Mobile communications system and communications network

A mobile communications system including a plurality of communications networks, each of which has one location register (a home location register or gate location register) and one or more visitor registers. Each of the visitor registers is located in each one of visiting areas for storing information about a communication terminal. The location register stores the number of the visitor register of the visiting area in which the communication terminal is present, and the information about the communication terminal. When the communication terminal moves between the communications networks, the information about the communication terminal is transferred between the location registers. When the communication terminal moves between the visiting areas in the same communications network, the information about the communication terminal is provided from the location register to the visitor register. When the communication terminal moves within the same visiting area, the information about the communication terminal can be obtained from the visitor register. This makes it possible to reduce the traffic on the common control line between the communications networks and in the communications network.

TECHNICAL FIELD 
The present invention relates to a mobile communications system and a 
communications network capable of reducing traffic on common control lines 
in and between networks. 
BACKGROUND ART 
Two systems are widely known as conventional mobile communications systems: 
GSM (Global System for Mobile communications) mainly used in Europe; and 
PDC (Personal Digital Cellular) used in Japan and the U.S. 
FIG. 1 shows a GSM system. There are provided a plurality of visiting areas 
50, 51 and 52 in networks 10 and 11 offered by common carriers, and 
communication terminals 60 communicate while moving in the visiting areas. 
The visiting areas 50, 51 and 52 include visitor location registers 30, 31 
and 32, respectively. These registers are connected to the communication 
terminals 60, which are present in the visiting areas, through switching 
machines 41, 42 and 43, and manage information about the terminals. 
The visitor location registers 30-32 are further connected to a home 
location register 20 through common control lines. The home location 
register 20 stores the numbers of the visitor location registers, which 
indicate areas the communication terminals 60 are visiting, and 
information about the communication terminal. Each communication terminal 
is registered in advance in a predetermined home location register. 
When the communication terminal 60 is present in the visiting area 50, 
information about the communication terminal is sent from the home 
location register 20 to the visitor location register 30 to be stored, and 
the number of the visitor location register 30 is stored in the home 
location register 20. When the communication terminal 60 moves from the 
visiting area 50 in the communications network 10 to the visiting area 51 
in the communications network 11, the communication terminal 60 carries 
out a position registration in the home location register 20 through the 
switching machine 42. 
FIG. 2A illustrates the location registration. When the communication 
terminal 60 enters the visiting area 51, and sends a location registration 
signal to the switching machine 42, the visitor location register 31 
carries out the location registration of the communication terminal 60. 
Specifically, the visitor location register 31 sends to the home location 
register 20 the communication terminal number and visitor location 
register number associated with the communication terminal 60. The home 
location register 20 rewrites the visitor location register number from 30 
to 31, and requires the visitor location register 30 to delete the 
information about the communication terminal 60. Besides, it sends the 
information about the communication terminal 60 to the visitor location 
register 31. Subsequently, the location registration signal is sent back 
from the home location register 20 to the communication terminal 60 
through the visitor location register 31 and switching machine 42, thus 
completing the location registration. 
When the communication terminal 60 further moves from the visiting area 51 
to the visiting area 52 within the same communications network 11, the 
processing similar to that of FIG. 2A is carried out. That is, a similar 
processing is performed in which the switching machine 42, visitor 
location register 31 and visitor location register 30 are replaced by the 
switching machine 43, visitor location register 32 and visitor location 
register 31, respectively. 
FIG. 2B illustrates the processing procedure of a call connection occurred 
while the communication terminal 60 is present in the visiting area 51. A 
call to the communication terminal 60 is connected to the switching 
machine 40 linked to the home location register 20. The switching machine 
40 inquires of the home location register 20 the location of the 
communication terminal 60. The home location register 20 inquires of the 
visitor location register 31 the location of the communication terminal 60 
using the visitor location register number stored in the home location 
register 20 as the information about the communication terminal 60. The 
visitor location register 31 provides the communication terminal 60 with a 
temporary call connection number which is sent to the switching machine 40 
through the home location register 20. The switching machine 40 connects 
the call to the switching machine 42 in response to the temporary call 
connection number, and the switching machine 42 connects the call to the 
communication terminal 60. 
