can be based on the longest period of inactivity , the earliest registration , random selection , or any other appropriate method . step 607 : vlr 36 notifies hlr 30 that the roaming user 39 is an overflow user and the roaming number rn 2 is allocated to the roaming user 38 . step 608 : hlr 30 registers the roaming number rn 2 of the roaming user 38 and sets up the roaming number overflow column of the roaming user 39 . it is possible that roaming user 38 and roaming user 39 do not come from the same home network . fig1 shows a diagram of the public mobile communication system according where roaming user 38 comes from home network f while roaming user 39 comes from home network k . in this case , in step 607 , vlr 36 notifies hlr 30 that the roaming number rn 2 is allocated to the roaming user 38 and notifies hlr 32 in network k that the roaming user 39 is an overflow user . in step 608 , hlr 32 sets up the roaming number overflow column of the roaming user 39 . as described above , the method of this invention assigns the roaming number of an inactive roaming user to a newly arriving roaming user . the inactive roaming user then becomes an overflow roaming user . should the overflow roaming user require the use of the mobile communication functions , for example to make or receive a call , the overflow roaming user must be re - registered . the following describes the situation where overflow roaming user 39 receives a telephone call , wherein fig1 shows the flow chart of the overflow user call delivery process of the public mobile communication system according to the first embodiment of the present invention . in this example , network f is the home network of roaming user 39 and roaming user 40 . step 701 : when a telephone user dials the telephone number of the overflow roaming user 39 , the call request is connected to gmsc 35 in the home network of the roaming user 39 . step 702 : gmsc 35 asks hlr 30 to provide the routing information of the roaming user 39 . step 703 : hlr 30 asks vlr 36 to provide a roaming number for the roaming user 39 . step 704 : vlr 36 determines whether a roaming number is available . if a roaming number is available , go to the step 705 , wherein vlr 36 allocates the roaming number to roaming user 39 . if there are not roaming number available , go to the step 706 , vlr 36 assigns a roaming number rn 3 of an inactive roaming user 40 to roaming user 39 . inactive user 40 becomes an overflow roaming user , and the inactive roaming user &# 39 ; s profile is canceled from vlr 36 . the selection of the inactive roaming user 40 can be based on the longest period of inactivity , the earliest registration , random selection , or any other appropriate method . as can be seen , inactive roaming user 40 takes the place of roaming user 39 as an overflow roaming user . step 707 : vlr 36 notifies hlr 30 that the roaming user 40 is an overflow user and the roaming number rn 3 is allocated to the roaming user 39 . step 708 : hlr 30 registers the roaming number rn 3 of the roaming user 39 and sets up the roaming number overflow column of the roaming user 40 . as described above , if the roaming user 39 and the roaming user 40 belong to different networks ( for example , if roaming 39 belongs to home network f while roaming user 40 belongs to home network k ), in step 607 , vlr 36 notifies hlr 30 that the roaming number rn 3 is allocated to the roaming user 39 and notifies hlr 32 in network k that the roaming user 40 is an overflow user . in step 608 , hlr 32 sets up the roaming number overflow column of the roaming user 40 . step 709 : hlr 30 delivers the roaming number rn 3 to gmsc 35 . step 710 : gmsc 35 connects gmsc 37 with roaming number rn 3 . step 711 : gmsc 37 asks vlr 36 provides more detail routing information of the roaming user 39 . step 712 : vlr 36 notifies gmsc 37 the routing information of the roaming user 39 . step 713 : gmsc 37 finishes the operation of connecting to the roaming user 39 . as long as the number of the roaming users being called at the same time does not exceed the number of roaming users of the vlr 36 , the system can handle all of the roaming users with a smaller number of roaming numbers . thus , the efficiency of the present invention is better than the prior art . by the method according to the present invention , the performance of a conventional system can be improved with without upgrading the hardware . [ 0093 ] fig8 shows a diagram of the private mobile communication system according to the second embodiment of the present invention . the roaming numbers available in a specific zone of a pbx are limited . if there are some activity causing users to gather to in a specific zone , the specific zone will not have enough roaming numbers . thus , roaming users in the specific zone cannot register , and cannot use the mobile communication functions . the second embodiment of the present invention provides a method to control the overflow