Method of completing telephone call in telephone system

Method for automatically calling back when called user is busy in telecommunication system

The invention relates to a method for completing a call when a calling user calls a called user but the called user does not answer. The user is part of a telecommunication system, which includes at least one cellular mobile communication network. One of the users is connected via a mobile telecommunication network, while the other user is connected via a mobile telecommunication network or via a public switched telephone network. The called user is permanently registered in a home location register and temporarily registered in a visitor address register, which is known by the home location register and is used in the mobile network .

Nowadays, mobile telephony is a rapidly developing technology. Many mobile telecommunications systems (European GSM system is one of them) have passed the initial basic development stage. The designers of these systems are currently working on further improvements to these systems and other related system improvements and the introduction of optional services. Affairs. Land-wide public switched telephone networks have long included services that can be accepted, such as "automatic callback when the called user is busy with another call" or "automatic callback when the called user does not answer." This known technique is based on a database in which the identification code of the relevant user is established, and the database is connected to a telephone exchange that manages the calling user and/or the called user. The problem with porting this technology to a mobile telecommunication system is that the user is mobile in the system. Because in the telecommunication network or system, the mobile user address location is often mobile. Therefore, when it is possible to establish a call connection, especially when a considerable amount of time has elapsed between the initialization of the "automatic callback service" and the execution of this service, many difficulties will be encountered in determining the location of the user. Services of this nature can also be found in some mobile telecommunication systems. For example, the automatic call-back service technology known in the art can be learned from Japanese Patent Specification JP3-190,494. According to the known method, the identification codes of both the calling user and the called user are stored in a storage unit and wait for the called to receive the call. When the called party is found, a call connection is established with the aid of the data retrieved from the storage unit. The disadvantage of this technique described in the earlier patent specification is that when initially trying to call the called user, the storage address is only used to move out of the cell area where the user is located. When the mobile user moves the cell area, it is no longer possible to locate the mobile user. Therefore, this technique is only suitable for smaller networks. Japanese Patent Specification JP-3-235,563 also discloses an automatic callback method in which user data is stored in a called mobile unit. Although this method solves the problem of finding mobile users, it needs to provide additional equipment to enable the service in each mobile unit.

The purpose of the present invention is to provide automatic callback in a cellular mobile telecommunication network, even if the calling user and/or the called user have moved a considerable distance in the network from the moment the callback service is initialized to the moment the service is executed. Under the circumstances, the business can also be completed. According to the present invention, the above-mentioned problem is solved by storing the location identifiers of these two users in an existing central database in the mobile telecommunication network. The central database, the so-called initial address register HLR, has the traditional purpose of keeping a record of the location of all mobile units registered in the system in the network and their location at that moment. The above purpose can be made possible by connecting the initial address register HLR with the local data in the system, the so-called visitor address register VLR. The VLR stores a service area code, which reveals exactly what the mobile unit has at each moment. Location. According to the present invention, the ability of the initial address register to know in which access address register all mobile units are registered is used to locate the aforementioned user before calling back. This makes it possible to establish a call even if the user has moved from a first access address register to a second access address register during the time interval between the initial call back and the execution of the call back. In this regard, the relevant mobile users do not need additional equipment, which is different from the earlier known technologies, which require additional equipment. The present invention will be described in more detail with reference to the preferred embodiments of the present invention and the accompanying drawings. The features of the invention are stated in the following claims.

Figure 1 is a block diagram illustrating the business situation between a calling user in a land-based public telephone switching network and a called user in a GSM-type cellular mobile telecommunication network.

Fig. 1a is a flow chart showing a method of the present invention, in which the structure shown in Fig. 1 is used.

Figure 2 is a schematic diagram showing the business situation between a calling user in a GSM-type mobile telecommunication network and a called user in a land-wide public telephone switching network.

Fig. 2a is a flowchart illustrating a method of the present invention, in which the structure shown in Fig. 2 is used.

Fig. 3 is a schematic block diagram illustrating the business situation between a calling user and a called user in a GSM-type mobile communication network.

Fig. 3a is a flow chart illustrating a method of the present invention, in which the structure shown in Fig. 3 is used.