FIG. 3 shows the PDC system. In this system, the switching machine 41 
associated with the visiting area 50 in the communications network 10 is 
directly connected to the home location register 20 through the common 
control line. Likewise, the switching machines 42 and 43 associated with 
the visiting areas 51 and 52 in the communications network 11 are directly 
connected to the gate location register 21 through the common control 
lines. In other words, in the PDC system, the visitor location registers 
30-32 are obviated which are provided in the GSM system, and the gate 
location register 21 is provided in the communications network, excluding 
in the communications network which is provided with the home location 
register 20. Although the visiting areas have one to one correspondence 
with the switching machines in this figure, this is not essential. 
When the communication terminal 60 is in the communications network 10 
including the home location register 20 (that is, in the home 
communications network), the home location register 20 stores the number 
of the visiting area in which the communication terminal 60 is present, 
and the number of the switching machine the communication terminal 60 used 
last, in addition to the number and information about the communication 
terminal 60. 
On the other hand, when the communication terminal 60 is in the 
communications network 11 other than the home communications network (that 
is, in the visiting communications network), the home location register 20 
stores the number of communications network indicating the communications 
network 11 in which the communication terminal 60 is present, and the 
information about the communication terminal 60. The gate location 
register 21 in the communications network 11 stores the information about 
the communication terminal 60, the number of visiting area in which the 
communication terminal 60 is present, and the number of switching machine 
the communication terminal 60 used last. In addition, the gate location 
register 21 stores the communication terminal numbers of individual 
subscriber terminals, communication terminal information, the numbers of 
the switching machines and the visiting area numbers in the communications 
network 11. 
When the communication terminal 60 moves from a visiting area not shown in 
FIG. 3 to the visiting area 50, or moves in the visiting area 50, and 
sends a location registration signal to the switching machine 41, the 
location of the communication terminal 60 (the visiting area number) is 
stored in the home location register 20. 
FIG. 4A illustrates the procedure of a first location registration when the 
communication terminal 60 moves from the visiting area 50 in the 
communications network 10 to the visiting area 51 in the communications 
network 11. 
When the communication terminal 60 enters the visiting area 51 and sends 
the location registration signal to the switching machine 42, the 
switching machine 42 carries out the location registration of the 
communication terminal 60 to the home location register 20 through the 
gate location register 21. More specifically, when the switching machine 
42 sends to the gate location register 21 the communication terminal 
number, switching machine number and visiting area number of the 
communication terminal 60, the gate location register 21 in turn sends to 
the home location register 20 the number of the communication terminal 60, 
the number of the communications network 11 and the call connection number 
used for a call connection from the communications network 10 to the 
communications network 11. After storing these data, the home location 
register 20 sends the location registration signal back to the gate 
location register 21, and then the gate location register 21 sends a 
location registration response signal back to the communication terminal 
60 via the switching machine 42, thereby completing the location 
registration. 
FIG. 4B illustrates the procedure of a location registration processing 
when the communication terminal 60 moves within the same communications 
network 11, that is, when the communication terminal 60 moves within the 
visiting area 52 in the communications network 11, or moves from the 
visiting area 51 to the visiting area 52. 
When the communication terminal 60, which is present in the visiting area 
52, sends the location registration signal to the switching machine 43, 
the switching machine 43 sends to the gate location register 21 the 
communication terminal number, switching machine number and visiting area 
number associated with the communication terminal 60. Having stored these 
data, the gate location register 21 sends back the location registration 
response signal to the communication terminal 60 via the switching machine 
43, thereby completing the location registration. In this case, the home 
location register 20 is not updated. 