roaming numbers to higher the performance of the private mobile communication system . [ 0095 ] fig9 shows the flow chart of the overflow registration process of the private mobile communication system according to the second embodiment of the present invention . step 801 : roaming user 48 roams from home zone h to zone j and registers to mm 42 . step 802 : mm 42 determines whether a roaming number is available . if a roaming number is available , go to the step 803 , wherein mm 42 allocates the roaming number rn 4 to roaming user 48 . if there are no roaming numbers available , go to the step 804 , wherein mm 42 assigns a roaming number of an inactive roaming user 49 to roaming user 48 , wherein the inactive roaming user 49 becomes an overflow roaming user and the inactive roaming user &# 39 ; s profile is canceled from mm 42 . the selection of the inactive roaming user 49 can be based on the longest period of inactivity , the earliest registration , random selection , or any other appropriate method . step 805 : mm 42 notifies mm 41 that the inactive roaming user 49 is an overflow user and the roaming number rn 4 is allocated to the roaming user 48 whom is in zone j . step 806 : mm 41 updates the routing information and the roaming number of the roaming user 48 , sets up roaming number overflow column of the roaming user 49 , stores the routing information of the roaming user 48 and changes the unconditional diverted number to rn 4 as in step 304 , and cancels the set of the unconditional diverted number of user 49 . step 807 : mm 41 delivers the registration acknowledged message to mm 42 indicating the mm 41 has received the information that the roaming user 20 has moved to zone j , wherein the message further comprises the profile of the user . step 808 : when mm 42 receives the registration acknowledged message , mm 42 responds that the roaming user 48 has completed the registration request . in step 802 , if the user 48 and the user 49 are from different zone ( e . g ., the home zone of the user 49 is zone i ), mm 42 notifies mm 41 that the roaming number rn 4 is allocated to the roaming user 48 whom is in zone j and notifies mm 43 that the inactive roaming user 49 is an overflow user . moreover , in step 806 , mm 41 updates the routing information and the roaming number of the roaming user 48 , stores the routing information of the roaming user 48 and changes the unconditional diverted number to rn 4 , while mm 43 sets up roaming number overflow column of the roaming user 49 , and cancels the set of the unconditional diverted number of user 49 as in step 304 . the following described the situation wherein the telephone number of the roaming user 48 , who is an overflow user , is dialed . refer to fig1 , which shows the flow chart of the overflow call delivery process of the private mobile communication system according to the second embodiment of the present invention . step 901 : the telephone number of the overflow roaming user 48 is dialed , wherein the telephone number is the extension number of the roaming user 48 in zone h . step 902 : mm 41 delivers the routing information request message to ask mm 42 to provide a roaming number , wherein the routing information request message further comprises the user profile of the overflow roaming user 48 . step 903 : mm 42 allocates a roaming number of an inactive roaming user 49 to overflow roaming user 48 , wherein the inactive roaming user becomes an overflow user and the inactive roaming user &# 39 ; s profile is canceled from mm 42 . the selection of the inactive roaming user 49 can be based on the longest period of inactivity , the earliest registration , random selection , or any other appropriate method . step 904 : mm 42 responds to mm 41 that the roaming number of the user 48 is rn 5 and the user 49 is an overflow user . mm 42 further updates the user information and sets up the divert information . step 905 : mm 41 asks pbx 45 connecting to pbx 44 with rn 5 . step 906 : pbx 44 receives the call request of the pbx 45 . a . if the interface is line , pbx 44 rings the line , and the ring will be detected by mm 42 . b . if the interface is trunk , pbx 44 performs the call request with m 42 by signaling . step 907 : when mm 42 detects the ring or receives the signaling request , connects the roaming user 48 and the 5 dialing user to establish the calling . the foregoing description of the preferred embodiments of this invention has been presented for purposes of illustration and description . obvious modifications or variations are possible in light of the above teaching . the embodiments were chosen and described to provide the best illustration of the principles of this invention and its practical application to thereby enable those skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated . all such modifications and variations are within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly , legally , and equitably entitled .