JP3250129B2 - Packet service uninterrupted handover method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for uninterrupted handover of packet service in mobile data communication realized by a packet network and a mobile station connected thereto.

[0002]

2. Description of the Related Art First, a packet switching system and a handover in mobile communication, which are the premise of the present invention, will be described. First, the packet switching system will be described using ISDN as an example. FIG. 6 is a diagram illustrating a packet network configuration of ISDN. The packet terminal 1 is accommodated in a packet switch 3 via an ISDN switch 2 which is a subscriber concentration stage. The packet switch 3 is connected via a packet relay network 4 to a packet switch 5 accommodating a communication partner terminal,
Further, communication with the terminal 7 via the ISDN exchange 6 is enabled. Between the terminal 7 and the packet switch 5,
A communication channel is controlled by an ISDN channel control procedure, and a protocol in which a packet network control procedure is added to X.25 of ITU-T recommendation is used.

FIG. 7 is a diagram showing a communication sequence example and a communication phase. In the packet communication conforming to X.25 of the above ITU-T recommendation, there are three phases of call setup, data transfer and call release. In the case of ISDN packets, in addition to these three phases, ISDN is used. There is a channel setup phase and an ISDN channel release phase. Regarding these, for example, "TTC Standard II" issued by Nippon Telegraph and Telephone Consultative Committee in February 1994,
Alternatively, it is possible to refer to the description of NTT Technical Reference Material “Interface Conditions for INS Net Service” issued in January 1993. Hereinafter, description will be given according to a sequence. If the packet terminal 1 accommodating the ISDN network
In order to perform packet communication, first, a channel for performing packet communication is set with the packet switch 3 through the ISDN switch 2 by the ISDN channel control protocol. After setting the communication channel, the packet terminal 1 transmits a CR packet to the packet switch 3, and the packet switch 3 having received the CR packet
The CN packet is transmitted to the destination packet switch 5 accommodating the partner terminal, and the destination packet switch 5 transmits the CN packet to the destination terminal.

[0004] When responding to call setup, the called terminal uses a CA.
The call setting is performed by transmitting the packet to the destination packet switch 5, transmitting the CC packet from the destination packet switch 5 to the originating packet switch 3, and transmitting the CC packet to the originating terminal 1. Is completed. When the call setup phase is completed, the process proceeds to the data transfer phase,
Transfer of DT packets between terminals becomes possible. In a circuit switching system typified by a general telephone, when a call is in a busy state, the switching system merely maintains a communication path, and the contents of the communication are transparent. Has a feature of performing error correction, retransmission control, sequence control, flow control, and the like. With this feature, the reliability of data transfer is improved. When releasing the connection, the terminal shifts to the call release phase by transmitting and receiving a call release packet between the terminals.

Next, handover will be described. This is described in, for example, "The Second Generation Cordless Telephone System Standards" issued by the Radio System Development Center in March 1993, or by the Nippon Telegraph and Telephone Consultative Committee in February 1994. Of "TTC Standard II" can be referred to. Handover refers to the function of switching channels while maintaining the communication state.
In many mobile communication networks, this function is provided so that communication can be continued even if a communicating terminal moves to another wireless area. Figure 8 shows the second generation cordless phone system
1 shows a (PHS) network configuration. The mobile mobile phone 1 has an R
Radio base station 2 with radio interface conforming to CR standard
And the radio base station 2 is connected to an ISDN exchange through an ISDN interface for mobile phones which is a TTC standard. After the ISDN exchange, the operation is the same as in a normal ISDN.

The function of the location register is controlled by the high-performance switching processing node 7.
Is connected to each ISDN exchange via a common line communication network conforming to the ITU-T Recommendation No. 7 signaling system. According to the handover function, for example, even when the portable mobile phone 1 during a call moves from the cell of the radio base station CS # 1 to the cell of the CS # 2, the call can be continued. FIG. 9 shows an example of a handover sequence. As can be seen from the figure, a handover in circuit-switched mobile communication involves setting up a line physically in a new wireless area and switching over from the original line, resulting in a short break in communication during switching. Although it is, it can be realized relatively easily.

[0007]

As described above, in the packet switching system, even in the data transfer phase, the call state is changing, and both the terminal side and the network side are conscious of this state and control. Also, the frame on which the packet is
The transmission and reception sequence numbers are assigned, and the terminal side and the network side constantly monitor the frame for any omission or abnormal order. Further, in the packet network, it is necessary to hold the data packet until a delivery confirmation is returned from the terminal. Therefore, a method in which a physical line is simply set to a new cell and switched, such as circuit switching, cannot be adopted because of protocol inconsistency. In the mobile communication based on the packet switching method, in order to realize the handover, it is necessary to take over the communication state before the movement until the communication is resumed after the movement. If the call state or the like is taken over, the procedure of the handover is inevitably complicated, and the time required for the processing becomes long. This can cause data loss or disconnection due to the no response timer. In order to avoid this, temporary regulation processing of communication is required.

[0008] In addition, only by setting a new communication link, a packet from a partner terminal does not correctly reach the mobile terminal through the link. As described above, a protocol in which a packet network control procedure is added to X.25 is used between packet switches, but it is necessary to change the routing information used here. Further, when the handover extends over a plurality of packet exchanges, it is necessary to take over information between the packet exchanges. When the handover extends over a plurality of operators, it is necessary to take over the information between the operators. The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems in the conventional technology and realize a handover without losing data during communication. It is an object of the present invention to provide an interrupted handover method.

[0009]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
A step of regulating communication during link switching by the packet switch; a step of taking over a packet waiting for a response to a buffer of the switched link and holding the packet, using a retransmission function of a packet protocol to prevent data loss, and a step of preventing packet loss. It has a step of setting and releasing a link by taking over information of a link or a communication state within a switch or between packet switches, and a step of exchanging information with a location register for other mobile communication-specific processing. This is achieved by a packet service uninterrupted handover method. More specifically, when both cells before and after the mobile data terminal moves are connected to the same packet switch, they are connected to different mobile communication base stations, and these mobile communication base stations use different packet exchanges. When connected to an exchange, each cell has its own additional steps, for example, when the cell moves across mobile communication networks of different operators.

[0010]

In the packet service uninterrupted handover method according to the present invention, under the above-mentioned various conditions, a step of restricting communication during link switching by the packet switch;
Handover of the packet waiting for response to the buffer of the link after switching and holding it, using the retransmission function of the packet protocol to prevent data loss, and information on the link and communication status within the packet switch or between packet switches. Taking over and setting and releasing links,
For other mobile communication-specific processing, the step of exchanging information with the location register makes it possible to implement handover without causing any packet protocol inconsistency and without losing packets even under a wide range of conditions.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a connection configuration for performing a handover based on a packet service uninterrupted handover method according to an embodiment of the present invention. In the configuration shown in the present embodiment, the packet terminal 5 and the mobile network 6
Subscriber-based packet switch that accommodates the network (indicated as "PS" in the figure)
2, a relay network 3 for relaying between stations, and a location register (“L” in FIG.
R) 4 and a plurality of mobile communication switching centers (“MS” in the figure) connected to the packet network 1.
C), a plurality of radio base stations (denoted as “BS” in the figure) 8 under the control of each mobile communication switching center 7, and a location register (“LR” in the figure) which performs database processing of mobile communication and the like. ) 9).

[0012] The relay network 3 operates in a manner other than packet switching.
For example, a cell relay or the like may be used. The location registers 4 and 9 do not exist as physical nodes and may be logically defined, or may be shared by a plurality of networks. The transmission network between the packet switches 2 and 7 and the location registers (LR) 4 and 9 or the location register is not limited to a common channel signaling network. Now, in the embodiment shown in FIG. 1, the mobile data terminal 10 uses the packet switch (PS) in the cell of the radio base station (BS) # 1n under the mobile communication switching center (MSC) # 1.
While moving while performing data communication with the fixed packet terminal accommodated in # 0, the mobile communication switching center (M
SC) Similar to # 1, the radio base station (B) under the mobile communication switching center (MSC) # 2 connected to the packet switch (PS) # 1.
S) It is assumed that it is necessary to switch the radio base station in the cell # 2m. FIG. 2 shows a communication sequence and an outline of processing of main nodes in this case.

In FIG. 2, a handover request signal output from the mobile data terminal 10 that has learned the necessity of handover due to a decrease in signal level or the like is transmitted to a destination radio base station.
(BS) # 2m, via the mobile switching center (MSC) # 2,
Delivered to Packet Switch (PS) # 1. Upon receiving the handover request signal, the packet switch (PS) # 1 immediately sends a non-receivable packet to the terminal (fixed packet terminal) of the communication partner. The partner terminal (fixed packet terminal) that has received the unreceivable packet stops transmitting the data packet. Next, the mobile data terminal 10 requests the location register (LR) 9 to perform a database update process or the like accompanying the handover. If there is no problem, a link with the destination radio base station (BS) # 2m is set.

At this time, the state at the time of communication by the radio base station (BS) # 1n is taken over as it is to prevent protocol inconsistency. Thereafter, a call setting acceptance signal is transmitted to the mobile data terminal 10 via the destination radio base station (BS) # 2m. Once the new link has been established, the fact that the packet transmission destination has been changed to the packet switch (PS) # 0 accommodating the communication partner terminal is notified by using a link information transfer packet carrying information necessary for link re-establishment. Notice. The packet switch (PS) # 0 changes the contents of the link memory based on the information of the link information transfer packet.
In the packet switch (PS) # 1 that has received the response of the setting completion from the packet switch (PS) # 0, the destination radio base station (B)
S) A response (connection acceptance) signal is transmitted to # 2m, and a receivable packet is transmitted to the terminal of the communication partner, and communication is resumed.

If, after resuming communication, normal delivery confirmation cannot be performed for the held response-waiting packet due to packet loss due to handover processing or the like,
Retransmission control is performed based on the protocol used. Finally, a disconnection signal is sent to the destination base station (BS) # 1n to release the link used before the movement, and the handover process is completed. In the above description, the case where the mobile terminal communicates with one fixed terminal is described as an example, but communication is possible even if a plurality of logical channels are set. That is, in this case, it can be realized by repeating the regulation process, the takeover process, and the like for the set number of logical channels.

The terminal of the communication partner is not limited to a fixed terminal, but may be a mobile data terminal, a packet terminal connected to another packet network or a telephone network via a gateway exchange, or a non-packet terminal. May be. of course,
Needless to say, there is no need to go through a relay network. As for the handover scheme, the new link scheme has been described as an example here, but the old link scheme may be used. FIG. 3 is a diagram showing a connection configuration for performing a handover based on a packet service uninterrupted handover method according to an embodiment of the present invention. The operation will be described below, focusing on differences from the above-described embodiment.

In this embodiment, the mobile switching center (MSC) #
1 and the same (MSC) # 2 are separate packet switches
The mobile data terminal 10 is connected to the (PS) # 1 and the (PS) # 2, and the mobile data terminal 10 switches mobile communication switching from the cell of the radio base station (BS) # 1n under the mobile communication switching center (MSC) # 1. Station (MS
C) It is assumed that the mobile terminal moves to a cell of a wireless base station (BS) # 2m under the control of # 2. In FIG. 4, the handover request signal transmitted from the mobile data terminal 10 includes a destination radio base station (BS) # 2m and a mobile communication switching center (MSC) # 2
, To the packet switch (PS) # 2. Packet switch (PS) # that has received this handover request signal
2 requests the location register (LR) 9 for processing such as location registration.

The location register (LR) 9 determines the source packet switch (PS) # 1 and performs a handover process to the packet switch (PS) # 2 for the packet switch (PS) # 1. , With the necessary information. Upon receiving the notification, the packet switch (PS) # 1 immediately sends the unreceivable packet to the communication partner terminal, and transmits the communication status, charging information, and the packet waiting for the response to the packet switch (PS) # 2. It is transferred in the call information transfer packet. In the packet switch (PS) # 2, a new link is set based on the information of the call information transfer packet. Hereinafter, it is basically the same as FIG. 2, except that an instruction to release the old link is issued from the packet switch (PS) # 2 to the packet switch (PS) # 1.

FIG. 5 is a diagram showing a connection configuration for performing a handover based on the packet service non-stop interruption handover method according to one embodiment of the present invention. Focusing on differences from the above-described embodiment, the main points of the operation will be described below. The handover from the radio base station (BS) # 1n to the radio base station (BS) # 2m is shown in FIG. 6, and the handover from the radio base station (BS) # 2m to the radio base station (BS) # 3p is shown in FIG. The concept is the same as in the case, and FIGS. 2 and 4 can be basically used for the sequence. However, it is different in that necessary information such as subscriber information and billing information is exchanged between location registers because it spans between operators.

