JP2002152835A - Mobile terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the throughput of the entire network by suppressing deterioration of a wireless channel state and a TCP(Transmission Control Protocol) segment addressed to a mobile terminal during hand-over processing but unable to arrive at the mobile terminal. SOLUTION: A mobile terminal 80 makes wireless communications with a base station via a wireless I/F section 81. An electric field strength measurement means 86 is connected to the wireless I/F section 81 and measures a reception electric field strength through the wireless I/F section 81. The mobile terminal 80 grasps a channel state on the basis of the transition of the measured reception electric field strength, transfers the grasped state to a communication line control means 85 to reflect the state on link control with a TCP processing section 83. As a result, a pseudo congestion state is generated so that a TCP link is not interrupted during data transmission and the data transmission can be restarted smoothly when the wireless channel is again restored to an excellent state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a wireless Internet access system in which a base station and a mobile terminal can enjoy an Internet service through wireless communication, and performs a communication method for realizing efficient data transmission. Related to a mobile terminal device.

[0002]

2. Description of the Related Art An Internet communication protocol TCP (Transmi) designed for use in a wired fixed network.
session Control Protocol) / IP
In order to use (Internet Protocol) in a wireless mobile network, various studies are underway.

As an example of a conventional wireless access system, Japanese Patent Laid-Open Publication No. Hei 10-336751 discloses a wireless communication system in which a wireless line is disconnected every time a TCP sequence ends for the purpose of effective use of the line.

Hereinafter, a conventional wireless access system will be described with reference to FIG.

FIG. 10 is a diagram for explaining a communication sequence in a conventional radio access system.
Represents the HTTP protocol of the mobile terminal, 502 represents the TCP of the mobile terminal, 503 represents the wireless layer of the mobile terminal, 504 represents the wireless layer of the base station, 505 represents the TCP of the server, and 506 represents the HTTP of the server.

[0006] The HTTP access of the conventional wireless access system in the above protocol configuration will be described in time series below. When the Web browser is activated and access is started, the HTTP protocol 501 is activated. Accordingly, the TCP 502 is activated, and the connection processing of the wireless line is performed between the wireless layers 503 and 504. The mobile terminal wireless layer 503 transmits a channel request to the base station wireless layer 504, and when a vacant channel is detected, the base station wireless layer 504 allocates a channel and connects a wireless line.

Subsequently, a link connection process between TCPs 502-505 is performed. That is, the mobile terminal TCP50
2 transmits the SYN packet to the server TCP5.
05 responds with a SYN packet and the mobile terminal TCP 50
2 finally sends an ACK, thereby completing the connection of the TCP link. With this, the HTTP protocol is connected between the mobile terminal and the server, and Web access becomes possible.

When a series of Web access ends, TC
The P link is disconnected. That is, the mobile terminal TCP50
2 sends a FIN packet to the server TCP 505
Responds with an ACK packet. Continue with server TCP5
05 transmits a FIN packet and the mobile terminal TCP 502
ACK response completes the disconnection of the TCP link. When the TCP link is disconnected, the wireless layer 503 of the mobile terminal issues a channel disconnection request, and the wireless layer 504 of the base station disconnects the wireless line according to the request. The next time the Web access is performed, the process is again performed from the wireless line connection processing.

[0009] In the above-mentioned conventional example, an object of the present invention is to avoid a situation in which the wireless line is disconnected when the TCP link is disconnected, and the wireless line remains connected despite no transmission / reception data.

[0010]

In the above-described conventional radio access system, it is assumed that communication can be performed without any problem during a series of data periods in which applications on the TCP protocol communicate. However, if the radio link is forcibly disconnected due to deterioration of the radio link status or handover during the communication data period, the following problems occur.

Since the server cannot know that the wireless line has been disconnected, it continues to transmit TCP segments as before. However, the mobile terminal is not reached, and as a result, AC
The retransmission process is performed after waiting for a timeout because K packets cannot be received. Therefore, if the wireless link status does not recover even after waiting for a long time, or if the handover process requires time, a retransmission packet is periodically transmitted from the server, which may reduce the line efficiency.

As an example, a radio access system having a configuration as shown in FIG. 5 will be described. Here, FIG. 5 is a schematic diagram showing a spot-type communication system such as a millimeter-wave access system, where 20 to 22 are base stations, 80 is a mobile terminal, 1 is a base station antenna, and 2 to 4 are base station antennas 1.
, 5 denotes a route control station accommodating the base stations 20 to 22, and 60 denotes a backbone network.