The GSM-type public land mobile network (PLMN) includes a gateway mobile phone service switching center, which is connected to several local mobile service switching centers, and each local mobile service switching center is connected to multiple base station controllers in turn. The GSM network is specified in the so-called GSM recommendation, and the structure of this network is specifically described in the GSM03.02 recommendation. Each base station controller is connected to multiple base stations. Each base station monitors a geographic area, which is called a cell. The PLMN network also includes a central database, a so-called initial address register, which is connected to the gateway or the central mobile phone service switching center, and is also connected to all local mobile phone switching centers in the PLMN network. Those mobile units that have subscribed to the mobile telecommunications network are registered in the initial address register. Each local mobile telephone switching center includes a local database called a visitor address register, and all mobile units located in one of the cells managed by the local mobile telephone service switching center at any given moment are registered in the visitor address register .

Figure 1 shows only one of the local mobile services switching center MSC, the base station controller BSC, the visitor address register VLR and the base station BS, which are all necessary for implementing the present invention. For the sake of clarity, the repeated above units have been deleted from the figure. A mobile unit B1 belonging to the public land mobile network PLMN and located in a cell area controlled by the visitor address register VLR at this time is simultaneously temporarily registered in the visitor address register VLR and permanently registered in the aforementioned initial address register HLR. The initial address register HLR is always informed of the visitor address register VLR registered by the mobile unit B1 at that moment. Figure 1 also shows a portion of the land-wide public telephone switching network required by the present invention. The public telephone switching network includes a local exchange LE connected to the gateway mobile switching center in the PLMN network. This unit-one connection of the two networks means that all signaling between the public switched telephone network PSTN and the PLMN network must pass through the gateway mobile telephone service switching center GMSC. The calling user A1, the so-called A user is permanently connected to the local exchange LE, and the aforementioned mobile unit B1, which is the called user, the so-called B user communicates with the base station BS via a wireless link. The wireless link is shown in the figure with a thick dashed line. The aforementioned permanent connections between the nodes GMSC, HLR, MSC, BSC, BS, LE, and A1 are shown in bold solid lines in the figure. The signaling (described in more detail below) is of course carried over the permanent link, although the signaling has been drawn on one side of the above-mentioned link for clarity. The signaling in the figure is drawn with thin solid lines. The arrow on the signaling line indicates the direction of signaling. The signaling between the local exchange LE and the initial address register HLR is sent to the gateway MSC, which is shown by a thin solid line including two-way arrows in FIG. 1, and is the same for this signaling. The purpose of temporarily reducing the signal is to make the description of Figure 1 easier to understand. The signaling shown in FIG. 1 and necessary for implementing the present invention does not represent all the signaling protocols performed to establish a call. Figure 1 only shows the signaling in the two networks PSTN and PLMN, while the text discloses the signaling between two related users A1 and B1. Also not shown in Fig. 1 is the signaling that is considered to belong to the well-known technology.

The above-mentioned mobile telecommunications system PLMN works in accordance with GSM recommendations. However, it is understood that the described invention can also be used in similar systems. The exemplary embodiment described in detail below includes an "automatic callback when busy" service. As mentioned earlier, in the case of automatic callback, it is important to be able to determine the location of the called mobile user B1, even if the mobile user has moved a long distance geographically and has entered the control of another access register When the area of a mesh. The method of the present invention proposed below can perform this basic function and includes the following protocol steps:-User A1 calls user B1 and tries to establish a call connection.

-A user A1 learns that B user B1 is busy with another call through a busy or busy tone, that is, a series of fast short room signals. These two steps are well known in the art and form part of the traditional signaling technology, so they will not be discussed in detail here. The method of the present invention includes the following further steps:-User A1 dials the number "5" on his telephone keypad, thereby requesting an "automatic callback when busy" service.

-The service request is transferred to the local exchange LE.

-A "call completed" message 1 is sent from the local exchange LE via the gateway mobile services switching center GMSC to the initial address register HLR.

-The arrival of message 1 at the initial address register results in the generation of a reference number Crefi, which is placed at the end of a queue 10 in the initial address register HLR. The queue includes reference numbers assigned to different users who have attempted to establish a call to the B user. If there is no earlier attempt to establish a connection to B user B1, queue 10 is established and the reference number of the "call completed" message 1 is placed at the top of the queue.

