JP4832483B2 - Mobile communication system and mobile communication method - Google Patents

Description

  The present invention relates to a mobile communication device and a mobile communication method for transmitting and receiving data between a mobile and a ground station.

  Conventionally, in data communication such as TCP (Transmission Control Protocol) in which packets are transmitted and received while a response is confirmed between a transmission terminal and a reception terminal, a method for improving communication throughput is disclosed in, for example, [Patent Document 1]. The described retransmission control method is known.

  In this method, the receiving terminal estimates the retransmission timeout time of the transmitting terminal from the round-trip delay time between the transmitting terminal and the receiving terminal (hereinafter referred to as RTT, which is an abbreviation of Round Trip Time) measured during communication. When the receiving terminal does not receive the next packet even after the retransmission timeout period has elapsed from the time when the packet is received from the transmitting terminal, the receiving terminal determines that the next packet has been lost in the transmission path, In this method, a packet (segment promotion signal) that prompts retransmission is transmitted to the transmission terminal.

  When there is a packet to be retransmitted, the transmitting terminal that has received the segment promotion signal retransmits the packet to be retransmitted to the receiving terminal, and transmits a dataless signal when there is no packet to be retransmitted.

  In this way, retransmission of lost packets is realized early, and communication throughput is improved.

JP 2007-274206 A

  A mobile communication system, that is, a communication system in which one of transmission / reception terminals exists on a mobile body and the other exists on the ground, or communication in which transmission / reception terminals exist on different mobile bodies and communicate via a ground communication network In the system, a communication interruption period occurs due to handover, but when wireless communication is recovered after the communication interruption period ends, it is necessary to restart packet transmission / reception as soon as possible.

  However, in a communication system with a large RTT, the first retransmission timeout time may be longer than the communication interruption period due to the handover, and after the retransmission timeout time elapses as in the conventional technique described in [Patent Document 1]. When the transmission terminal is urged to retransmit the packet, there is a long period in which the packet cannot be transmitted / received immediately after the end of the communication interruption period until the packet is retransmitted, the utilization efficiency of the wireless transmission path is reduced, and the communication throughput is reduced. There is a problem of lowering.

  Further, when a plurality of applications having different RTTs perform TCP communication in parallel, in the above conventional technique, retransmission is started in the order of packets of applications having a short retransmission timeout time. There is also a problem of unfairness.

  In addition, the above-mentioned conventional technology needs to implement a round trip time measuring unit, a retransmission timeout time calculating unit, a segment promotion transmitting unit, etc. in the transmitting and receiving terminals, but in communications performed between a large number of unspecified terminals such as Internet access. It is not practical to install in all the transmitting / receiving terminals that can be accessed.

A first object of the present invention is to provide a mobile communication system and a mobile communication method that can retransmit a data packet without waiting for an RTT, improve the utilization efficiency of a wireless transmission path, and improve communication throughput. There is to do.

The second object of the present invention is to perform relay processing that causes a transmitting terminal to retransmit a packet immediately after recovery of wireless communication after the end of a communication interruption period due to handover. An object of the present invention is to provide a mobile communication system and a mobile communication method capable of improving the use efficiency of a wireless transmission path and improving the communication throughput even in TCP communication performed between terminals.

  In order to achieve the above object, the present invention provides a relay device for relaying packets transmitted and received between the ground side and a mobile unit, a ground side relay device connected to a ground side radio, and a mobile unit side radio. Each relay device is connected to a transmitting terminal side or a receiving terminal via a communication network, and each relay device receives a packet (acknowledgment response packet) received from the wireless device side. ACK packet that stores the latest acknowledgment packet (hereinafter referred to as ACK packet) of TCP communication that relays from the receiving terminal side to the wireless device side. It comprises storage means and radio link monitoring means for monitoring the connection state of the radio link between the ground side radio device and the mobile side radio device.

  The wireless link monitoring means detects the connection state of the wireless link by monitoring the wireless transmission path between the ground side relay device and the mobile side relay device, and the packet relay means detects all packets received from the wireless device side. When the wireless link monitoring means detects that the wireless link is in a connected state, it relays it directly to the transmitting terminal side or the receiving terminal side. When the wireless link monitoring means detects that the wireless link is disconnected, the data packet is discarded, and the ACK packet storage means stores the latest ACK packet received from the receiving terminal side, and the wireless link is disconnected from the disconnected state. When the wireless link monitoring means detects that the connection state has been restored, the stored ACK packet is duplicated and transmitted to the relay device on the data packet transmission side for the designated number of times. The terminal that has received the ACK packet determines a data packet to be transmitted including a data packet to be retransmitted based on the received ACK packet.

  According to the present invention, even when TCP communication is performed between a large number of unspecified terminals such as Internet access in mobile communication, it is possible to improve the use efficiency of a wireless transmission path and improve communication throughput. A body communication device and a mobile communication method can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the “moving object” refers to a train, bus, aircraft, ship, automobile, terminal carried by a moving person, and the like.

  A first embodiment will be described. FIG. 1 is a configuration diagram of a mobile communication system according to the present embodiment.

  The mobile communication system shown in FIG. 1 is configured as follows. A ground terminal 1 installed on the ground side and performing data transmission / reception and a plurality of ground stations 3 are connected via a ground data transmission path 2. The ground station 3 includes a ground station relay device 30 connected to the ground data transmission path 2, a ground station radio 31 that performs wireless communication with the mobile body 4, and a ground station antenna 32 that transmits and receives radio waves.