The mobile terminal 80 is located in the wireless communication area 2 and uses the TCP / IP protocol to connect to the network 60.
Access to a server (not shown). At this time, the signal passes through the base station 20 and the route control station 5. Communication area 2 while mobile terminal 80 is accessing the server
, The server continues to transmit data without knowing that the mobile terminal 80 has become inaccessible. At this time, since the server's TCP protocol cannot receive the ACK packet from the mobile terminal 80,
Wait for timeout and execute retransmission processing. However, since the mobile terminal 80 has a distance (time) until it arrives at the next area 3 where wireless communication is possible, communication cannot be immediately resumed. That is, the TCP protocol of the server repeats retransmission for a while and then forcibly disconnects the TCP link.

As described above, since the server repeatedly transmits unreachable packets, the line efficiency is reduced. In addition, the processing efficiency of the server itself is reduced, resulting in an increase in the load on the entire network.

An object of the present invention is to solve the above-mentioned problems, and to suppress the deterioration of the radio channel condition and the unreachable TCP segment addressed to the mobile terminal during the handover process, and to improve the throughput of the entire network. Things.

[0016]

In order to solve the above-mentioned problems, according to the present invention, a function is provided for monitoring the status of a radio channel in a mobile terminal device, and a TCP is provided based on the channel status obtained from the function.
Perform link control. That is, the received electric field strength, CR
TC based on information such as C error rate and handover trigger
The user selects whether to continue transmission / reception of the P-segment, perform parameter control such as temporarily interrupting the transmission, or disconnect the TCP link and completely stop the transmission.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention is directed to a mobile terminal device which accesses the Internet by wirelessly communicating with a base station. The present invention discloses a mobile terminal device characterized by having communication link control means for judging communication maintenance, temporary interruption or cancellation according to the following conditions. The access is maintained as it is, and when it is determined that the radio link condition is deteriorated, the throughput of the TCP link is remarkably reduced to suspend the pseudo link temporarily, or when it is clear that the radio link condition will not recover for a long time, the TCP link Is controlled to be disconnected, transmission of unreachable packets from the server can be suppressed.

According to a second aspect of the present invention, there is provided an electric field intensity measuring means for periodically measuring a received electric field intensity value,
2. The mobile terminal device according to claim 1, wherein said communication link control means operates by receiving a received electric field strength value signal generated by said electric field strength measuring means as an input. Since the reception rate also decreases, accurate TCP link control can be performed by making a determination of temporary suspension or link disconnection based on the received electric field strength.

According to a third aspect of the present invention, there is provided an error rate measuring means for periodically measuring an error rate from an error control field included in a radio frame, and wherein the communication link control means comprises the 2. The mobile terminal device according to claim 1, wherein the mobile terminal device operates by using an error status signal generated by the rate measuring means as an input.
By performing a temporary interruption or link disconnection determination based on the frame error rate obtained as a result of the RC error test,
Accurate TCP link control can be performed.

According to a fourth aspect of the present invention, there is provided a handover determining means for generating a handover trigger signal as handover timing, wherein the communication link control means operates with the handover trigger signal as an input. The mobile terminal device according to claim 1, wherein in the wireless system in which the mobile terminal performs the handover determination mainly by the mobile terminal, the temporary stop or the link disconnection is performed based on the handover trigger indicating the switching of the communication area or the exit timing. By making the determination, accurate TCP link control can be performed, and information about the surrounding base stations can be obtained. If it is known that the vehicle will not enter the communication area for a long time in the future, only link disconnection is performed. It can be controlled as follows.

The invention according to claim 5 of the present invention operates when the communication link control means detects a handover trigger signal received from a base station. In a wireless system of a system in which the base station performs the handover determination mainly by the base station, the temporary stop or the link disconnection is determined based on the handover trigger indicating the switching or the exit timing of the communication area received from the base station. , Accurate TC
P-link control can be performed, and information on the surrounding base stations can be obtained or given along with a handover trigger. If it is known that the terminal will not enter the communication area for a long time in the future, only link disconnection is performed. It can also be controlled to do so.