FIG. 5 illustrates the processing procedure of a call connection occurred 
while the communication terminal 60 is in the visiting area 52. The call 
to the communication terminal 60 is first connected to the switching 
machine 41 linked to the home location register 20. The switching machine 
41 inquires of the home location register 20 the communication terminal 
location. The home location register 20 sends back a call connection 
number indicating the location of the communication terminal 60. The 
switching machine 41 connects the call to the switching machine 42 by 
using this call connection number. The switching machine 42 inquires of 
the gate location register 21 the information about the communication 
terminal, reads the location of the communication terminal 60, and 
connects the call to the switching machine 43. The switching machine 43 
connects the call to the communication terminal 60 in the visiting area 
52. 
When the communication terminal 60 is in the communications network 10, the 
location of the communication terminal 60 is stored in the home location 
register 20. In this case, the switching machine 41 connects the call to a 
switching machine covering the location. Then, the switching machine 
connects the call to the communication terminal 60 in the visiting area 
the switching machine covers. 
The foregoing GSM as shown in FIGS. 1, 2A and 2B has the following 
drawbacks. 
(1) When the communication terminal 60 moves to another visiting area even 
in the same communications network, the home location register 20 must be 
updated as illustrated in FIG. 2A. Therefore, when the communication 
terminal 60 moves to another visiting area in the communications network 
other than the home communications network, as moving from the visiting 
area 51 to visiting area 52, it becomes necessary to update the home 
location register 20 in other communications network. This will increase 
the traffic on the common control line between the communications 
networks. 
(2) When increasing a new visitor location register in a communications 
network, it is required for the new visitor location register to be 
accessed from the other communications networks. 
On the other hand, the PDC system as shown in FIGS. 3-5 is provided with a 
home location register or a gate location register (these are called 
location registers in common) for each communications network to store the 
information about each communication terminal. Therefore, it is not 
necessary to update the information of the home location register in other 
communications network when the communication terminal moves within the 
same communications network, in which case only the location register in 
that communications network is updated. This will reduce the traffic 
between the communications networks. 
It is necessary, however, for such an arrangement to send the communication 
terminal information from the location register to the switching machine 
at a calling or a call connection. This will increase the traffic on the 
common control lines in the same communications network, thereby causing 
delay of the calling and call connection. In particular, the drawback 
cannot be ignored when the switching machine is located far from the 
location register. 
DISCLOSURE OF THE INVENTION 
The object of the present invention is to provide a mobile communications 
system and communications network that can reduce the traffic within and 
between the communications networks. 
In a first aspect of the present invention, there is provided a mobile 
communications system including a plurality of communications networks, 
and a communication terminal which moves in and between one or more 
visiting areas in the communications networks, and carries out a location 
registration in a current visiting area, the mobile communications system 
comprising: 
a location register located in each of the communications networks for 
storing information about the communication terminal and a visiting area 
in which the communication terminal is present, when the communication 
terminal enters the communications network in which the location register 
is located from another communications network, and carries out the 
location registration; and 
a visitor register located in each of the visiting area for receiving 
information about the communication terminal sent from the location 
register in the communications network, and for storing the information 
about the communication terminal, when the communication terminal moves to 
the visiting area in which the visitor register is located from another 
visiting area in the same communications network. 
Here, the location register may be a home location register located in a 
home communications network, in which the communication terminal is 
registered in advance, for storing the information about the communication 
terminal. 
The location register may be a gate location register located in a visitor 
communications network different from the home communications network, for 
receiving the information about the communication terminal from the home 
location register and for storing the information, when the communication 
terminal moves from the home communications network to the visitor 
communications network. 
In a second aspect of the present invention, there is provided a mobile 
communications network including one or more visiting areas, wherein a 
communication terminal moves in and between the visiting areas, and 
carries out a location registration in a current visiting area, the mobile 
communications network comprising: 
a location register for storing information about the communication 
terminal and a visiting area in which the communication terminal is 
present, when the communication terminal carries out the location 
registration; and 
a visitor register located in each of the visiting areas for receiving the 
information about the communication terminal sent from the location 
register and for storing the information, when the communication terminal 
moves in from another visiting area. 