-The initial address register HLR knows which visitor address register the B user B1 is registered in at that moment, and it transfers the "call completed" message 1 to the visitor address register VLR.

-The visitor address register VLR registers the "call completed" message 1 and sends a confirmation message 2 "call completed confirmed" to the initial address register HLR.

-The initial address register sends the confirmation message 2 together with the reference number Crefi to the local exchange LE via the central mobile switching center.

-A user A1 is informed of the confirmation message 2 by the termination of the busy tone, after which, the A user releases its connection with the local exchange LE by putting down his phone handset.

-When the current call with another user ends, the B user B1 is idle to receive the call.

-The local mobile phone service switching center of B subscriber B1 notifies the visitor address register VLR subscriber B1 of the new state. This signaling is not shown in Figure 1.

-A "B idle" message 3 is sent from the visitor address register VLR to the initial address register HLR.

-The initial address register HLR confirms the "B idle" message 3 to the visitor address register VLR by sending a confirmation message 4 "B idle is confirmed".

-The reference number Crefi (it is considered to be at the head of the queue 10 at this time) is sent from the initial address register HLR together with the "B idle" message 3 via the gateway mobile services switching center GMSC to the local exchange LE.

-A user A1 learns that B user B1 is idle and waiting to receive a call through a series of fast short ringing signals, so user A confirms the message by picking up his phone handset, and then the local exchange LE learns the new state of user A, namely A The user has answered. This kind of signaling between the A user A1 and the local exchange LE is a well-known technique, and therefore is not shown in FIG. 1.

-A starting address message IAM1 including the telephone number of the B subscriber B1 together with the reference number Crefi is sent from the local exchange LE to the gateway mobile switching center GMSC.

The following three procedural steps belong to the general signaling protocol in GSM mobile phones, so they are not described in Figure 1. The purpose of these three protocol steps is to find a mobile station roaming number MSRN1, which is temporarily allocated to B user B1 when the connection is established. Later, this roaming number becomes the initial address message sent to the local mobile services switching center MSC that the B user happens to use at that moment.

-An inquiry about the roaming number assigned to the B subscriber B1 is sent from the gateway mobile services switching center GMSC to the initial address register HLR.

-The initial address register HLR (which contains the information revealing the visitor address register where the B user B1 is at that moment) transfers the reference/inquiry to the visitor address register VLR.

-The visitor address register VLR sends the information related to the roaming number of the B subscriber B1 to the gateway mobile services switching center GMSC via the initial address register HLR.

The following protocol steps are shown in the figure:-Establish a connection from the A user A1 to the B user B1 by sending the initial address message IAM1 and the mobile station roaming number MSRN1 from the gateway mobile switching center GMSC to the local mobile services switching center MSC. According to the present invention, the reference number Crefi is sent along with the initial address message IAM1 and the roaming number MSRN1. The reference number is then transferred to the visitor address register VLR.

-Through a common signal B user B1 learns of the call of A user A1, then B user answers the call by picking up his phone or some corresponding action, and the connection is considered to be established.

-The local mobile services switching center MSC of the B subscriber B1 informs the visitor address register VLR of the new status of the B subscriber B1, that is, the B subscriber has responded. This signaling is not shown in Figure 1.

-The visitor address register VLR sends a "B has been answered" message 5 together with the reference number Crefi to the initial address register HLR.

-The initial address register removes the reference number Crefi from the queue 10. As an additional protective measure, when the above method is performed, it is possible according to the present invention to allow the reference number Crefi to be sent along with the inquiry related to the mobile service roaming number MSRN1 of the B user. In this case, the reference number is transferred from the gateway mobile switching center GMSC to the local mobile switching center along two different routes. In this regard, the reference number Crefi is directly transmitted from the gateway mobile switching center GMSC to the local mobile switching center according to the above-mentioned method, and is also transmitted via the initial address register HLR. In this way, when a call is connected, if the reference number is lost for some reason, for example, due to a collision with a call from another user, the redundant transmission can ensure the transmission of the reference number Crefi.

It should also be noted that when a mobile unit switches from one access address register to another, the signaling is implemented in a way that is traditionally associated with so-called roaming in a mobile telecommunication system or network. The protocol used to determine the location of the mobile unit is specified in the GSM recommendation 03.12. The automatic callback protocol of the present invention is not affected by this "roaming", and the reference number Crefi is always stored in the initial address register HLR, which is notified of the change in the visit address register.

Figure 1a is a flow chart describing the above protocol. The simplified description of this flowchart and the following subsequent statutes can be used to read together with Figure 1 and the corresponding description. Refer to Figure 1 for the abbreviations and abbreviations in the text of this flowchart. These abbreviations and abbreviations have been described in the above examples. The method of the protocol refers to the flowchart since the A user A1 has called the B user B1 and requested the "automatic callback when busy" service after receiving the busy tone. The method then continues according to the following description and according to figure 1a:-According to block 100, the "call completed" message is sent from the local exchange LE to the initial address register HLR.

-According to block 101, the reference number Crefi is generated and placed at the end of the queue in the initial address register HLR.

-According to block 102, the initial address register HLR sends a "call completed" message to the visitor address register VLR.

-According to block 103, the VLR sends a confirmation message "Completed call confirmed" to the initial address register HLR.

-According to block 104, the initial address register HLR sends a confirmation message "call completion confirmed" and the reference number Crefi to the local exchange LE.

-According to block 105, the B subscriber B1 becomes available, by terminating a current call. The local mobile services switching center MSC of the B subscriber B1 informs the visitor address register of the new status of the B subscriber.

-According to block 106, the "B idle" message is sent from the visitor address register VLR to the initial address register HLR. Then the initial address register HLR confirms the message to the visitor address register VLR.

-According to block 107, the reference number Crefi and the "B free" message are sent from the HLR to the local exchange LE.

-According to block 108, A user A1 learns that B user B1 is free to receive his call, then A user A1 picks up his phone handset.

-According to block 109, the start address message IAM1 and the reference number Crefi are sent from the local exchange LE to the local mobile services switching center MSC.

-According to block 110, the reference number Crefi is sent from the local mobile switching center MSC to the visitor address register VLR.

-According to block 111, the call is connected by means of the start address message IAM1 and the B subscriber B1 answers.

-According to block 112, the visitor address register VLR sends the reference number Crefi and the message "B has been answered" to the initial address register HLR.

-According to block 113, the initial address register HLR removes Crefi from the queue.

Another method of the present invention will now be discussed. Generally speaking, the same GSM-type public land mobile network PLMN as described above is used in this method. The exemplary embodiment described in detail below relates to the "automatic callback when the called user does not answer" service. In this case, the calling user is a mobile unit belonging to the public land mobile network PLMN, and the called user is a unit permanently connected to the public network.

Similar to FIG. 1 FIG. 2 only shows the local mobile service switching center MSC, the base station controller BSC, the visitor address register VLR, and the base station BS necessary to implement the present invention. A mobile unit A2 belonging to the PLMN network and temporarily located in a cell area controlled by a visitor address register VLR has already been described with reference to Figure 1. It is temporarily registered in the visitor address register VLR and permanently registered in the initial In the address register HLR. As mentioned earlier, the initial address register always knows exactly in which visitor address register the mobile unit A2 is registered at any given moment. Figure 2 also shows those parts of the PSTN network necessary to implement the invention, namely the local exchange LE. In this example, the mobile unit A2 is the calling user, the so-called A user, and communicates with the base station BS via a wireless link. The called user B2, the so-called user B, is permanently connected to the local exchange LE. The description of the details of the drawings made with reference to FIG. 1 can be directly applied to FIG. 2. The signaling shown in Figure 2 and necessary for the present invention does not represent all the signaling performed when a call is connected. The figure only shows the signaling in the two networks PSTN and PLMN, and the signaling to and from the two involved users A2 and B2 are only given in text. The figure also does not show signaling belonging to the well-known technology.

In the implementation of the automatic call-back service, when the calling user has moved a long distance geographically and has entered a cell area controlled by a register different from the register that registered the access address of the A user when the initial call was made At this time, it is important to determine the location of the mobile user. In this case, to determine the location of the calling user A2. The method of the present invention proposed below can accomplish this basic function and includes the following protocol steps:-A user A2 tries to establish a call connection with B user B2.