According to a sixth aspect of the present invention, when the communication link control means determines that the radio link condition has deteriorated by a certain degree or more, the TCP window size is set to 0 or close to 0 as interruption control for the transport layer. The mobile terminal device according to any one of claims 2 to 6, wherein a packet to be set to a value is transmitted, and a wireless line is disconnected by setting a packet transmission interval of a server to be extremely long. During this period, the amount of packets transmitted by the server can be suppressed, and the line efficiency can be improved.

According to a seventh aspect of the present invention, when the communication link control means determines that the radio link condition has deteriorated by a certain amount or more, the transmission interval of the ACK signal is gradually increased as interruption control for the transport layer. The mobile terminal device according to any one of claims 2 to 6, wherein the transmission is stopped as a result.
By generating a pseudo-congestion state so that the reception interval of the CK packet becomes longer, the retransmission interval by the server becomes longer, and as a result, the packet transmission amount of the server while the wireless line is disconnected is suppressed, Line efficiency can be improved.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG.

(Embodiment 1) A first embodiment will be described with reference to FIGS.

FIG. 1 is a schematic diagram showing a configuration of a first mobile terminal device according to the present invention. In FIG. 1, 80 is a mobile terminal device, 81 is a wireless I / F unit, 82 is an IP processing unit, 83
Is a TCP processing unit, 84 is an application processing unit, 85
Denotes communication link control means, and 86 denotes electric field strength measurement means.

FIG. 6 is a schematic diagram showing a wireless access system using a mobile terminal device according to the present invention. In FIG. 6, reference numeral 80 denotes a mobile terminal, 20 denotes a base station, and 60 denotes a backbone network.

FIG. 7 is a conceptual diagram showing the transition of the received electric field strength measured in the mobile terminal device according to the present invention. 7, reference numeral 91 denotes a vertical axis representing the received electric field strength, 92 denotes a horizontal axis representing the time, 94 denotes a transition of the received electric field strength, 95 denotes a boundary value line for judging a deteriorated state, and 96 denotes a transition 94 and a boundary value. The time when the line 95 crosses is shown.

The operation of the above configuration will be described below. The wireless access system according to the present embodiment has a configuration shown in FIG. That is, the mobile terminal 80 communicates with the base station 20 via a wireless line, and further accesses a server (not shown) in the backbone network 60.

The configuration of the mobile terminal 80 is as shown in FIG. 1, and wireless communication with the base station is performed via the wireless I / F unit 81. The wireless I / F unit 81 is connected to the IP processing unit 82 as an upper layer, and the IP processing unit 82
The CP processing unit 83 and the TCP processing unit 83 are connected to the application processing unit 84 as an upper layer. Also,
The electric field strength measuring means 86 is connected to the wireless I / F section 81,
The received electric field strength is measured via the wireless I / F unit 81.
The information on the received electric field strength measured by the electric field strength measuring means 86 is transferred to the communication link control means 85 and reflected on the TCP link control.

Hereinafter, the operation of the communication link control means 85 in the present embodiment will be described. FIG. 7 shows an example of the transition of the received electric field strength acquired by the communication link control means 85. The transition 94 peaks at a certain time and gradually decreases in intensity. The communication link control means 85 monitors the transition 94 with time, and the rate of change is negative, and the time 96 when the rate falls below the receivable electric field strength boundary 95 determined in advance in view of the characteristics of the wireless I / F unit 86. , Or at a time when the time reaches the vicinity thereof, the deterioration of the wireless channel condition is determined, and the control for temporarily suspending or stopping the connected TCP link is activated. Here, the control of the temporary suspension is applied when data transmission is in progress, and the suspension, that is, the TCP
The link disconnection control is applied when data transmission has already been completed.

Note that the boundary value 95 may include a margin in consideration of the time required for the TCP link control to operate sufficiently.

Next, a method for temporarily suspending the TCP link will be described below. A first method for suspending a TCP link is to set the TCP reception window size to 0.
Alternatively, a packet having a value close to 0 is transmitted. When the server receives a packet with a requested window size of 0 or a value close to 0, the server sets the destination terminal (mobile terminal 8).
It detects that the reception capacity of 0) has decreased, and operates to suppress transmission packets. In particular, when the window size is 0, the transmission to the mobile terminal 80 is stopped, except that one octet of data is periodically retransmitted in accordance with the long-time timer of the TCP protocol. After a while, when the radio line condition becomes good and communication becomes possible, the mobile terminal 80 transmits a packet with a window size of 0 or more to the server,
The server will operate to resume the previously stopped transmission.