  The mobile unit 4 includes a mobile terminal 41 that transmits and receives data, a mobile station 43, and a mobile unit data transmission path 42 that connects the mobile terminal 41 and the mobile station 43. The mobile unit 4 includes a mobile station relay device 430 connected to the mobile unit data transmission path 42, a mobile station radio 431 that performs radio communication with the ground station 3, and a mobile station antenna 432 that transmits and receives radio waves. .

  Here, the ground terminal 1 and the mobile terminal 41 are transmission / reception terminals, and use a protocol capable of confirming data delivery by an acknowledgment packet (referred to as an ACK packet) such as TCP which is a transport layer communication protocol. .

  There may be a plurality of ground terminals 1 and mobile terminals 41, and each terminal is identified by, for example, an IP (Internet Protocol) address. The ground terminal 1 and the mobile terminal 41 having the same structure may communicate with each other by a plurality of different applications, and each communication connection is identified by, for example, a combination of an IP address and a port number. A plurality of mobile bodies 4 may exist, and each mobile body is identified by, for example, the MAC (Media Access Control) address of the mobile station radio 431 or the IP address of the mobile station relay device 430.

  The ground station relay device 30 stores packet relay means for relaying packets received from the ground station radio 31 to the ground terminal 1 and the latest ACK packet of TCP communication relayed from the ground terminal 1 to the ground station radio 31. ACK packet storage means, and radio link monitoring means for constantly monitoring the connection state of the radio link between the ground station radio 31 and the mobile station radio 431.

  The mobile station relay device 430 relays the packet received from the mobile station radio 431 to the mobile terminal 41 and the latest ACK packet of the TCP communication relayed from the mobile terminal 41 to the mobile station radio 431. ACK packet storage means for storing the wireless link, and wireless link monitoring means for constantly monitoring the connection state of the wireless link between the mobile station radio 431 and the ground station radio 31.

  The radio link monitoring means detects the connection state of the radio link, for example, data issued by an echo request function and an echo response function which are one function of ICMP (Internet Control Message Protocol) defined in RFC 792 of IETF. Is used.

  The ground station relay device 30 and the mobile station relay device 430 express the function of each means described above with a logical symbol, and make it LSI by an FPGA (Field Programmable Gate Array) or operate each function in parallel by a network processor or the like. It is realized with.

  In addition, the ground station relay device 30 and the mobile station relay device 430 can be realized by software operating on a computer having a CPU (Central Processing Unit), and a hardware configuration example in that case is shown in FIG.

  As shown in FIG. 2, the ground station relay device 30 and the mobile station relay device 430 input a setting item and an arithmetic device 600 equipped with a CPU, a cache memory, a main memory, and the like that perform the above-described processing. Input device 601 such as a switch or keyboard, confirmation when setting items are input, output device 602 such as an LED display or a liquid crystal panel for displaying an operation state and log information, and storing packets and log information Packet transmission / reception between the storage device 603 such as a hard disk, silicon disk, or non-volatile memory, the terrestrial data transmission path 2, the mobile data transmission path 42, and the ground station radio 31 or mobile station radio 431. It comprises a plurality of external interface devices 604 having interface functions to be performed.

  Below, the case where the ground station relay apparatus 30 and the mobile station relay apparatus 430 are implement | achieved in the software which operate | moves on the computer shown in FIG. 2 is demonstrated as an example.

  The terrestrial data transmission path 2 and the mobile data transmission path 42 use, for example, wired transmission means such as Ethernet (registered trademark) and ATM (Asynchronous Transfer Mode), or wireless transmission such as wireless LAN conforming to the IEEE 802.11 standard. Using means. Further, a network is configured by combining wired transmission means or wireless transmission means, a switching hub, a router, and a WAN (Wide Area Network).

  The ground station radio 31 and the mobile station radio 431 use, for example, a radio communication device such as a radio transceiver conforming to the IEEE 802.11 standard or a radio transceiver conforming to the IEEE 802.16 standard, or an electrical signal is converted into a radio signal. You are using a media converter that converts between them.

  The operation procedure in the ground station relay device 30 or the mobile station relay device 430 will be described with reference to FIG.

  The operation procedure shown in FIG. 3 is common to the ground station relay device 30 and the mobile station relay device 430. If the operation is the operation of the ground station relay device 30, the “transmission path” is the terrestrial data transmission path 2, the “radio device” "Means the ground station radio 31, and in the operation of the mobile station relay device 430,“ transmission path ”means the mobile data transmission path 42, and“ radio equipment ”means the mobile station radio 431.

  When the packet relay means receives the ACK packet from the transmission path (procedure 9001), the ACK packet accumulation means accumulates the received ACK packet in the TCP session (procedure 9002), and the radio link monitoring means disconnects the radio link. If it is detected that it is not in the state, that is, it is in the connected state (procedure 9003), the packet relay means relays the received ACK packet to the radio equipment (procedure 9004), and the wireless link monitoring means is disconnected from the wireless link. If the state is detected (procedure 9003), the packet relay means does not relay the received ACK packet to the wireless device. When the wireless link monitoring unit detects the connection state of the wireless link (procedure 9005), the ACK packet storage unit replicates one or more (n) ACK packets stored last in the TCP session (procedure 9006). The relay means transmits all the copied ACK packets to the wireless device (procedure 9007).