-A user A2 learns that B user B2 "didn't answer the call" through a ringing control tone that did not follow the answer. These two steps are well-known in the technical field, and the involved signaling protocols belong to traditional technologies, so they will not be described in detail. The method of the present invention further includes the following steps:-A user A2 dials the number "2" on his telephone keypad to request the service of "automatically call back when the called user does not answer".

-By normally sending signalling via the base station BS, the base station controller BSC and the local mobile telephone switching center MSC, this request is sent to the visitor address register VLR. This signaling is not shown in Figure 2.

-A "call completed" message 21 is sent from the visitor address register VLR to the initial address register HLR.

-The initial address register HLR sends the "call complete" message 21 to the local exchange LE through the GMSC center.

-The local exchange LE registers the "call completed" message 21, and sends a confirmation signal 22 "call completed confirmed" together with a reference number MRefi to the initial address register HLR via the GMSC center.

-The reference number MRefi is stored in a storage address 11 in the initial address register HLR. The storage address belongs to the A user A2 and contains reference numbers for establishing connections from the A user to different users.

-The initial address register HLR converts the confirmation 22 of "call completion confirmed" to the visitor address register VLR.

-The A user A2 learns the confirmation 22, after which the A user releases its connection to the PLMN network.

-B user B2 is activated, for example by B user picking up its phone handset or in some other way, to indicate that it is free to receive calls.

-B user B2 informs the local exchange LE of its new state through a traditional signaling protocol. This signaling is not shown in Figure 2.

-A "B idle" message 23 is sent from the local exchange LE to the initial address register HLR via the GMSC center.

-The initial address register HLR converts the "B idle" message 23 and the reference number MRefi to the local MSC via the visitor address register VLR.

-A user A2 learns that B user B2 is idle to receive a call, for example, through a series of fast short ringing signals. User A confirms this information, for example, by picking up his phone handset, and then the local MSC learns the new state of user A, that is, user A has confirmed that the call can be connected. The signaling implemented between the A user A2 and the local MSC is a well-known technology, so it is not shown in the figure.

-Connect the call according to known protocols. By sending an initial address message IAM2 together with the telephone number of the B user and the reference number MRefi from the local MSC to the local exchange LE via the GMSC center.

-B user B2 learns the call from A user A2 through a traditional ringing signal, and B user answers the call by picking up his phone. The call is then considered to be connected.

-B user B2 uses a traditional signaling protocol to notify the local exchange LE of his new state, that is, user B has answered. This signaling protocol is not shown in Figure 2.

-The local exchange LE sends a "B Answered" message 24 along with the reference number Mrefi to the initial address register HLR through the GMSC center.

-The initial address register HLR removes the reference number MRefi from its storage address 11.

Figure 2a is a flowchart illustrating the above method. The flowchart and the following simplified description of the method can be read together with Figure 2 and related descriptions. The abbreviations and abbreviations in the text part of this flowchart have been described in the above examples with reference to Figure 2. With reference to the method shown in the flowchart, user A2 has called user B2 and requested the service "automatically call back when the called user is busy with another call" after receiving the busy tone. The method proceeds according to the following description and according to Fig. 2a-according to block 200, the "call completed" message is sent from the visitor address register VLR to the initial address register HLR.

-According to block 201, the initial address register HLR switches the "call completed" message to the local exchange LE.

-According to block 202, the local exchange LE sends a confirmation message "call completion confirmed" and the reference number MRefi to the initial address register HLR.

-According to block 203, the reference number is stored in a storage address 11 in the initial address register HLR.

-According to block 204, the initial address register HLR converts the confirmation message 22 of "call completion confirmed" to the visitor register VLR, after which the subscriber A is notified.

-According to block 205, the B user B2 is activated and available for call connection. Then the B user B2 informs the local exchange LE of his new status.

-According to block 206, the "B idle" message is sent from the local exchange LE to the initial address register HLR.

-According to block 207, the initial address register HLR converts the "B idle" message together with the reference number MRefi to the local MSC.

-According to block 208, user A A2 learns that user B B2 is free to receive the call, user A confirms this message by picking up his phone handset or through some corresponding mobile phone procedure. Then the local MSC learns the new status of user A, that is, user A has confirmed that the call can be connected.

-According to block 209, the initial address message IAM2 is sent from the local MSC to the local exchange LE along with the reference number.

-According to block 210, B user B2 learns of the call from A user A2, then B user answers the call by picking up his phone handset, and the call is considered established by Bibo. Thus, the B user B2 informs the local exchange LE of his new status.

-According to block 211, the local exchange LE sends a "B has been answered" message and the reference number to the initial address register HLR.

-According to block 212, the initial address register HLR removes the reference number MRefi from the storage address.

The above exemplary embodiment of the "automatically call back when the called user does not answer the call" service has been made with reference to the situation when the calling user is a mobile unit and the called user is permanently connected to a land-wide public telephone switching network. description. However, it can be understood that this kind of service according to the present invention can be performed when either one or both of the users involved are a mobile unit or both are mobile units. It also applies to the previously described embodiment involving "automatic callback when the called user is busy on another call".

Another method of the present invention will now be discussed. This method utilizes the same GSM-type PLMN network as generally described above. The exemplary embodiment described in more detail below relates to a service "automatically call back when the called user is busy with another call". In this case, both the calling user and the called user are mobile units belonging to the PLMN network.

Like the previous figures, Figure 3 shows only those elements of the PLMN network necessary to implement the present invention. The PLMN network includes an initial address register HLR, the function of which has been described in the previous embodiment. In the embodiment of FIG. 3, the initial address register HLR is connected to two mobile services switching centers, here referred to as the first and second local mobile services switching centers MSCA and MSCB. For the sake of clarity. Other switching centers connected to the initial address register HLR have been deleted from the figure. Each of the two mobile switching centers is connected to a respective base station control unit, which are called first and second base station control units BSCA and BSCB, respectively. Each base station control unit is connected to a corresponding base station, called the first and second base stations BSA and BSB. Each MSCA and MSCB center includes a respective access address register, which is referred to herein as the first and second access address registers VLRA and VLRB, respectively. Similar to the description with reference to the previous embodiments, a first mobile unit A3 belonging to the PLMN network and temporarily located in a cell area controlled by the first visitor address register VLRA is temporarily registered in the visitor address register VLRA and permanently registered In the initial address register HLR. These also apply to a second mobile unit B3 located in another cell area and controlled by the second access address register VLRB. In the illustrated embodiment, the first mobile unit A3 is the calling user, the so-called A user, and the second mobile unit B3 is the called user, the so-called B user. As mentioned earlier, the initial address register always knows which visit address register VLRA or VLRB exactly the mobile units A3 and B3 are registered in at any moment. The communication between the mobile unit and the PLMN network runs in the same way as described above. The techniques detailed in the previous figures also apply to figure 3. The signaling shown in FIG. 3 and necessary for the present invention does not represent all signaling protocols that are executed when a call connection is established. The figure only shows the signaling performed in the PLMN network, and the signaling to and from the two related users A3 and B3 is only disclosed in text. The figure also does not show signaling that belongs to the well-known technology.

When performing an automatic callback service, it is important to be able to determine the location of the relevant mobile user, in this case the location of the calling user A3 and the called B user B3. This also applies to those cases when one or both of the users have moved a long distance geographically and have entered a cell area controlled by a visitor address register VLR that is different from that of the user registered at the time of the initial call. The method of the present invention proposed below can perform these basic functions and includes the following protocol steps:-A user A3 calls B user B3 to establish a call connection.

-A user A3 learns that B user B3 is busy with a call from another user through a busy tone, that is, a series of fast short tone signals. The above two steps are well-known in the art, and the signaling protocol forms a part of the traditional technology, and therefore will not be described in detail. The method of the present invention further includes the following steps:-A user A3 dials the number "5" on his telephone keypad, thereby requesting the "automatically call back when the called user is busy with another call" service.

-A user A3 informs the first visitor address register VLRA of its new state by signaling via the first base station BSA, the first base station control unit VSCA and the first local MSCA center. This signaling is of traditional type, and therefore is not shown in FIG. 3.

-A "call completed" message 31 is sent from the first access address register VLRA to the initial address register HLR.

-When the message 31 reaches the initial address register HLR, a reference number CRefj is generated, which is placed at the end of a queue 12 in the initial address register. The queue contains reference numbers that identify the different users who have tried to call the B user. If there is no earlier attempt to establish a connection to user B3, queue 12 is established, and the reference number Crefj of the "call complete" message 31 is placed at the top of the queue.

-The initial address register HLR knows which visit address register B user B3 is registered in at a specific time, and converts the "call completed" message 31 to the second visit address register, and the "complete call" message 31 to the second visit address Register VLRB.

-The second visitor address register VLRB registers the "call completed" message and sends a confirmation message 32 of "call completed confirmed" to the initial address register HLR.

-The initial address register HLR converts the confirmation message 32 of "completed call confirmed" to the first visit address register VLRA.

-User A A3 learns the confirmation message 32, after which user A releases his connection to the PLMN network.

-When ending the current call with another user, the B user B3 becomes available to receive the call.

-The local mobile services switching center MSCB of the B user B3 informs the second visitor address register VLRB of the new state of the user B3. This signaling is considered to be well-known and therefore not shown in FIG. 3.

-A "B idle" message 33 is sent from the second access address register VLRB to the initial address register HLR of the sending stage.

-The initial address register HLR sends a "B idle confirmed" confirmation message 34 to the second visitor address register VLRB "B idle" confirmation message 33.

-The reference number CRefi (it is assumed to be at the top of queue 2) is sent from the initial address register HLR to the first visitor address register VLRA along with the "B free" message 33.

-A and user A3 learn that B user B3 is free to receive a call through a series of fast short ringing signals, and then, user A confirms the information. The first access address register VLRA learns the new state of user A, that is, user A has confirmed that the call will be connected. The signaling between the A user and the first access address register VLRA is a public technology, so it is not shown in the figure.

The following three protocol steps belong to the traditional signaling protocol in GSM mobile communication technology, so they are not shown in the figure. The purpose of these three protocol steps is to find a mobile station roaming number MSRN3, which can be temporarily allocated to B user B3 when a connection is established. Later, the roaming number generates an initial address message IAM3 that is sent to the local exchange used by B at that time. It has the phone number of user B3.

-A query related to the roaming number of B subscriber B3 is sent from the first local MSCA center to the initial address register HLR.

-The initial address register HLR, which contains information about the visitor address register of the registered B user B3, converts the reference/inquiry to the second visitor address register VLRB.

-The second visitor location register VLRB sends the information related to the roaming number of the B subscriber B3 to the first MSCA center via the initial address register HLR.

The following protocol steps are shown in the figure:-By sending an initial address message IAM3 and mobile station roaming number MSRN3 from the first local MSCA center to the second MSCB center, a connection from user A to user B3 is established. According to the present invention, the reference number CRefj is accompanied by the initial address message IAM3 and the roaming number MSRN3. This reference is then transferred to the second access address register VLRB.

-B user B3 learns of the call from A user A3 through traditional signaling, therefore, user B answers the call by picking up his phone or by executing some other corresponding mobile phone protocol, and the call is considered The connection has been established.

-The local mobile service switching center of B user B3 notifies the second visitor address register VLRB of the new state of the user, that is, user B has responded. This signaling is considered traditional and is not shown in Figure 3.

-The second visitor address register VLRB sends a "B has been answered" message 35 together with the reference number CRefj to the initial address register HLR.

-The initial address register HLR deletes the reference number CRefj from the queue 12.

As an additional protective measure, when implementing the method of the present invention, it is possible to allow the reference number CRefj to be sent along with the inquiry involving the roaming number MSRN3 of the B user. The reference number is then transferred from the first local mobile services switching center MSCA to the second local mobile services switching center MSCB along two different routes. In this regard, as described above, the reference number CRefj is directly transmitted from the first local MSCA center to the second local MSCB center, and is also transmitted through the initial address register HLR. In this way, even if the reference number is lost due to some reason or other at the time of connecting the call, for example, the reference number is lost as a result of a collision with a call from another user, this redundant transmission can ensure the reference number CRefj. Transmit.

Figure 3a is a flowchart illustrating the above method. The following simplified description of the process and method can be read together with Figure 3 and the corresponding description. The abbreviations and abbreviations in the text part of this flowchart have been explained together with the previous embodiment and the description with reference to FIG. 3. With reference to the method shown in the flowchart, user A3 has called user B3 and requested the service "automatically call back when the called user is busy with another call" after receiving the busy tone. The method then continues according to the following description and according to Fig. 3a:-According to block 300, the "call completed" message is sent from the first visit address register VLRA to the initial address register HLR.

-According to block 301, the reference number is generated and placed at the end of a queue in the initial address register.

-According to block 302, the initial address register HLR transmits the "call completed" message to the second visitor address register VLRB.

-According to block 303, the second visitor address register VLR sends a confirmation message "completed call confirmed" to the initial address register HLR.

-According to block 304, the initial address register HLR transmits the confirmation message "Call completed is confirmed" to the first visitor address register VLRA. User A A3 learns of this confirmation, and then user A releases the connection by putting back his phone or using some corresponding mobile phone procedures.

-According to block 305, user B3 becomes idle by ending the current call with another user to receive the call. The mobile services switching center MSCB of the B user B3 notifies the second visitor address register VLRB of the new status of the B user.

-According to block 306, a "B idle" message is sent from the second access address register VLRB to the initial address register HLR.

-According to block 307, the reference number CRefj is sent from the initial address register HLR to the first visitor address register VLRA together with the "B idle" message. A user A3 learns that B user B3 can be used to receive calls.

-According to block 308, user A picks up his phone handset or executes some corresponding mobile phone protocol. The first access address register VLRA learns the new state of the A user, that is, the A user has responded.

-According to block 309, by sending an initial address message IAM3 and a reference number from the first local mobile services switching center MSCA to the second mobile services switching center MSCB, a connection from the A user A3 to the B user B3 is established.

-According to block 310, the reference number is transferred from the MSCB to the second visitor address register VLRB.

-According to block 311, B user B3 learns of the call from A user A3, B user responds to the call by picking up his phone handset, or by executing some other corresponding telephony protocol, and the call is considered to be connected. The local service switching center of the B user B3 notifies the second visitor address register VLRB of the new state of the user, that is, the B user has responded.

-According to block 312, the second visitor address register VLRB sends a "B has been answered" message together with the reference number CRefj to the initial address register HLR.

-According to block 313, the initial address register HLR deletes the reference number CRefj from the queue.

In the above illustrative embodiment, the automatic call-back service appears in normal business situations. These three situations are: 1. The calling user A is permanently connected to the land-based telephone network, and the called user B is a mobile unit.

2. The calling user A is a mobile unit, and the called user B is permanently connected to the land-based telephone network.

3. Both the calling user A and the called user B are mobile units, and they are located in a cell controlled by different access address registers in a mobile telecommunication network.

In the above three business situations, some structural deformation is possible. For example, two mobile units can be located in a cell controlled by the same access address register. It will be easy to see that even in this case the present invention can determine the location of two users. It is also conceivable that the mobile units can be located in different mobile telecommunication networks, and the locations of these units can be determined by different initial address registers. This structure needs to pass through a public telephone switching network before establishing a call connection. According to the present invention, the above-mentioned situation is realized using a combination of the first and second embodiments. As will be understood, several other variations of the three embodiments are conceivable, and it is obvious to those skilled in the art that these embodiments do not limit the use of the present invention. It is also possible for some mobile telecommunication networks to include more than one initial address register. However, this modification does not limit the scope of the present invention, but it will only be seen as a modification of the above situation, where each mobile unit belongs to a different mobile telecommunication network, but has the difference that it does not need to pass through a public telephone exchange network. . As mentioned above, the present invention can be applied to all mobile communications, in which mobile units are centrally registered in the system, such as the American Digital System ADC. This also means that the term mobile unit used in this document can be interpreted differently, depending on whether the mobile telecommunication network controls vehicle users, pedestrian users, paging systems, data terminals, etc.