As a second method for temporarily interrupting the TCP link, transmission of an ACK packet for a TCP segment received from a server is intentionally delayed, and the transmission interval is extended to finally transmit an ACK packet. It is not to be. The server operates to set the retransmission timer based on the transmission time of the TCP segment and the reception time of the corresponding ACK packet. This is TC
It is determined that the congestion degree of the network increases as the time from the transmission of the P segment to the reception of the ACK packet increases, and the time until the retransmission, that is, the set value of the retransmission timer is largely corrected.

When the communication link control means 85 detects that the radio link condition will deteriorate in the future, the receiving TC
The transmission of the ACK packet for the P segment is gradually delayed, and the transmission is stopped when the ACK packet is transmitted several times. As a result, the server determines that rapid congestion has occurred, sets the retransmission timer to a large value, and suppresses transmission of unreachable TCP segments while the wireless line is disconnected. After a while, when the radio line condition becomes good and communication becomes possible, the mobile terminal 8
0 only needs to continue transmitting the ACK packet for the received TCP segment without delay.

As a method for stopping or disconnecting the TCP link, it is only necessary to transmit a packet in which the FIN flag is set to ON.

As described above, according to the first embodiment, the mobile terminal detects the deterioration of the radio channel condition based on the received electric field strength, and as a result, the control for temporarily suspending or stopping the transmission of the TCP segment from the server. By doing so, it is possible to suppress the transmission of unreachable packets while the wireless line is virtually disconnected, and to improve the utilization efficiency of the network.

In the configuration of the first embodiment,
Although the example in which the application processing unit 84 and the TCP processing unit 83 have a direct interface is shown and used, this does not prevent insertion of another protocol processing unit between them.

(Embodiment 2) A second embodiment will be described with reference to FIGS.

FIG. 2 is a schematic diagram showing a configuration of a mobile terminal device according to the second embodiment of the present invention. 2, reference numeral 80 denotes a mobile terminal device; 81, a wireless I / F unit;
2 denotes an IP processing unit, 83 denotes a TCP processing unit, 84 denotes an application processing unit, 85 denotes a communication link control unit, and 87 denotes an error rate measurement unit.

FIG. 8 is a conceptual diagram showing the transition of the CRC error rate measured in the mobile terminal device according to the present invention. 8, 97 is the vertical axis representing the number of error frames, 92 is the horizontal axis representing time, 98 is the transition of the number of error frames, 99 is the boundary value line for judging the deterioration state, and 100 is the transition 98
And the time when the boundary value line 99 intersects.

The operation of the above configuration will be described below. The configuration of the wireless access system according to the second embodiment is the same as that described with reference to FIG. 6 in the first embodiment.

The configuration of the mobile terminal 80 is as shown in FIG. 2, and wireless communication with the base station is performed via the wireless I / F unit 81. The wireless I / F unit 81 is connected to the IP processing unit 82 as an upper layer, and the IP processing unit 82
The CP processing unit 83 and the TCP processing unit 83 are connected to the application processing unit 84 as an upper layer. Also,
The error rate measuring unit 87 is connected to the wireless I / F unit 81, receives the CRC test result of the wireless frame received by the wireless I / F unit 81, and calculates the number of error frames. Information about the number of error frames calculated by the error rate measuring means 87 is transferred to the communication link control means 85 and reflected in TCP link control.

Hereinafter, the operation of the communication link control means 85 in the present embodiment will be described. FIG. 8 shows an example of the transition of the number of error frames acquired by the communication link control means 85. The transition 98 shows an upward trend at a certain time. The communication link control means 85 changes with time 98
At a time 100 when the rate of change is positive and exceeds an error frame number boundary 99 capable of maintaining a wireless channel determined in advance in consideration of the characteristics of the wireless I / F unit 86 and the characteristics of the system, or At a time when the time has reached the vicinity, it is determined that the wireless channel condition has deteriorated, and control for temporarily suspending or stopping the connected TCP link is activated. Here, the control of the temporary interruption is applied when the data transmission is in progress, and the stop, that is, the control of the TCP link disconnection, is applied when the data transmission is already completed.

Note that the boundary value 99 may include a margin in consideration of the time for which the TCP link control can sufficiently operate.

The same method as that described in the first embodiment can be used as a method for temporarily suspending and stopping TCP link control.

As described above, according to the second embodiment, the mobile terminal detects the deterioration of the radio channel condition based on the number of error frames as the CRC test result, and as a result, the T
By performing control to temporarily suspend or stop the transmission of the CP segment, it is possible to suppress transmission of an unreachable packet while the wireless line is actually disconnected, and to improve network utilization efficiency.