The mobile communications network may be a home communications network in 
which the communication terminal is registered in advance, and the 
location register is a home location register for continually storing the 
information about the communication terminal. 
The mobile communications network may be a visitor communications network 
different from a home communications network in which the communication 
terminal is registered in advance, and the location register may be a gate 
location register for receiving the information about the communication 
terminal from the location register of the home communications network and 
for storing the information, when the communication terminal moves from 
the home communications network to the visitor communications network. 
The visitor register may further comprise: 
a first timer means for counting a time period after having been reset when 
a call connection occurs to the communication terminal; and 
means for registering in the location register a number of the visitor 
register of the visiting area in which the communication terminal is 
present, when the communication terminal carries out a location 
registration after the first timer has counted a predetermined first time 
period. 
The visitor register may further comprise: 
a second timer means for counting a time period after having been reset 
when communications occurs between the communication terminal and the 
visitor register; and 
means for deregistering the information about the communication terminal 
stored in the visitor register, when the second timer means has counted a 
predetermined second time period. 
According to the present invention, it is possible to reduce the traffic on 
the common control lines between the home communications network in which 
the home location register is located and the communications networks 
(visiting communications networks) other than the home communications 
network. It is also possible to reduce the traffic on the common control 
lines between the visitor registers and the location register in the same 
communications network. 
Furthermore, using the first timer information makes it possible to correct 
the inconsistency of information between the visitor registers and the 
location register. Moreover, using the second timer information makes it 
possible to automatically delete from the visitor register the information 
about the communication terminal which is absent in that visiting area. 
These will be described in more detail in the following embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION 
An embodiment in accordance with the present invention will now be 
described with reference to the accompanying drawings. 
FIG. 6 is a block diagram showing a configuration of an embodiment of a 
mobile communications system in accordance with the present invention. 
This embodiment mainly differs from the conventional PDC system in the 
following: 
(1) The switching machines 41-43 are provided with visitor registers 70-72, 
respectively. Specifically, the visitor register 70 is added to the 
switching machine 41 for storing the communication terminal information 
and communication terminal numbers. Likewise, the visitor register 71 is 
added to the switching machine 42, and the visitor register 72 is added to 
the switching machine 43. 
The visitor registers 70-72 have a configuration simpler than that of the 
visitor location registers 30-32 of the GSM system as shown in FIG. 1. It 
is necessary for the visitor location registers 30-32 of the GSM system to 
preserve the integrity of the stored data. In other words, they must be 
provided with measures to backup by restart or the like against potential 
loss of data, or to reconstruct data between the home location register 
and the visitor location registers. In contrast with this, it is 
sufficient for the visitor registers 70-72 of this embodiment to store 
plain copies of the data in the location registers, and to make copies of 
the data from the location registers again if the data is lost. 
(2) The visitor register 70 includes a plurality of pairs of timer 
information 70A and 70B, each of which is provided in connection with each 
communication terminal present in the visiting area. Similar timer 
information 71A and 71B is provided in the visitor register 71, and timer 
information 72A and 72B is provided in the visitor register 72. The timer 
information is used for handling mismatches of data between the location 
registers and visitor registers. 
In FIG. 6, the home location register 20 stores the information about the 
communication terminal 60 which subscribes to the communications network 
10. In addition, when the communication terminal 60 is present in the 
visiting area 50 in the communications network 10, the home location 
register 20 stores the number of the visiting area 50 and the number of 
the switching machine 41 thereof. When the communication terminal 60 is 
present in the visiting area in the communications network 11, the home 
location register 20 stores the number of the communications network 11 
and a call connection number used for connecting a call from the 
communications network 10 to the communications network 11. 
The gate location register 21 stores the information about the 
communication terminal 60 in the communications network 11, the number of 
the visiting area in which the communication terminal 60 is present, and 
the number of the switching machine of the visiting area. 