  In the procedure 9006, the TCP implemented in the ground terminal 1 and the mobile terminal 41 that are transmission / reception terminals include the Fast Retransmit and Fast Recovery functions described in RFC2581 and the like. In consideration of the case, in order to send three or more duplicated ACK packets to the transmitting terminal, three or more duplicated ACK packets may be duplicated.

  An example of a packet transmission / reception flow in the present embodiment is shown in FIG. The flow shown in FIG. 4 is common to the ground side and the mobile side. When the ground terminal 1 is a transmission terminal, the transmission terminal 91 transmits the ground terminal 1, the transmission side relay device 92 transmits the ground station relay device 30, and the transmission. The side radio device 93 means the ground station radio device 31, the reception side radio device 94 means the mobile station radio device 431, the reception side relay device 95 means the mobile station relay device 430, and the reception terminal 96 means the mobile terminal 41.

  On the other hand, when the mobile terminal 41 is a transmission terminal, the transmission terminal 91 receives the mobile terminal 41, the transmission side relay device 92 receives the mobile station relay device 430, the transmission side radio 93 receives the mobile station radio 431, The side radio device 94 means the ground station radio device 31, the reception side relay device 95 means the ground station relay device 30, and the reception terminal 96 means the ground terminal 1.

  As shown in FIG. 4, the transmission terminal 91 transmits data packets 1 to 4 and the reception terminal 96 receives them. The receiving terminal 96 transmits ACK packets 1 to 4 as confirmation responses to the data packets 1 to 4, and the transmitting terminal 91 receives them. At this time, the receiving side relay device 95 accumulates the latest ACK packet to be relayed, and therefore accumulates the ACK packet 4 when the ACK packet 4 is received.

  Immediately after that, it is assumed that a handover occurs and data packets 5 to 8 transmitted from the transmission terminal 91 are lost. During handover, the radio link is disconnected. However, when the handover is completed and the radio link connection state is restored, and the reception side radio 94 confirms the radio link recovery, the reception side relay device 95 has accumulated. A plurality of received ACK packets 4 are transmitted to the transmitting terminal 91 side. By receiving the ACK packet 4, the transmission terminal 91 determines that the data packet 5 and later have been lost, and retransmits the data packets 5 to 8.

  When receiving terminal 96 receives data packets 5-8, ACK packets 5-8 are transmitted as confirmation responses to data packets 5-8, and transmitting terminal 91 receives them. The transmission terminal 91 receives the ACK packets 5 to 8 and determines that there is no loss of the data packet, transmits the data packets 9 to 12, and thereafter repeats this operation.

  FIG. 5 is a diagram for explaining the effect of the present embodiment. The graph shown in FIG. 5 represents the relationship between the accumulated transfer data amount (vertical axis) and the elapsed time (horizontal axis) from the start of data transfer by TCP.

  A graph 700 shows a change in the amount of transfer data until a handover occurs, and so far is equivalent to the conventional technique determined by RTT. When a handover occurs, in the conventional technique, a packet cannot be transmitted until the retransmission timeout period elapses. Therefore, retransmission starts from the time when a retransmission notification period to the transmission terminal is added. The amount changes.

  On the other hand, in the present embodiment, as described above, by receiving the ACK packet 4, it is determined that the data packet 5 and later are lost, and the data packets 5 to 8 are retransmitted. Since retransmission is started from the point of adding a retransmission notification period to the terminal, the amount of transfer data changes as shown in a graph 702.

  Thus, even if it is assumed that the packet retransmission notification period to the transmitting terminal required after the handover period ends is equal to that in the prior art, if the retransmission start time is early as in this embodiment, the total time required for data transfer The communication throughput, which is defined by the amount of transfer data divided by the total time required for data transfer, is improved. Also, the use efficiency of the wireless transmission path is improved by shortening the period during which no packet flows.

  Thus, according to this embodiment, when the radio link recovers from the non-connected state to the connected state after the handover, the transmitting terminal does not wait for the retransmission timeout time of the transmitting terminal or the estimated retransmission timeout time at the receiving terminal. The loss of the data packet can be detected, the data packet can be retransmitted at an early stage, the use efficiency of the wireless transmission path can be improved in the TCP communication in the mobile communication, and the communication throughput can be improved.

  In the first embodiment, the case of one TCP session has been described. However, one terminal establishes different sessions simultaneously with a plurality of terminals to perform TCP communication, or a plurality of applications between a pair of transmission / reception terminals. However, TCP communication may be performed by simultaneously establishing different sessions, or by establishing sessions in parallel between a plurality of pairs of transmission / reception terminals.

  When multiple sessions with different requests for data transfer time and communication throughput coexist, priority is given to the session to be relayed, and when the communication is restored after handover, packet retransmission is started first from the session with higher priority Sometimes it is better.

  In the second embodiment, in the ground station relay device 30 and the mobile station relay device 430, priorities are set in advance with respect to the determination items for each session, and the wireless link monitoring unit changes the wireless link from the disconnected state to the connected state. When the change is detected, the ACK packet storage means copies one or more (n) ACK packets stored last in each TCP session based on a preset priority, and the packet relay means The transmitted ACK packet is transmitted to the wireless device.