In the configuration of the second embodiment,
Although the example in which the application processing unit 84 and the TCP processing unit 83 have a direct interface is shown and used, this does not prevent insertion of another protocol processing unit between them.

(Embodiment 3) A third embodiment will be described with reference to FIGS. 3 to 6 and FIG.

FIG. 3 is a schematic diagram showing the configuration of the third mobile terminal device according to the present invention. In FIG. 3, 80 is a mobile terminal device, 81 is a wireless I / F unit, 82 is an IP processing unit,
83 is a TCP processing unit, 84 is an application processing unit,
Reference numeral 85 denotes a communication link control unit, and 88 denotes a handover determination unit.

FIG. 4 is a schematic diagram showing the configuration of the fourth mobile terminal device according to the present invention. All the assigned numbers in FIG. 4 are the same as those in FIG.

FIG. 5 is a diagram for explaining an application example of the radio access system using the mobile terminal device according to the third embodiment shown in FIGS. 3 and 4. In FIG.
Reference numeral 80 denotes a mobile terminal device, reference numerals 20 to 22 denote base stations, reference numeral 1 denotes a base station antenna, reference numerals 2 to 4 denote wireless communication areas formed by the base station antennas 1, reference numeral 5 denotes a path control station accommodating the base stations 20 to 22, Reference numeral 60 denotes a backbone network.

FIG. 9 is a conceptual diagram showing a handover trigger signal in the mobile terminal device according to the present invention. 9, reference numeral 101 denotes a vertical axis representing a signal voltage, 92 represents a horizontal axis representing time, 102 represents a voltage transition of a handover trigger signal, 1
03 indicates the time when the voltage transition changes due to the occurrence of the handover trigger.

The operation of the above configuration will be described below. The configuration of the wireless access system according to the present embodiment is the same as that described with reference to FIG. 6 in the first embodiment.

The configuration of the mobile terminal 80 is as shown in FIG. 3, and wireless communication with the base station is performed via the wireless I / F unit 81. The wireless I / F unit 81 is connected to the IP processing unit 82 as an upper layer, and the IP processing unit 82
The CP processing unit 83 and the TCP processing unit 83 are connected to the application processing unit 84 as an upper layer. Also,
The handover determination unit 88 is connected to the wireless I / F unit 81 and generates a handover trigger signal that triggers movement in the wireless communication area. The handover trigger signal generated by the handover determination means 88 is transmitted to the communication link control means 8.
5 and reflected in TCP link control.

Hereinafter, the operation of the communication link control means 85 in the present embodiment will be described. FIG. 9 shows an example of the transition of the handover trigger signal acquired by the communication link control means 85. The transition 102 forms a trigger pulse that prompts the start of the handover process at a certain time. The communication link control unit 85 monitors the transition 102 with the time, detects that the wireless line is disconnected at the time 103 when the trigger pulse is detected, and sets the connected TCP.
Activate the control to suspend or cancel the link.
Here, the control of the temporary suspension is applied when data transmission is being performed, and the suspension, that is, the control of disconnecting the TCP link, has been determined that the data transmission has already been completed or that the time until moving to the next base station is long. Apply to cases.

As an example, a case where the cancellation is determined will be described with reference to FIG. In the wireless access system shown in FIG. 5, base stations are arranged on spots. That is, since there is no overlap between the communication areas 2 to 4,
It is characterized in that the time from leaving the communication area 2 to entering the communication area 3 is longer than that of the conventional wireless system. Therefore, if the time from leaving the communication area 2 to entering the next communication area 3 is very long, holding the TCP link increases the load on the server and wastes limited resources. It will also be.
Therefore, information such as base station arrangement is obtained in advance, and when it is determined that the time until entry into the next communication area is extremely long, the control for disconnecting the TCP link even during communication is activated. And effective use of resources.

The same method as that described in the first embodiment can be used as a method for temporarily suspending and stopping TCP link control.

For a radio access system to which a method of starting a handover process by receiving a handover trigger from a base station is applied, the mobile terminal device 80 having the configuration shown in FIG.
By directly transferring the handover trigger signal 102 to be generated by the wireless communication unit 8 from the wireless I / F unit 81 to the communication link control unit 85, the characteristics according to the present invention can be sufficiently obtained by the same operation as described above. is there.