FIG. 7 is a block diagram showing a configuration of the visitor register 
71 (70, 72). The visitor register is usually arranged with a computer like 
a workstation. The visitor register 71 comprises a controller 81, a memory 
83, a timer 85 and a common control line device 87. The common control 
line device 87 is connected to the switching machine through the common 
control line. 
The memory 83 stores for each number of the communication terminals in the 
visiting area, the communication terminal information, the first timer 
information 71A and the second timer information 71B. The controller 81 
updates timer information in response to the information fed from the 
timer 85. 
The first timer information 71A is provided as a measure against a 
potential error of the information about the communication terminal 60, 
which is stored in the gate location register 21. The visitor register 71 
decides that the information about the communication terminal 60, which is 
stored in the gate location register 21, is erroneous if a call connection 
to the communication terminal 60 does not occur for more than a fixed time 
T.sub.1. In this case, the visitor register 71, receiving a location 
registration request from the communication terminal 60, commands the gate 
location register 21 to rewrite the information therein in accordance with 
the contents of the visitor register 71. The first timer information is 
used for counting the fixed time T.sub.1. 
The second timer information 71B, on the other hand, is provided for 
deleting the information about the communication terminal 60 remaining in 
the visitor register 71 even after the communication terminal 60 has moved 
from the visiting area 51 to another visiting area. Specifically, if there 
occurs no location registration signal or calling from the communication 
terminal 60, or no call connection to the communication terminal 60 for 
more than a fixed time T.sub.2, the visitor register 71 decides that the 
communication terminal 60 has left the visitor register, and deletes the 
information about the communication terminal 60. The second timer 
information 71B is used to count this fixed time T.sub.2. The second timer 
information 71B is reset when the first timer information 71A expires, 
when a call connection to the communication terminal occurs, or when the 
location registration request or calling from a communication terminal 
occurs, and after the reset, it is updated by the information from the 
timer 85. 
FIG. 8A illustrates a first location registration procedure when the 
communication terminal 60 moves from the communications network 10 to the 
communications network 11. 
When the communication terminal 60 moves from the visiting area 50 in the 
communications network 10 to the visiting area 51 in the communications 
network 11, and sends the location registration signal to the switching 
machine 42, the switching machine 42 accesses to the visitor register 71. 
If the information about the communication terminal 60 is not stored in 
the visitor register 71, the switching machine 42 sends the gate location 
register 21 a location registration signal including the number of the 
communication terminal 60, the number of the switching machine 42, and the 
number of the visiting area 51. The gate location register 21, receiving 
the location registration signal, sends the home location register 20 the 
location registration signal including the number of the communication 
terminal 60, the number of the communications network 11 and the call 
connection number only when the gate location register 21 does not store 
the number of the communication terminal 60. 
The home location register 20, receiving the location registration signal, 
stores the number of the communications network 11 and the call connection 
number, and sends back to the gate location register 21 a location 
registration response including the information about the communication 
terminal 60. The gate location register 21, receiving the location 
registration response, stores the number of the communication terminal 60, 
the number of the visiting area 51 of the communication terminal 60, the 
number of the switching machine 42 of the visiting area 51 and the 
information about the communication terminal 60, and sends back to the 
switching machine 42 the location registration response including the 
information about the communication terminal 60. The switching machine 42, 
receiving the location registration response, registers the communication 
terminal number and information about the communication terminal 60 in the 
memory 83 in the visitor register 71. 
FIG. 8B illustrates a procedure when the communication terminal 60, moving 
in the visiting area 51, carries out a second and the following location 
registrations. The switching machine 42 receives the location registration 
signal from the communication terminal 60, and accesses the visitor 
register 71. This time, at which the first location registration has been 
completed, since the memory 83 of the visitor register 71 stores the 
information about the communication terminal 60, the switching machine 42 
immediately sends back the location registration response to the 
communication terminal 60. 