  The priorities set in advance are stored in the ACK packet accumulating unit, and an example of the setting table is shown in FIG. As shown in FIG. 6, in the setting table 801, necessity of ACK accumulation and ACK transmission priority are set for each determination item.

  Here, the determination items include, for example, an application, a port number, an address, and a provider.

  When an application is a determination item, the application includes, for example, WWW (World Wide Web), SMTP (Simple Mail Transfer Protocol), POP (Post Office Protocol), FTP (File Transfer Protocol), and the like in the TCP header of the packet Is identified by the destination port number or the source port number described in.

  In addition to these applications, there are applications that perform TCP communication by specifying a special port number. This application is also identified by the destination port number or source port number described in the TCP header of the packet. The

  When a specific address such as an IP (Internet Protocol) address or a MAC (Media Access Control) address is used as a determination item, a destination IP address, a transmission source IP address, and a MAC described in the IP header of the packet are used. It is identified by the destination MAC address or source MAC address described in the header.

  When the provider is a determination item, the provider is identified by an IP address in the IP header of the packet or a VLAN (Virtual LAN) identifier in the MAC header.

  The setting table 801 sets whether or not ACK accumulation is required for each determination item, and sets a priority order for the determination items that require ACK accumulation. Note that it is not necessary to set a priority for a determination item that does not require ACK accumulation, and the priority is set to 0 in the example shown in FIG.

  The operation procedure in the ground station relay device 30 and the mobile station relay device 430 will be described with reference to FIG. In FIG. 7, as in FIG. 3, in the operation of the ground station relay device 30, “transmission path” means the terrestrial data transmission path 2, “radio unit” means the ground station radio unit 31, and mobile station relay In the operation of the device 430, “transmission path” means the mobile data transmission path 42, and “radio unit” means the mobile station radio unit 431.

  When the packet relay means receives the ACK packet from the transmission path (procedure 9021), the ACK packet accumulation means accumulates the received ACK packet for each TCP session in each TCP session for which priority is set (procedure 9022), and wirelessly. If the link monitoring means detects that the wireless link is connected (procedure 9023), the packet relay means relays the received ACK packet to the wireless device (procedure 9024). If the wireless link monitoring means detects that the wireless link is not connected (step 9023), the packet relay means does not relay the received ACK packet to the wireless device, and the wireless link monitoring means connects to the wireless link. When the status is detected, the ACK packet storage means replicates one or more (n) ACK packets stored last in each TCP session in the order of the set priority (step 9026), and the packet relay means The transmitted ACK packet is transmitted to the wireless device (procedure 9027).

  In the procedure 9026, considering the case where the TCP implemented in the transmission / reception terminal includes the Fast Retransmit and Fast Recovery functions described in RFC2581, etc., three In order to send the above duplicated ACK packet to the transmitting terminal, three or more may be duplicated.

  An example of a packet transmission / reception flow in this embodiment is shown in FIG. In the example illustrated in FIG. 8, it is assumed that the determination item is an application, and the applications A to D of the transmission terminal perform TCP communication with the applications A to D of the reception terminal, respectively. Therefore, the determination items of the setting table 801 are each application, and a priority order is set for each application.

  In FIG. 8, as in FIG. 4, when the ground terminal is a transmission terminal, the transmission terminal 91 is the ground terminal 1, the transmission side relay device 92 is the ground station relay device 30, and the transmission side radio 93 is the ground station radio 31. The reception side radio 94 means the mobile station radio 431, the reception side relay device 95 means the mobile station relay device 430, the reception terminal 96 means the mobile terminal 41, and when the mobile terminal is the transmission terminal, the transmission is performed. The terminal 91 is the mobile terminal 41, the transmission side relay device 92 is the mobile station relay device 430, the transmission side radio 93 is the mobile station radio 431, the reception side radio 94 is the ground station radio 31 and the reception side. The relay device 95 means the ground station relay device 30, and the receiving terminal 96 means the ground terminal 1.

  As shown in FIG. 8, the transmission terminal 91 transmits data packets A1 to D1 of applications A to D, and the reception terminal 96 receives them. The receiving terminal 96 transmits ACK packets A1 to D1 as confirmation responses to the data packets A1 to D1, and the transmitting terminal 91 receives them. Here, in the setting table 801, as shown in FIG. 6, the applications A, B, and C require ACK accumulation, the ACK transmission priorities are set to 2, 3, and 1, respectively, and the application D accumulates ACK. Is set to be unnecessary.

  At this time, the receiving-side relay device 95 stores the latest ACK packets A1, B1, and C1 of the applications A, B, and C, which are determination items for which priority is set in the setting table 801 among the ACK packets to be relayed. ing.

  Immediately after that, it is assumed that a handover occurs and the data packets A2 to D2 transmitted from the transmission terminal 91 are lost. During handover, the radio link is disconnected. However, when the handover is completed and the radio link connection state is restored, and the receiving radio 94 confirms the radio link recovery, A plurality of ACK packets C1, A1, and B1 are transmitted to the transmitting terminal side in the order of the applications C, A, and B having the highest priority. The transmission terminal 91 receives the ACK packets C1, A1, and B1, thereby determining that the data packet has been lost, and retransmits the data packets C2, A2, and B2 in this order.

  Note that since the priority is not set in the setting table 801, the application D does not perform the processing such as the applications A, B, and C, and performs packet retransmission by a retransmission timeout which is a conventional TCP retransmission procedure.