According to the handover method shown in each of the above embodiments, a user who is performing data communication with the mobile data terminal can change the communication area without disconnecting the communication or losing the data. . This is because when both cells before and after the above mobile data terminal move are connected to the same packet switch, they are connected to different mobile communication base stations, and these mobile communication base stations are connected to different packet switches. In this case, the present invention can be applied, for example, when the cell moves across mobile communication networks of different operators. It should be noted that each of the above embodiments is merely an example of the present invention, and it is needless to say that the present invention should not be limited to these.

[0021]

As described above in detail, according to the present invention, there is a remarkable effect that a handover method without interruption of packet service can be realized without losing data during communication. It is.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a connection configuration for performing a handover based on a packet service uninterrupted handover method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a communication sequence according to the embodiment shown in FIG.

FIG. 3 is a diagram illustrating a connection configuration for performing a handover based on a packet service uninterrupted handover method according to a second embodiment of the present invention;

FIG. 4 is a diagram showing a communication sequence according to the embodiment shown in FIG.

FIG. 5 is a diagram illustrating a connection configuration for performing a handover based on a packet service uninterrupted handover method according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a packet network configuration of ISDN.

FIG. 7 is a diagram showing an example of an ISDN packet communication sequence.

FIG. 8 is a diagram illustrating an example of a network configuration of a second generation cordless phone system (PHS).

FIG. 9 is a diagram showing an example of a conventional handover sequence in the system shown in FIG. 8;

[Explanation of symbols]

 1 Packet Network 2 Subscriber Packet Switch (PS) 3 Relay Network 4 Location Register (LR) 5 Packet Terminal 6 Mobile Network 7 Mobile Switching Center (MSC) 8 Radio Base Station (BS) 9 Location Register (LR) 10 Mobile Data terminal

Claims (4)

(57) [Claims] 1. A mobile data terminal communicating via a packet switching network moves to another adjacent cell in a wireless communication unit area (cell) in a mobile communication network connectable to a packet switching network. In this case, the mobile switching center having the source cell under the control thereof is different from the mobile switching center having the destination cell under the control thereof, and both mobile switching centers are connected to the same packet switch. (1) the packet switch, upon receiving the handover request signal transmitted from the mobile data terminal, triggers a layer 3 unreceivable packet to the data terminal that is the communication partner of the mobile data terminal. A first step of transmitting and setting the communication in a regulated state; and (2) a database (b) in which the packet switch performs location registration, authentication, management of subscriber data, and the like of the mobile data terminal. A second step of requesting the update process and the normality check of the information accompanying the handover to the application register, and receiving the response. (3) The packet switch holds the information based on the protocol specification. If the acknowledgment packet that has not been confirmed to be delivered to the mobile data terminal cannot be confirmed after the communication is resumed, retransmission is performed according to a prescribed retransmission procedure, so that the packet corresponds to the communication link used before the handover. A third step of taking over the contents of the retransmission buffer to a retransmission buffer corresponding to a link newly established between the packet switch and the destination cell and holding the retransmission buffer; and (4) the mobile data terminal. Layer 2 and layer 3 call states in the source cell continue on the newly established link between the packet switch and the destination cell. Order to,
A fourth step of taking over call information in the packet switch, and (5) the mobile data terminal after the packet switch performs a new link setting process with a destination cell based on the taken over call information. A fifth step of transmitting a call setting acceptance signal to the packet switch; and (6) the packet switch,
A sixth step of notifying new link information by a link information transfer packet to a packet switch accommodating the data terminal of the communication partner, and (7) a packet switch accommodating the data terminal of the communication partner, A seventh step of transmitting a response packet to the link information transfer packet to the packet switch after changing call information for controlling a destination of the packet based on the link information of the link information transfer packet; (8) After receiving the response packet to the link information transfer packet, the packet switch transmits a response signal to the handover request signal transmitted from the mobile data terminal. Transmitting a packet to release the restricted state of the communication and restart the communication; And (9) after the communication is resumed, if the normal response cannot be confirmed for the response waiting packet held by the packet switch, the packet is retransmitted in accordance with a retransmission procedure specified by the protocol. And (10) a tenth step of releasing the link used by the packet switch before moving, without interruption of the packet service. 2. A mobile data terminal, which is communicating via a packet switching network in a certain cell in a mobile communication network connectable to a packet switching network, moves to another adjacent cell. The source exchange having the original cell and the destination exchange having the destination cell are different, and the source exchange and the destination exchange have different packet exchanges. When the mobile data terminal is connected, (1) the packet exchange (the destination packet exchange) connected to the target communication switching center receives the handover request signal transmitted from the mobile data terminal, and A first step of requesting a location register that performs location registration, authentication, management of subscriber data, etc., to perform information update processing and normality confirmation accompanying handover; and (2) the location The register performs a process associated with the handover, and then, based on the location registration information managed by itself, determines a packet switch (source packet switch) connected to the source communication switching center, and determines the source packet. A second step of transmitting necessary information to the exchange and a signal instructing a handover process; and (3) the source packet switch transmits a layer 3 signal to a data terminal that is a communication partner of the mobile data terminal. After the transmission of the unreceivable packet of the above and the communication in a regulated state, a response signal to the signal instructing the handover process is transmitted to the location register, and the layer 2 and the mobile data terminal in the source cell with the mobile data terminal are transmitted. A response waiting packet whose delivery to the mobile data terminal has not been confirmed is not transferred to the destination packet exchange. A third step of transferring to the destination packet switch by a call information transfer packet to continue the link newly set up with the destination cell by the switch; (4) the destination packet switch includes: From the location register:
After receiving a response signal to the processing request accompanying the handover, a response signal to the call information transfer packet received from the source packet switch is transmitted, and based on the call information inherited from the call information transfer packet, A fourth step of transmitting a call setting acceptance signal to the mobile data terminal after performing a new link setting process between the mobile data terminal and the destination packet switch; and (5) the destination packet switch. Notifies the packet switch accommodating the data terminal of the communication partner of new link information by a link information transfer packet.
And (6) the destination packet switch after the packet switch accommodating the data terminal of the communication partner changes the call information for controlling the destination of the packet based on the link information of the link information transfer packet. A sixth step of transmitting a response packet to the link information transfer packet to the mobile data terminal after the destination packet switch receives the response packet to the link information transfer packet. A response signal to the handover request signal transmitted is transmitted, and on the other hand, a layer 3 receivable packet is transmitted to the data terminal of the communication partner, and the communication is resumed by releasing the regulated state of the communication. Seventh step, (8)
An eighth step of retransmitting the packet in accordance with a retransmission procedure defined by the protocol if normal delivery confirmation of the response waiting packet held by the destination packet switch cannot be performed after the restart of the communication; (9) The ninth release of the link used by the source packet switch before the movement with the mobile data terminal upon receipt of the handover completion notification packet transmitted from the destination packet switch. A non-disruptive handover method for a packet service. 3. A mobile data terminal which is communicating via a packet switching network in a certain cell in a mobile communication network connectable to a packet switching network and moves to another adjacent cell. The mobile communication network operator having the original cell under its control is different from the mobile communication network operator having the destination cell under its control, and the mobile switching centers to which both cells belong are connected to the same packet switch. (1) When the packet switch receives the handover request signal transmitted from the mobile data terminal, the packet switch transmits a layer 3 unreceivable packet to the data terminal that is the communication partner of the mobile data terminal. And (2) a database (b) in which the packet switch performs location registration, authentication, management of subscriber data, and the like of the mobile data terminal. (2) requesting an update process and a normality check of information accompanying the handover with respect to each of the mobile communication registers. The network individually or jointly communicates with the location register to determine whether or not the interconnection conditions between the operators and the contract conditions of the subscriber allow handover. The result and the processing accompanying the handover are determined. A third step of notifying the packet exchange of a response to the request of (a), and (4) the communication of the response waiting packet held by the packet exchange held by the packet exchange based on the protocol definition and not yet confirmed to the mobile data terminal. If acknowledgment is not obtained after resumption of transmission, use it before handover to retransmit according to the specified retransmission procedure. The content of the retransmission buffer corresponding to the communication link that has been transferred to the retransmission buffer corresponding to the link newly set between the packet switch and the destination cell, and is retained.
And (5) in order to continue the layer 2 and layer 3 call states in the source cell of the mobile data terminal even on a link newly set up between the packet switch and the destination cell, A fifth step of taking over call information in the packet switch; and (6) the mobile data terminal after the packet switch performs a new link setting process with a destination cell based on the taken over call information. A sixth step of transmitting a call setting acceptance signal to
(7) a seventh step in which the packet switch notifies the packet switch accommodating the data terminal of the communication partner of new link information by a link information transfer packet; and (8) a data terminal of the communication partner. The packet exchange accommodating the packet information changes the call information for controlling the destination of the packet based on the link information of the link information transfer packet, and then transmits a response packet to the link information transfer packet to the packet exchange. And (9) after receiving the response packet to the link information transfer packet, the packet switch transmits a response signal to the handover request signal transmitted from the mobile data terminal, and Sends a layer 3 receivable packet to the terminal to release the restricted state of the communication. A ninth step of restarting the communication, and (10) after the restart of the communication, if normal delivery confirmation for the response waiting packet held by the packet switch cannot be confirmed, the retransmission procedure specified by the protocol is performed. A tenth step of retransmitting the packet, and (11) information necessary for performing an integrated accounting process between the packet switches, between the packet switch and the location register, or between the location registers. And (12) a twelfth step of releasing a link used by the packet switch before the packet switch travels. 4. A mobile data terminal which is communicating via a packet switching network in a certain cell in a mobile communication network connectable to a packet switching network and moves to another adjacent cell. The mobile communication network operator having the original cell under the control thereof is different from the mobile communication network operator having the target cell under the control of the mobile communication network. When the destination communication switching center to which the cell belongs is connected to a different packet switch, (1) a packet switch (destination packet switching device) connected to the destination communication switching center is transmitted from the mobile data terminal. When the handover request signal is received, the location register that performs location registration, authentication, subscriber data management, and the like of the mobile data terminal performs information update processing and normality confirmation accompanying the handover. A first step of Lai, (2)
The location register that has received the request for processing accompanying the handover communicates with the location register that each of the mobile communication networks individually or jointly operates. A second step of determining whether or not to permit, and notifying the result to the destination packet switch; and (3) a location managed by itself after the location register performs a process associated with handover. On the basis of the registration information, a packet switch (source packet switch) connected to the source communication switching center is determined, and necessary information and a signal for instructing a handover process are transmitted to the source packet switch. Step 3; and (4) the source packet switch performs layer communication with a data terminal that is a communication partner of the mobile data terminal. And of sending a Not Ready packet,
After the communication is restricted, a response signal to the signal instructing the handover process is transmitted to the location register, and the call state of Layer 2 and Layer 3 with the mobile data terminal in the source cell and the charging information And the response waiting packet whose delivery with the mobile data terminal has not been confirmed continues even on a link newly set up with the target cell in the target packet switch,
A fourth step of transferring a call information transfer packet to the destination packet switch; and (5) the destination packet switch receives, from the location register, a response signal to a processing request accompanying a handover, and A response signal to the call information transfer packet received from the packet switch is transmitted, and a new link is set up between the mobile data terminal and the target packet switch in the target cell based on the call information inherited from the call information transfer packet. After performing the processing, a fifth step of transmitting a call setting acceptance signal to the mobile data terminal; and (6) the destination packet switch transmits to the packet switch accommodating the communication partner data terminal. A sixth step of notifying new link information by a link information transfer packet;
(7) after the packet switch accommodating the data terminal of the communication partner changes the call information for controlling the destination of the packet based on the link information of the link information transfer packet, A seventh step of transmitting a response packet to the link information transfer packet; and (8) a handover request signal transmitted from the mobile data terminal after the destination packet switch receives the response packet to the link information transfer packet. And transmitting a response signal to the data terminal of the other party to transmit a layer 3 receivable packet, and releasing the restricted state of the communication to resume the communication. And (9) responding to the response waiting packet held by the destination packet switch after the communication is resumed. If normal delivery confirmation cannot be performed, a ninth step of retransmitting the packet according to a retransmission procedure defined by a protocol, and (10) between the packet switches, between the packet switch and the location register, or A tenth step of communicating information necessary for performing integrated accounting between the location registers; and (11) the source packet switch transmits a handover completion notification packet transmitted from the destination packet switch. An eleventh step of releasing a link used before movement with the mobile data terminal upon receipt of the packet data.