In this case, if the memory 83 of the visitor register 71 stores the number 
of the communication terminal 60, and the first timer information 71A of 
the communication terminal 60 has not yet expired, it is unnecessary to 
update the contents of the gate location register 21 associated with the 
communication terminal 60. This is because the information about the 
communication terminal 60 stored in the gate location register 21 is 
estimated to be correct if the first timer information 71A has not yet 
expired. On the contrary, if the first timer information 71A has expired 
which is associated with the communication terminal 60 and stored in the 
visitor register 71, the following processing is carried out as shown in 
FIG. 8C. 
FIG. 8C illustrates the procedure of the location registration when the 
communication terminal 60 moves between the visiting areas in the 
communications network 11, or when the first timer information has 
expired. 
When the communication terminal 60 moves from the visiting area 51 to the 
visiting area 52 in the communications network 11, and the switching 
machine 43 receives the location registration signal, the switching 
machine 43 accesses the visitor register 72. If the memory 83 of the 
visitor register 72 does not store the number of the communication 
terminal 60, the switching machine 43 sends the gate location register 21 
the location registration signal including the number of the communication 
terminal 60, the number of the switching machine 43 and the number of the 
visiting area 52. The gate location register 21, when storing the number 
of the communication terminal 60 and receiving the location registration 
signal, sends a communication terminal information deregistration signal 
to the visitor register 71 in the visiting area 51 in which the 
communication terminal 60 was previously present. The gate location 
register 21 also stores the number of the switching machine 43 and the 
number of the visiting area 52, and sends back to the switching machine 43 
the location registration response including the information about the 
communication terminal 60. 
The visitor register 71, receiving the communication terminal information 
deregistration signal, deletes the communication terminal number and 
information about the communication terminal 60 which are stored in the 
visitor register 71. On the other hand, the switching machine 43 which 
receives the location registration response, writes the number and 
information about the communication terminal 60, and sends the location 
registration response back to the communication terminal 60. In this case, 
it is unnecessary to rewrite the contents of the home location register 
20. 
Similar processing is carried out when the location registration occurs 
after the first timer information has expired. More specifically, the 
switching machine 43 decides that the information about the communication 
terminal 60, stored in the gate location register 21 is incorrect. Then 
the switching machine 43 sends the gate location register 21 the location 
registration signal, and resets the first timer information 72A. The 
location registration signal includes the number of the communication 
terminal 60, the number of the switching machine 43 and the number of the 
visiting area 52. The gate location register 21 updates the information 
about the communication terminal 60 using the location registration 
signal. Thus, the correct information about the communication terminal 60 
is stored in the gate location register 21. 
FIG. 9 illustrates a procedure of a call connection processing to the 
communication terminal 60 in the visiting area 52. A call to the 
communication terminal 60 is first connected to the switching machine 41 
in the communications network 10 in which the home location register 20 is 
provided. The switching machine 41 inquires of the home location register 
20 the location of the communication terminal. The home location register 
20 sends the communication terminal location back to the switching machine 
41 in the form of a call connection number. The switching machine 41 
extends the line to the switching machine 42 in the communications network 
11 by using the call connection number. 
The switching machine 42 inquires of the gate location register 21 the 
communication terminal location using the call connection number. The gate 
location register 21 sends back to the switching machine 42 the number of 
the communication terminal 60 and the number of the switching machine 43 
of the visiting area 52 in which the communication terminal 60 is present. 
The switching machine 42 extends the line to the switching machine 43 
using the number of the switching machine 43 which has been received. The 
switching machine 43 accesses the visitor register 72. 
If the visitor register 72 stores the information about the communication 
terminal 60, the switching machine 43 connects the line to the 
communication terminal 60. In this case, if the first timer information 
72A has expired, and the second timer information 72B is acting, the first 
timer information 72A and the second timer information 72B are reset. This 
is because the correct connection of the call proves that the information 
about the communication terminal 60 which is stored in the gate location 
register 21 is correct, and that the communication terminal 60 is present 
in the visiting area 52. 
On the other hand, if the information about the communication terminal 60 
is not stored in the visitor register 72, the switching machine 43 reads 
the information about the communication terminal 60 from the gate location 
register 21, and registers the communication terminal information and 
communication terminal number to the visitor register 72, followed by the 
connection of the communication terminal 60 to the line. When the 
connection to the communication terminal 60 has been completed, the 
switching machine 43 resets the first timer information 72A and the second 
timer information 72B of the visitor register 72. This is because, in this 
case also, the correct connection of the call proves that the information 
about the communication terminal 60 which is stored in the gate location 
register 21 is correct, and that the communication terminal 60 is present 
in the visiting area 52. 
According to the present invention, the following advantages can be gained: 
(1) First, let us compare the present invention with the GSM system as 
shown in FIGS. 1, 2A and 2B. In the GSM system, when the communication 
terminal 60 moves from the visiting area 51 to the visiting area 52 in the 
communications network 11, the visitor location registers 32 and 31 
operates in the same manner as the visitor location registers 31 and 30 of 
FIG. 2A. Thus, the visitor location register 32 must communicate with the 
home location register 20 to obtain the communication terminal 
information. 
In contrast, according to the present invention, when the communication 
terminal 60 moves from the visiting area 51 to the visiting area 52, the 
switching machine 43 can obtain the communication terminal information 
from the gate location register 21 in the same communications network 11 
as shown in FIG. 8C. This can obviate the communications with the home 
location register 20 in the communications network 10. Thus, the present 
invention can reduce the traffic on the common control line between the 
communications networks 10 and 11. This is particularly effective in such 
a case as the communications network 10 is located in Europe and the 
communications network 11 is located in Japan. 
(2) Next, let us compare the present invention with the PDC system as shown 
in FIGS. 3-5. When the communication terminal 60 moves in the visiting 
area 51 in the communications network 11 in the PDC system, the switching 
machine 42 operates in the manner as shown FIG. 4A. This means that the 
switching machine 42 must communicate with the gate location register 21 
to obtain the communication terminal information. 
In contrast, according to the present invention, when the communication 
terminal 60 moves within the visiting area 51, it is enough for the 
switching machine 42 only to access the visitor register 71 connected 
thereto as shown in FIG. 8B. Thus, the present invention can reduce the 
traffic on the common control line between the switching machine and the 
gate location register 21. This is particularly effective when the 
switching machine is located far from the gate location register 21. 
(3) The present invention can correct the inconsistency that could occur 
between the information in the visitor register about the communication 
terminal, and that in the gate location register 21. Specifically, the 
inconsistency can be corrected (a) if there is no communication terminal 
information in the visitor register designated by the gate location 
register, or (b) when the gate location register 21 does not designate the 
visitor register which includes the communication terminal information. 
In case of (a), the visitor register reads the communication terminal 
information from the gate location register 21 at the occurrence of a call 
connection to the communication terminal 60, and stores it. 
In case of (b), the correction is carried out using the first timer 
information. The first timer information is reset by the occurrence of a 
call connection to the communication terminal 60. If the visitor register 
receives the location registration signal from the communication terminal 
60 in such a state that no call connection has occurred to the 
communication terminal 60 before its first timer information has expired, 
the visitor register registers its number in the gate location register 
21. This is because the visitor register decides that the gate location 
register 21 is in the state of (b), if there occurs no call connection to 
the communication terminal for more than the fixed time T.sub.1. 
Thus, the inconsistency of information between the visitor register and the 
gate location register can be corrected. 
(4) According to the present invention, the information about a 
communication terminal which is absent in a visiting area can be 
automatically deregistered. The second timer information is used for this 
purpose. More specifically, the visitor register decides that the 
communication terminal 60 is not present in the visiting area when there 
is no communication for more than the fixed time T.sub.2 therebetween, and 
automatically deregisters the information about the communication terminal 
60.