  As described above, according to the present embodiment, when the radio link recovers from the non-connected state to the connected state after the handover occurs, the transmitting terminal can detect the loss of the data packet according to the set priority, and the data can be detected early. Packets can be resent.

  In the first and second embodiments, immediately after detecting that the radio link is restored from the non-connected state to the connected state after the handover occurs, the latest information accumulated from the receiving-side radio 94 to the transmitting terminal 91 is stored. By transmitting the ACK packet, the packet retransmission timing from the transmission terminal 91 was accelerated.

  In the third embodiment, a method for further accelerating the packet retransmission timing from the transmission terminal 91 will be described.

  The configuration example of the mobile communication system is the same as in the first and second embodiments, but the ground station relay device 30 includes a packet relay unit that relays the packet received from the ground station radio 31 to the ground terminal 1, Data packet storage means for storing a plurality of latest data packets of TCP communication relayed from the ground terminal 1 to the ground station radio 31, and a radio link between the ground station radio 31 and the mobile station radio 431 Radio link monitoring means for constantly monitoring the connection state is included.

  The mobile station relay device 430 includes a packet relay unit that relays the packet received from the mobile station radio 431 to the mobile terminal 41 and the latest plurality of TCP communications that relay from the mobile terminal 41 side to the mobile station radio 431. Data packet storage means for storing the data packet, and wireless link monitoring means for constantly monitoring the connection state of the wireless link between the mobile station radio 431 and the ground station radio 31.

  The radio link monitoring means and the method for detecting the connection state of the radio link are the same as those in the first and second embodiments. In this embodiment, the software is implemented on the computer as in the first embodiment. A case will be described as an example. The terrestrial data transmission path 2, the mobile data transmission path 42, the ground station radio 31 and the mobile station radio 431 are the same as those in the first and second embodiments.

  The operation procedure in the ground station relay device 30 and the mobile station relay device 430 of this embodiment will be described with reference to FIG.

  In the operation procedure shown in FIG. 7, if the operation of the ground station relay device 30, “transmission path” means the terrestrial data transmission path 2, “radio device” means the ground station radio device 31, and the mobile station relay device 430. In this operation, “transmission path” means the mobile data transmission path 42, and “radio unit” means the mobile station radio unit 431.

  When the packet relay means receives a data packet from the transmission path (procedure 9041), the data packet storage means accumulates the received data packet for each TCP session (procedure 9042), and the wireless link monitoring means indicates that the wireless link is in a connected state. If detected (procedure 9043), the packet relay means relays the received data packet to the radio (procedure 9044), and if the radio link monitoring means detects that the radio link is disconnected (procedure 9043). The packet relay means does not relay the received data packet to the wireless device. When the wireless link monitoring unit detects the connection state of the wireless link (procedure 9045), the packet relay unit transmits the latest plurality of data packets stored for each TCP session by the data packet storage unit to the wireless device. (Procedure 9046).

  In procedure 9046, the number of data packets transmitted by the packet relay means to the radio device may be three or more retroactively.

  An example of a packet transmission / reception flow in the present embodiment is shown in FIG.

  In FIG. 10, when the ground terminal is a transmission terminal, the transmission terminal 91 is the ground terminal 1, the transmission side relay device 92 is the ground station relay device 30, the transmission side radio 93 is the ground station radio 31 and the reception side radio. The device 94 means the mobile station radio 431, the receiving side relay device 95 means the mobile station relay device 430, the receiving terminal 96 means the mobile terminal 41, and when the mobile terminal is the transmitting terminal, the transmitting terminal 91 is the mobile body. The terminal 41, the transmission side relay device 92 is the mobile station relay device 430, the transmission side radio 93 is the mobile station radio 431, the reception side radio 94 is the ground station radio 31, and the reception side relay 95 is the ground The station relay device 30 and the receiving terminal 96 mean the ground terminal 1.

  In FIG. 10, the transmission terminal 91 transmits data packets 1 to 4 and the reception terminal 96 receives them. The receiving terminal 96 transmits ACK packets 1 to 4 as confirmation responses to the data packets 1 to 4, and the transmitting terminal 91 receives them.

  Immediately after that, a handover occurs, and it is assumed that the transmission-side relay device 92 receives data packets 5 to 8 from the transmission terminal 91 during the handover. At this time, the transmission side relay device 92 accumulates the latest plurality of data packets to be relayed, but in the example shown in FIG. , Data packets 6 to 8 are stored. However, the data packets 5 to 8 have not reached the receiving terminal 96.

  During handover, the radio link is disconnected. However, when the handover is completed and the radio link connection state is recovered, and the transmitting side relay device 92 confirms the recovery of the radio link, the accumulated data packets 6 to 8 are stored. Is sent to the receiving terminal.

  The receiving terminal 96 has received the data packets 6 to 8 but has received only up to the data packet 4 before that. Therefore, the receiving terminal 96 determines that the data packet 5 has been lost, and sends duplicate selective ACKs 6 to 8 to the transmitting terminal 91. Return to.

  Since the transmission terminal 91 receives a plurality of duplicate selective ACKs, the transmission terminal 91 detects that the data packet 5 has been lost, retransmits the data packet 5, and thereafter transmits the data packet 9 and subsequent data.

  In the present embodiment as well, as in the second embodiment, it is possible to set the priority order for the TCP session based on the determination items. In this case, the transmission side relay device according to the set priority order 92 may retransmit the data packet.

  As described above, in the present embodiment, since the data packet is accumulated as compared with the first and second embodiments in which the ACK packet is accumulated, the storage capacity of the storage device 603 is increased, but the wireless link is in the connected state. Since the data packet can be retransmitted after recovery, the data packet can be retransmitted at an early stage. In TCP communication in mobile communication, the utilization efficiency of the wireless transmission path can be improved and the communication throughput can be improved.

  In the description of the first to third embodiments so far, it is assumed that one of the transmission / reception terminals is the ground terminal 1, but it can be realized even when both of the transmission / reception terminals are mobile bodies 4. is there.

  That is, since there are a plurality of mobile bodies 4 shown in FIG. 1 and the mobile body 4 and the other mobile body 4 communicate with each other, in the description of the first to third embodiments, “ground terminal 1” is referred to as “the other Mobile terminal 41 ”,“ terrestrial data transmission path 2 ”as“ other mobile data transmission path 42 ”,“ ground station 3 ”as“ other mobile station 43 ”, and“ ground station relay device 30 ”as“ other Mobile station repeater 430 ”,“ ground station radio 31 ”as“ the other mobile station radio 431 ”, and“ ground station antenna 32 ”as“ the other mobile station antenna 432 ”.

  In the first and third embodiments, a method has been described in which packets are stored in either the receiving-side relay device or the transmitting-side relay device, and the stored packets are transmitted to the radio side after recovery of the radio link at the time of handover. However, a description will be given of a fourth embodiment in which the first and third embodiments are combined and the reception-side relay device and the transmission-side relay device are linked.

  The configuration example of the mobile communication system is the same as in the first to third embodiments, but the ground station relay device 30 includes a packet relay unit that relays the packet received from the ground station radio 31 to the ground terminal 1. Data packet storage means for storing the latest plurality of data packets of the TCP communication relayed from the ground terminal 1 side to the ground station radio 31 and the latest of the TCP communication relayed from the ground terminal 1 side to the ground station radio 31 ACK packet accumulating means for accumulating ACK packets, and radio link monitoring means for constantly monitoring the connection state of the radio link between the ground station radio 31 and the mobile station radio 431.

  The mobile station relay device 430 includes a packet relay unit that relays the packet received from the mobile station radio 431 to the mobile terminal 41 and the latest plurality of TCP communications that relay from the mobile terminal 41 side to the mobile station radio 431. Data packet storing means for storing the data packet, ACK packet storing means for storing the latest ACK packet of TCP communication relayed from the mobile terminal 41 side to the mobile station radio 431, the mobile station radio 431 and the ground station The radio link monitoring means for constantly monitoring the connection state of the radio link with the radio 31 is configured.

  The wireless link monitoring means and the method for detecting the connection state of the wireless link are the same as those in the first to third embodiments. In this embodiment, the software is implemented on the computer as in the first embodiment. A case will be described as an example. The terrestrial data transmission path 2, the mobile data transmission path 42, the ground station radio 31 and the mobile station radio 431 are the same as those in the first and second embodiments.

  Operation procedures in the ground station relay device 30 and the mobile station relay device 430 will be described with reference to FIGS.

  In the operation procedure shown in FIG. 11 and FIG. 12, if the operation of the ground station relay device 30, the “transmission path” means the terrestrial data transmission path 2, the “radio device” means the ground station radio device 31, and the mobile station In the operation of the relay device 430, “transmission path” means the mobile data transmission path 42 and “radio device” means the mobile station radio 431.

  First, the operation procedure of the receiving side relay apparatus will be described with reference to FIG.

  When the packet relay means receives a data packet from the wireless device (procedure 9061), it transmits the received data packet to the transmission path (procedure 9062), and when the packet relay means receives an ACK packet from the transmission path (procedure 9063), The ACK packet accumulating unit accumulates the received ACK packet (procedure 9064), and if the radio link monitoring unit detects that the radio link is connected (procedure 9065), the packet relay unit transmits the received ACK packet. When relaying to the radio (procedure 9066) and the radio link monitoring means detects that the radio link is disconnected (procedure 9065), the packet relay means does not relay the received ACK packet to the radio, and the radio link When the monitoring means detects that the wireless link is connected (procedure 9067), the ACK packet storage means Packet relay means an ACK packet products are transmitted to the radio (Step 9068).

  Note that the operation procedure from the procedure 9064 to the procedure 9068 is performed independently for each TCP session.

  Next, the operation procedure of the transmission side relay apparatus will be described with reference to FIG.

  When the packet relay means receives an ACK packet from the wireless device (procedure 9071), it transmits the received ACK packet to the transmission path (procedure 9072), and when the packet relay means receives a data packet from the transmission path (procedure 9073), data The packet accumulating unit accumulates the received data packet (procedure 9074), and if the radio link monitoring unit detects that the radio link is in a connected state (procedure 9075), the packet relay unit wirelessly receives the received data packet. If the wireless link monitoring means detects that the wireless link is disconnected (procedure 9075), the packet relay means does not relay the received data packet to the wireless equipment, and the wireless link monitoring means When the means detects that the wireless link is connected (step 9077), it receives an ACK packet from the wireless device. Chi (Step 9078), when receiving the ACK packet from the wireless device, and transmits all the stored data packets having a value more than the sequence number of the sequence number of the received ACK packet to the radio (Step 9079).

  Note that the operation procedure from step 9074 to step 9079 is performed independently for each TCP session.

  An example of a packet transmission / reception flow in this embodiment will be described with reference to FIG.

  In the flow shown in FIG. 13, when the ground terminal is the transmission terminal, the transmission terminal 91 is the ground terminal 1, the transmission side relay device 92 is the ground station relay device 30, and the transmission side radio 93 is the ground station radio 31. The reception side radio 94 means the mobile station radio 431, the reception side relay device 95 means the mobile station relay device 430, the reception terminal 96 means the mobile terminal 41, and when the mobile terminal is the transmission terminal, the transmission is performed. The terminal 91 is the mobile terminal 41, the transmission side relay device 92 is the mobile station relay device 430, the transmission side radio 93 is the mobile station radio 431, the reception side radio 94 is the ground station radio 31 and the reception side. The relay device 95 means the ground station relay device 30, and the receiving terminal 96 means the ground terminal 1.

  As shown in FIG. 13, the transmission terminal 91 transmits data packets 1 to 4 and the reception terminal 96 receives them. The receiving terminal 96 transmits ACK packets 1 to 4 as acknowledgments for the data packets 1 to 4, but then a handover occurs, the transmitting terminal 91 receives the ACK packets 1 and 2, and the ACK packets 3 and 4 are lost. Suppose that it did not reach the transmission terminal 91.

  At this time, the receiving side relay device 95 accumulates the latest ACK packet to be relayed, and therefore accumulates the ACK packet 4 when the ACK packet 4 is received.

  Further, it is assumed that data packets 5 and 6 are transmitted from the transmission terminal 91, but the data packets 5 and 6 are lost due to occurrence of handover.

  At this time, the receiving side relay device 95 stores a plurality of the latest data packets to be relayed. However, if five data packets are stored in the example of FIG. 6 has been accumulated.

  During handover, the radio link is disconnected. However, when the handover is completed and the radio link is restored to the connected state, and the receiving radio 94 confirms the recovery of the radio link, the accumulated ACK packet 4 is received. To the side radio 94.

  The transmission-side relay device 92 receives the ACK packet 4, determines that the data packet 5 and the subsequent data are lost, and transmits the stored data packets 5 and 6 to the transmission-side radio 93.

  The receiving terminal 96 receives the data packets 5 and 6, transmits ACK packets 5 and 6 to them, and the transmitting terminal 91 receives them.

  The transmission terminal 91 receives the ACK packets 5 and 6 and determines that the data packet 6 has arrived at the reception terminal side.

  The transmission terminal retransmits the data packets 3 to 6 according to the present embodiment shown in FIG. 13, the elapsed time from the transmission terminal 91 transmitting the data packet 3 to receiving the ACK packet 6 is less than the retransmission timeout period. If so, the transmission terminal 91 can continuously transmit data without causing retransmission processing. If retransmission processing does not occur, generation of useless retransmission packets can be suppressed, and slow start and congestion avoidance at the time of packet retransmission are not required, so that a decrease in transmission speed (communication throughput) after data packet 7 can be prevented.

  Further, as in the case shown in FIG. 5, it is possible to improve communication throughput and use efficiency of a wireless transmission path.

  Also in the present embodiment, as in the second embodiment, it is possible to set the priority order for the TCP session based on the determination items. In this case, the receiving side relay is performed in the order according to the set priority order. The device 95 may transmit the ACK packet to the reception-side radio 94 side, and the transmission-side relay device 92 may transmit the data packet to the transmission-side radio 93 side in the order according to the set priority.

  As described in the fourth embodiment, the case where one of the transmission / reception terminals is the ground terminal 1 has been described in the present embodiment, but the same can be realized even when both of the transmission / reception terminals are mobile units 4. .

1 is a configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a block diagram of the relay apparatus which concerns on this embodiment. It is a figure which shows the operation | movement procedure of the relay apparatus which concerns on this embodiment. It is a figure which shows the example of the relay flow of the packet which concerns on this embodiment. It is a figure explaining the shortening effect of the data transfer time which concerns on this embodiment. It is a figure which shows the priority setting table which concerns on 2 embodiment of this invention. It is a figure which shows the operation | movement procedure of the relay apparatus which concerns on this embodiment. It is a figure which shows the example of the relay flow of the packet which concerns on this embodiment. It is a figure which shows the operation | movement procedure of the relay apparatus which concerns on 3rd Embodiment of this invention. It is a figure which shows the example of the relay flow of the packet which concerns on this embodiment. It is a figure which shows the operation | movement procedure of the relay apparatus which concerns on 4th Embodiment of this invention. It is a figure which shows the operation | movement procedure of the relay apparatus which concerns on this embodiment. It is a figure which shows the example of the relay flow of the packet which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground terminal 2 Ground data transmission path 3 Ground station 4 Mobile body 30 Ground station relay apparatus 31 Ground station radio | wireless machine 32 Ground station antenna 41 Mobile terminal 42 Mobile body data transmission path 43 Mobile station 91 Transmission terminal 92 Transmission side relay apparatus 93 Transmission side radio 94 Reception side radio 95 Reception side relay device 96 Reception terminal 430 Mobile station relay device 431 Mobile station radio 432 Mobile station antenna 600 Computing device 601 Input device 602 Output device 603 Storage device 604 External interface device 801 Setting table