As described above, according to the third embodiment, the mobile terminal detects that the radio line is disconnected based on the handover trigger signal, and as a result, temporarily suspends or stops the transmission of the TCP segment from the server. By performing such control, it is possible to suppress transmission of unreachable packets while the wireless line is disconnected, and to improve network utilization efficiency.

In the configuration of the third embodiment,
Although the example in which the application processing unit 84 and the TCP processing unit 83 have a direct interface is shown and used, this does not prevent insertion of another protocol processing unit between them.

[0062]

According to the present invention, a mobile terminal which detects that a radio link is degraded due to deterioration of a radio link or a handover is controlled so that a TCP window size is set very small in advance or a TCP link is cut. By doing so, it is possible to prevent the server from repeatedly transmitting unreachable packets, thereby improving the line efficiency. In addition, it is possible to prevent the processing efficiency of the server from being reduced by repeating retransmission, which leads to a reduction in the load on the entire network.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a first mobile terminal device according to the present invention.

FIG. 2 is a schematic diagram showing a configuration of a second mobile terminal device according to the present invention.

FIG. 3 is a schematic diagram showing a configuration of a third mobile terminal device according to the present invention.

FIG. 4 is a schematic diagram showing a configuration of a fourth mobile terminal device according to the present invention.

FIG. 5 is a diagram for explaining an application example of a wireless access system using a mobile terminal device according to the present invention.

FIG. 6 is a schematic diagram showing a configuration of a wireless access system using a mobile terminal device according to the present invention.

FIG. 7 is a conceptual diagram showing a transition of a received electric field strength measured in the mobile terminal device according to the present invention.

FIG. 8 is a conceptual diagram showing a transition of a CRC error rate measured in the mobile terminal device according to the present invention.

FIG. 9 is a conceptual diagram showing a handover trigger signal in the mobile terminal device according to the present invention.

FIG. 10 is a diagram for explaining a communication sequence in a conventional wireless access system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base station antenna 2, 3, 4 Wireless communication area 5 Route control station 20, 21, 22 Base station 60 Backbone network 80 Mobile terminal device 81 Wireless I / F unit 82 IP processing unit 83 TCP processing unit 84 Application processing unit 85 Communication Link control means 86 Electric field strength measuring means 87 Error rate measuring means 88 Handover judgment means 91 Received electric field strength axis 92 Time axis 94, 98, 102 Transition 95, 99 Boundary value 96, 100, 103 Judgment time

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04Q 7/04 K F Term (Reference) 5K030 GA03 HA04 JL01 JL07 JT02 KA01 LB05 5K033 AA01 BA01 BA02 CB08 DA15 DA19 DB14 5K067 AA11 BB21 DD24 DD36 DD44 DD46 EE02 EE10 EE16 FF16 HH01 JJ39

Claims (7)

[Claims] 1. A mobile terminal device that accesses the Internet by wirelessly communicating with a base station.
A mobile terminal device comprising communication link control means for judging whether to maintain, temporarily suspend, or stop communication with a transport layer according to a hierarchy according to a radio channel condition. 2. The method according to claim 1, further comprising: a field strength measuring unit for periodically measuring a received field strength value, wherein the communication link control means operates by using a received field strength value signal generated by the field strength measuring means as an input. The mobile terminal device according to claim 1, wherein 3. An error rate measuring means for periodically measuring an error rate from an error control field included in a radio frame, wherein the communication link control means transmits an error status signal generated by the error rate measuring means. The mobile terminal device according to claim 1, wherein the mobile terminal device operates as an input. 4. The mobile terminal device according to claim 1, further comprising a handover determination unit that generates a handover trigger signal as a handover timing, wherein the communication link control unit operates using the handover trigger signal as an input. . 5. The mobile terminal device according to claim 1, wherein said mobile terminal device operates when said communication link control means detects a handover trigger signal received from a base station. 6. When the communication link control means determines that the radio link condition has deteriorated by a certain amount or more, a packet for setting a TCP window size to 0 or a value close to 0 is transmitted as interruption control for the transport layer. The mobile terminal device according to any one of claims 2 to 6, wherein: 7. When the communication link control means determines that the radio link condition has deteriorated by a certain amount or more, the transmission interval of the ACK signal is gradually increased as interruption control for the transport layer, and as a result, transmission is stopped. The mobile terminal device according to any one of claims 2 to 6, wherein: