text: 1. Field of the Invention
  The present invention relates to a communication system capable of performing voice communications and data communications using communication terminals such as personal computers with a built-in telephone function and personal computers that can be connected to telephone sets (hereinafter referred to as a "fixed terminal") and mobile telephone terminals with an information processing capability (hereinafter referred to as a "mobile terminal")
  2. Description of the Related Art
  One of the conventional mobility management processes is a location updating process for mobile communications. Known location updating processes are those disclosed in Japanese laid-open patent publications Nos. 264653/95, 162942/95, 129488/95, 209489/94, 283898/91, and 095037/90, and a GSM (Global System for Mobile communications) process, a PDC (Personal Digital Cellular) process, and an IS-95 process. These location updating processes will be described below. FIG. 1 of the accompanying drawings shows a communication system in which a location updating process is carried out.
  Mobile communication systems employ location registration areas provided for each operator or each predetermined geographical range. When the mobile terminal of a subscriber is switched on for the first time in a location registration area or moves from a location registration area into another location registration area, the mobile terminal sends a location registration change request to a database which is composed of location registers including a home location register (HLR) and a visitor location register (VLR). The database stores location registration information associated with mobile terminal numbers. When there is an incoming call for a mobile terminal, the database searches the location registration areas for the mobile terminal, and calls the mobile terminal in the location registration area which is determined. If a roaming service is available between different operators, then even when a mobile terminal roams into a service area of an operator to which the mobile terminal does not subscribe, the location registration information in the HLR of the home operator and the location registration information in the VLR of the operator which provides the roaming service can be updated by a location registration change request from the mobile terminal. While the mobile terminal is roaming, the mobile terminal is temporally allotted a roaming number for its own identification, and managed by the database. Therefore, no matter which service area a mobile terminal may be located in, its location registration information is updated, allowing connecting incoming calls to the mobile terminal.
  In FIG. 1, a mobile terminal 505 subscribes to an operator which covers a service area 510, and information of the mobile terminal 505 is managed in a database (HLR) 500. When the mobile terminal 505 moves from a location registration area 511 into a location registration area 512, the mobile terminal 505 sends a location registration change request to a database (VLR) 504 via a mobile switching office 502. The database (VLR) 504 sets up location registration information and allots a roaming number, and notifies the database (HLR) 500. In response to the notification from the database (VLR) 504, the database (HLR) 500 updates the location registration information of the mobile terminal 505 and sets up the roaming number thereof. When an incoming call for the mobile terminal 505 arrives at a mobile switching office 501, the mobile switching office 501 sends a location information inquiry to the database (HLR) 500. The mobile switching office 501 confirms that the mobile terminal 505 is located in a location registration area 512 covered by the mobile switching office 502, acquires the roaming number for the incoming call, and connects the incoming call to the mobile switching office 502. In response to the incoming call from the mobile switching office 501, the mobile switching office 502 sends an inquiry about the mobile terminal 505 to the database (VLR) 504, using the roaming number, and acquires a location registration area in which the mobile terminal 505 is located and a mobile terminal number (which may be a temporary number for concealing its real number). The mobile switching office 502 calls the mobile terminal 505 in an area to be called (which is usually the same as the location registration area). If someone answers with the mobile terminal 505, the mobile switching office 502 connects an incoming call circuit from the mobile switching office 501 and the communication path of the mobile terminal 505, for communications to start between the calling and called parties. When an outgoing call is made from a mobile terminal, a location registration change request may automatically be sent from a mobile switching office to a location register.
  Japanese laid-open patent publication No. 264653/95 discloses a dual-mode system for a cordless terminal and a mobile terminal. When switched to a slave unit of the cordless terminal, the wired telephone number of a master unit of the cordless terminal is registered as a call forwarding destination in a location register of a mobile communication system. When there is an incoming call for the mobile terminal, an incoming call is rerouted to the master unit of the cordless terminal.
  According to Japanese laid-open patent publication No. 162942/95, where there are a plurality of mobile switching offices for routing control in one location registration area, a routing number for a terminal in a location register is updated when a call is disconnected, so that the routing number can be updated into an optimum routing number in the same location registration area.
  Japanese laid-open patent publication No. 129488/95 reveals location updating between private networks for private mobile communications.
  In the disclosure of Japanese laid-open patent publication No. 209489/94, when terminals concentrate in the area covered by a certain control station, control is divided between a management station which manages positional information in an entire service area and the control station for thereby preventing congestion.
  Japanese laid-open patent publication No. 283898/91 shows a system having a plurality of home location registers. If there are many communications performed in a visitor area outside a home area, then a terminal is controlled as if it were located within the home area, using a home memory in the visitor area, so that access to a home location register of its own is reduced to prevent congestion.
  According to Japanese laid-open patent publication No. 095037/90, location registration information is locally shielded in radio base stations, and when there is an incoming call, the incoming call information is transferred to all the base stations, which determine whether a call is to be made or not based on the incoming call information.
  GSM allows location registrations to be canceled and started. Either version of GSM is a mobility management system using location updating as described above with reference to FIG. 1.
  One conventional mobility management process is a location tracking process for personal communications. This mobility management process is disclosed in Japanese laid-open patent publication No. 308674/93 and an article entitled "An intelligent location tracking method for personal terminal FPLMTS/UMTS communications". The location tracking process will be described below with reference to FIG. 2 of the accompanying drawings. In personal communications, each individual has a number, and performs a tracking process. A plurality of items of information as to which terminal is used to communicate in each of months, days, weeks, and times are registered as action schedules of individuals. When there is an incoming call, a terminal is called on the basis of the registered information. Tracking information is managed by a home database, and includes individual's numbers and individual's authentication numbers as individual's information and a plurality of incoming call terminal numbers as action schedules.
  In FIG. 2, a database 604 belongs to an switching network 600 of an individual ABC. It is assumed that the database 604 manages, as part of subscriber's information, an individual's number "123", an individual's authentication number "556677", a first candidate terminal number "306111" as the number of a fixed terminal 606 scheduled to communicate in a certain day at a certain time, and a second candidate terminal number "307111" as the number of a fixed terminal 607, as shown in Table 1 below.
  TABLE 1 ______________________________________ Individual's name ABC Individual's number 123 Individual's authentication number 556677 1st candidate terminal Fixed terminal 606 1st candidate terminal number 306111 2nd candidate terminal Fixed terminal 607 2nd candidate terminal number 307111 ______________________________________
  When there is an incoming call for the subscriber ABC at this time from a transmitting switching network 601, the incoming call is sent to the switching network 600. The switching network 600 searches the home database 604 for a present incoming call destination, using the individual's number "123" of the subscriber ABC as a parameter, and attempts to make a call with the first candidate terminal number "306111", obtained from the database 604, which is the number of the fixed terminal 606. It is assumed that an switching network 602 is a first incoming call destination network to which the fixed terminal 606 belongs. If the fixed terminal 606 is busy or no one answers at the fixed terminal 606, then the switching network 600 obtains the second candidate terminal number "307111", which is the number of the fixed terminal 607, from the database 604, and attempts to make a call with the second candidate terminal number "307111". It is assumed that an switching network 603 is a second incoming call destination network to which the fixed terminal 607 belongs. If the fixed terminal 607 answers, then the switching network 600 sets up a connection between the switching networks 601 and 603, allowing the calling and called parties to communicate with each other.
  The article entitled "An intelligent location tracking method for personal terminal FPLMTS/UMTS communications" describes that after location updating of a subscriber has been studied for a certain period of time, location tracking pattern information of highest probability is generated.
  The conventional location updating processes have suffered various problems.
  The first problem is that the conventional location updating processes require a large amount of communications between exchanges and a home database, typically a home location register, which stores information (such as location registration information) of communication terminals, resulting in a reduction in the processing capability. Reasons for the first problem are that the present location updating processes are applicable to mobile communication networks only, and for communicating with a certain mobile communication terminal, an exchange necessarily accesses the home database and calls the mobile communication terminal based on location registration information thereof which is obtained from the home database.
  The second problem is that there are instances in which a mobile communication terminal may not be called and ineffective calling may be made even if the mobile communication terminal is located in a location registration area which has last been updated. The second problem arises because the mobile communication terminal may sometimes be located in a building and cannot be accessed by radio waves. Since the mobile communication terminal does not reply when it is called in such an occasion, the calling party hears an announcement of absence from the network, and may find it necessary to call another mobile communication terminal which the calling party can expect to communicate with.
  According to the third problem, a mobile communication terminal cannot be called and ineffective calling is made if the mobile communication terminal is not present in a network which is subject to location updating and is present in a network which is not subject to location updating. The third problem occurs because the present location updating processes are applicable to mobile communication networks only, but not fixed wired networks. Even if a fixed communication terminal is present in a location where no mobile communication network services are available, since a calling subscriber makes a call to an updated area where the mobile communication terminal has been last present and the mobile communication terminal does not reply as it is not in the updated area, the calling subscriber cannot communicate with the mobile communication terminal unless he obtains the number of the fixed communication terminal and calls the fixed communication terminal.
  The fourth problem is that the ineffective calling due to the second and third problems may be avoided by a detaching process in which a home location register is notified of an absence when a mobile communication terminal enters an area not accessible by radio waves or is switched off, but the detaching process results in increased signal traffic between mobile communication terminals and the network, causing congestion. This is because a mobile communication terminal may enter an area of weak field intensity, but may not necessarily stay in such an area not accessible by radio waves. The mobile communication terminal initiates the detaching process when it enters an area where the field intensity is lower than a certain preset level and initiates an attaching process when the field intensity becomes higher than the preset level. Consequently, the mobile communication terminal tends to repeat the detaching and attaching processes alternately when it is moves between a radio zone where the field intensity is unstable and a boundary region of such a radio zone.
  The fifth problem is that the present location updating processes are liable to incur a lot of expenses for communications. Specifically, inasmuch as the present location updating processes are applicable to mobile communication networks only, but no fixed wired networks, an incoming call arrives at a mobile communication terminal via a mobile communication network though a fixed communication terminal is readily available. To prevent such a condition, it is necessary for a subscriber to tell people who are likely to make a call, the number of the fixed communication terminal most readily available to the subscriber. However, such a solution results in an increased expenditure of time and money for communications.
  The sixth problem is that the conventional location tracking process is apt to cause many wasteful incoming calls. Specifically, while a subscriber is in motion, it is not possible to set up accurate information to be tracked, and due to a change in schedule, tracking information including a tracking sequence is not in conformity with a location where the subscriber is present, with the results that no one may response to an incoming call or the subscriber may not be present even if an incoming call is answered. In some cases, the subscriber may be present at the final incoming call destination on the tracking list, and an incoming call may not reach the subscriber.