Claims (9)

And radio equipment is connected to a plurality of terminals including the mobile terminal and the ground terminal, a mobile communication system for transmitting and receiving packets between the ground terminal and the mobile terminal via a radio transmission path ,
A mobile-side relay device connected to the mobile terminal via a data transmission path, and a ground-terminal relay device connected to the ground terminal via a data transmission path, respectively,
A packet relay means for relaying a packet received from the terminal of the communication partner via the wireless device to the terminal connected to its own relay device, and relaying an acknowledgment packet for the communication partner to the wireless device;
Acknowledgment packet accumulation means for sequentially accumulating the acknowledgment packet created every time a packet is received from the communication partner terminal ;
Wherein the connection state of the radio link of the radio transmission path, is configured to include a, a radio link monitoring means for monitoring and exchanging data between the relay apparatus and the ground terminal side of the relay device of the moving body side,
When the wireless link monitoring means detects that the connection state of the wireless link has returned from non-connected to the connected state, the latest confirmation response packet among the confirmation response packets stored in the confirmation response packet storage means is transmitted to the wireless transmission path. The mobile communication system , wherein the communication partner terminal that has received the latest acknowledgment packet determines a data packet to be transmitted including a data packet to be retransmitted based on the received acknowledgment packet. A mobile communication system in which a wireless device is connected to each of a plurality of terminals, and packets are transmitted and received between the plurality of terminals via a wireless transmission path,
Each of the plurality of terminals includes a relay device connected by a data transmission path,
The relay device provided in each of the plurality of terminals,
A packet received from the communication partner terminal via the wireless device among the plurality of terminals is relayed to the terminal connected to the own relay device, and an acknowledgment packet for the communication partner terminal is relayed to the wireless device and a packet relay means that,
Each time the acknowledgment packet is created by receiving a packet from the communication partner terminal, an acknowledgment packet accumulating unit that sequentially updates and accumulates the newly created acknowledgment packet;
The wireless link connection state of the wireless transmission path is configured to include wireless link monitoring means for exchanging data and monitoring between the mobile unit side relay device and the ground terminal side relay device ,
Wherein the radio link monitoring means is connected state of the wireless link is detected that it has returned to connect disconnected, it transmits the acknowledgment packets stored in said acknowledgment packet storage means to the radio transmission path, the communication partner The mobile communication system determines a data packet to be transmitted including a data packet to be retransmitted based on the received acknowledgment packet. The mobile communication system according to claim 1 or 2, wherein a plurality of the acknowledgment packets are duplicated and transmitted to the wireless transmission path. The acknowledgment packet accumulating unit accumulates the acknowledgment packet for each of a plurality of different sessions, and the accumulated latest acknowledgment packet is stored for each session in the order of priority set for each session. The mobile communication system according to claim 1, wherein the mobile communication system transmits to a transmission line. The relay device has data packet storage means for storing a plurality of latest data packets relayed from a terminal to a radio device, and has a sequence number equal to or greater than the sequence number value of the received acknowledgment packet The mobile communication system according to claim 1 or 2, wherein a packet is transmitted to the wireless device. The data packet storage means stores data packets for a plurality of different sessions, and stores the latest data packets stored in the wireless transmission path for each session in a priority order set for each session. The mobile communication system according to claim 5 for transmission. A radio is connected to each of a plurality of terminals including a mobile terminal and a ground terminal,
Wherein the relay apparatus connected to the movable body side to the mobile terminal in a data transmission path, and the ground terminal are connected by data transmission line are terrestrial terminal repeater, respectively,
A packet relay means for relaying a packet received from the terminal of the communication partner via the wireless device to the terminal connected to its own relay device, and relaying an acknowledgment packet for the communication partner to the wireless device;
Acknowledgment packet accumulating means for sequentially accumulating the acknowledgment packet created each time a packet is received from the communication partner terminal ;
Wherein the connection state of the radio link of the radio transmission path, is configured to include a, a radio link monitoring means for monitoring and exchanging data between the relay apparatus and the ground terminal side of the relay device of the moving body side,
The radio link when the monitoring means is connected state of the wireless link is detected that it has returned to connect disconnected, the wireless transmission channel the latest acknowledgment packet of the acknowledgment packets stored in said acknowledgment packet accumulating means transmitted to the terminal of the latest acknowledgment packet has been received the communications partner, the data packet to be transmitted, including the data packet to be retransmitted is determined based on the received acknowledgment packet, the data packets the determined A mobile communication method for transmitting and receiving packets between a mobile terminal and a ground terminal via the wireless transmission path.   The acknowledgment packet accumulating unit accumulates the acknowledgment packet for each of a plurality of different sessions, and the accumulated latest acknowledgment packet is stored for each session in the order of priority set for each session. The mobile communication method according to claim 7, wherein the mobile communication method is transmitted to a transmission path.   The acknowledgment packet is accumulated for a plurality of different sessions, the data packet is accumulated for a plurality of different sessions, and the accumulated latest acknowledgment packet is stored for each session in an order based on the set priority of the sessions. The mobile communication method according to claim 7, wherein the mobile communication method transmits to the wireless transmission path and transmits the accumulated data packet to the wireless transmission path for each session.

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