JP4348168B2 - COMMUNICATION DEVICE, TRANSMITTER, COMMUNICATION SYSTEM, COMMUNICATION METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to a communication control technique in a data link layer and a transport layer.

  One of the data link layer communication protocols in the OSI hierarchical model is the RLC (Radio Link Control) protocol standardized for radio link control. The RLC protocol is proposed in 3GPP (3rd Generation Partnership Project) as shown in Non-Patent Document 1, and the RLC protocol includes an upper-side of the two sublayers constituting the data link layer. An operation (communication process) performed by the communication node in the RLC sublayer is defined.

  The operation modes in the RLC sublayer include AM (Acknowledgement Mode), UM (Unacknowledgement Mode), and TM (Transparent Mode), and the operation mode is a transmission node that performs a transmission operation in the RLC sublayer of the AM. The only receiving nodes that can transfer data are the receiving nodes that perform the receiving operation in the RLC sublayer whose operation mode is AM. Of the operation modes in the RLC sublayer, only the AM is related to the problem to be solved by the present invention. Therefore, the operation mode will be described below with a focus on the RLC sublayer in which the operation mode is AM. In the following description, “RLC sublayer” means an RLC sublayer whose operation mode is AM.

  In the RLC sublayer, the data transfer between the transmission node and the reception node is performed on the header of partial data cut out in order from the beginning of the data unit (hereinafter referred to as SDU (Service Data Unit)) passed between the upper layer and the lower layer. Is performed using a data unit (hereinafter referred to as PDU (Protocol Data Unit)) generated by adding. The header of the PDU includes a sequence number indicating the order in which the PDU is generated and length information of the cut-out SDU. In the RLC sublayer, PDUs lost in data transfer are retransmitted by selective retransmission using a sequence number. In the following description, “SDU” and “PDU” mean SDUs and PDUs in the RLC sublayer.

  By the way, the wireless link has a higher error rate in data transfer than the wired communication link. For this reason, the retransmitted PDU is likely to disappear again. That is, the retransmission delay is large. Therefore, in the RLC sublayer, not only the PDU, but also the SDU reception order (strictly, the PDU necessary for assembling the SDU can be switched after the end of the delivery from the MAC (Medium Access Control) sublayer). There is. In order to absorb the influence of the change of the reception order of the SDUs in the RLC sublayer whose retransmission cost is lower than that of the upper layer, the receiving node controls the order of the SDUs in the RLC sublayer. Specifically, when the receiving order of the SDUs is switched and an SDU that should be passed to an upper layer after an unreceived SDU is received first, the receiving node receives the SDU that has not been received and receives the SDU. Hold until passed to. Such order control ensures that SDUs are passed from the RLC sublayer to the upper layer at the receiving node in the order that the SDU is passed from the upper layer at the transmitting node. In order to detect a change in the reception order of the SDUs, the receiving node needs to grasp the order in which the SDUs are passed from the upper layer to the RLC sublayer at the transmission node. This grasp can be realized by using the sequence number and length information included in the header of the PDU.

  However, the delay of the SDU due to such sequence control causes a substantial decrease in the utilization rate of the communication network. Note that the “utilization rate of the communication network” is the network resource capacity actually used for the capacity of the network resource provided by the communication network (for example, the bandwidth of the available communication link and the period during which the communication link can be used). The “substantial utilization rate of the communication network” means the ratio of the amount of network resources used effectively to the capacity of the network resources provided by the communication network. The reason that the delay of the SDU in the RLC sublayer causes a substantial decrease in the utilization rate of the communication network is different depending on the type of data transfer performed in the transport layer, and will be described separately.

[For bulk data transfer]
In bulk data transfer, generally, flow control is performed in an upper layer to adjust the amount of data staying in the communication network and to keep the communication network usage rate appropriate. An example of such flow control is congestion control in TCP (Transmission Control Protocol). The above flow control is performed based on the data unit passed from the lower layer in the transport layer. Therefore, if a layer that can be passed to the upper layer after delaying a data unit that can be passed to the upper layer, such as the RLC sublayer, is present in the lower layer of the transport layer, the above flow control starts. There is a risk of delay. In flow control, data for control is sent from the node to the communication network, so the delay in the start of flow control leads to a reduction in data staying in the communication network. Specifically, there are phenomena such as an increase in retransmission notification delay, an increase in congestion notification delay, bursty data transmission, and delay in data reception of other sessions. The above is the reason why the substantial utilization rate of the communication network is reduced. Note that TCP stipulates that data is correctly arranged and then passed to an upper layer, and there is a problem that the order control has duplicated functions in the transport layer and the data link layer.

[For streaming transfer]
In streaming transfer, data delay is generally limited. Therefore, when there is a layer that can be passed to the upper layer after delaying a data unit that can be passed to the upper layer, such as the RLC sublayer, the transport layer receives the data at the lower layer. The node is more likely to receive data units that are no longer useful. Since such a data unit is discarded and is not used, the network resource used for transferring such a data unit is wasted. This is the reason why the substantial utilization rate of the communication network is reduced.

  In order to avoid such inconvenience, it is conceivable not to perform SDU order control in the RLC sublayer. In this way, a substantial reduction in the utilization rate of the communication network due to the SDU delay in the RLC sublayer does not occur. However, in the transport layer, replacement of SDUs may be erroneously detected as SDU loss, and improper flow control may be performed. By the way, technologies for preventing inappropriate flow control are described in Patent Document 1 and Patent Document 2.

  In the technique described in Patent Document 1, the transmitting node can detect a data unit (erasure is detected) using the TCP SACK (Selective Acknowledgment) option only when the size of the congestion window is equal to or smaller than a predetermined threshold. Data unit) immediately. In other words, the transmitting node operates according to the notification using the SACK option only when a serious inconvenience may occur if the SACK option is not used. According to this technology, the frequency of occurrence of false detections is lower when compared with a mode in which notification by the SACK option is always trusted, but naturally increases when compared with a mode in which the SACK option is not used. Eventually, even if the technique described in Patent Document 1 is used, inappropriate flow control due to erroneous detection cannot be prevented.

In the technique described in Patent Document 2, when receiving a confirmation response after retransmission, the transmission node determines whether the confirmation response is for the original data unit or the retransmission data unit, and performs processing according to the determination result. Change. According to this technique, it seems that inappropriate flow control due to erroneous detection can be prevented. However, when the receiving node receives the third to fifth data units immediately after the first data unit, and then receives the second data unit, the transmitting node receives the second data unit. Missing data units are erroneously detected, and inappropriate flow control is performed. In the first place, the technique described in Patent Document 2 requires performing retransmission (a kind of flow control) that can later be found to be inappropriate, and cannot be a fundamental solution.
"3GPP specification: 25.322", [online], The 3rd Generation Partnership Project, [searched on August 29, 2003], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/ 25322.html> JP 2000-78195 A Special Table 2002-534907

  The present invention has been made under the above-mentioned background, and is caused by erroneously detecting the change of the reception order of the data units as the loss of the data units without reducing the substantial utilization rate of the communication network. An object of the present invention is to provide a technique capable of preventing inappropriate flow control.

The present invention is transmitted from the transmitter to the receiver, and a data receiving means for receiving data units of the transport layer has an identifiable number transmission order from the transmitter, said data unit by said data receiving means When received, in association with the number of the data unit, the data storage means for storing the data unit being transferred in the first storage means, and transmitting the data unit to the receiver; An acknowledgment receiving means for receiving an acknowledgment including a first number which is a number of a data unit which is transmitted from the receiver to the transmitter and is expected to be received next by the receiver; and the data receiving means When the data unit received and transmitted by the data transmission means is discarded, the data unit is associated with the number of the data unit. The overwriting means stored in the first storage means for overwriting that the data unit is being transferred and the confirmation response received by the confirmation response receiving means are stored in the first storage means. An acknowledgment transmission means for transmitting to the transmitter, wherein the acknowledgment transmission means is stored in the first number and the second storage means included in the confirmation response received by the confirmation response receiving means. When the second number of the data unit is compared and the second number is smaller than the first number, the first number is stored in the second storage means as the second number. Overwriting, overwriting the first storage means that a data unit with a number lower than the first number has been received by the receiver, and transferring the confirmation response to the transmitter; Is the number If the first storage means stores that the data unit of the first number is discarded when it is not younger than the number of 1, the confirmation response is forwarded to the transmitter, When it is stored that the data unit of the first number is being transferred, the confirmation response including information indicating that the data unit of the first number is being transferred is transmitted to the transmitter A communication device is provided.

Further, the present invention is estimated from the communication device according to any of the above, a receiving means for receiving the acknowledgment, the loss of the data unit based on the order or timing of reception of the data unit by receiver unit And when the confirmation response received by the reception means includes information indicating that the data unit of the first number included in the confirmation response is being transferred, There is provided a transmitter having prohibition means for temporarily prohibiting the loss estimation means from estimating the loss of a data unit.

The present invention also includes a transmitter and a communication device, wherein the transmitter transmits a transport layer data unit having a number that can specify a transmission order to a receiver, Erasure estimation means for estimating erasure of the data units based on the order or timing of reception of the data units by a receiver, and the communication device receives the data units transmitted from the transmitter. When the data unit is received by the first receiving means and the first receiving means, the first storage means stores the fact that the data unit is being transferred in association with the number of the data unit. Data transmitting means for transmitting the data unit to the receiver, and a data unit transmitted from the receiver to the transmitter and expected to be received next by the receiver. A confirmation response receiving means for receiving a confirmation response including a first number which is the number of a network, and when the data unit received by the first receiving means and transmitted by the data transmission means is discarded Is associated with the number of the data unit, and overwrite means stored in the first storage means for overwriting that the data unit is being transferred is stored in the first storage means, A confirmation response transmitting means for transmitting the confirmation response received by the confirmation response receiving means to the transmitter, wherein the confirmation response transmitting means of the communication device receives the confirmation response received by the confirmation response receiving means. And the second number of the data unit stored in the second storage means is compared, and the second number is smaller than the first number The first number is overwritten in the second storage means as the second number, and the data unit having a number lower than the first number has been received by the receiver. When the second number is not younger than the first number, the data unit of the first number is discarded. Is stored in the first storage means, the confirmation response is transferred to the transmitter, while when it is stored that the data unit of the first number is being transferred, said acknowledgment containing information data units 1 of number means that it is being transferred is transmitted to the transmitter, the transmitter further receives the transmitted said acknowledgment from said acknowledgment transmission means Second to And when the confirmation response received by the reception means includes information indicating that the data unit of the first number included in the confirmation response is being transferred. There is provided a communication system comprising: prohibiting means for temporarily prohibiting the disappearance estimating means from estimating the disappearance of a unit.

Further, the present invention provides a transmission process in which a transmitter transmits a data unit of a transport layer having a number that can specify a transmission order to a receiver, and a communication device transmits the data unit transmitted by the transmitter. The reception process, and the communication device stores in the first storage means that the data unit is being transferred in association with the received data unit number , and sends the data unit to the receiver. A data transmission process to be transmitted and an acknowledgment including a first number which is a number of a data unit transmitted from the receiver to the transmitter and expected to be received next by the receiver. An acknowledgment reception process to receive, and when the data unit received in the reception process and transmitted in the data transmission process is discarded by the communication device An overwriting process of overwriting that the data unit is being transferred, stored in the first storage means, in association with the number of the data unit, and the communication The apparatus compares the first number included in the confirmation response received in the confirmation response reception process with the second number of the data unit stored in the second storage means, and the second number When the number is lower than the first number, the first number is overwritten as the second number in the second storage means, and a data unit having a number lower than the first number is received by the receiver. Overwriting the first storage means that it has already been received at, transferring the confirmation response to the transmitter, and if the second number is not younger than the first number, Number 1 When the first storage means stores that the data unit is discarded, the confirmation response is transferred to the transmitter, while the fact that the data unit with the first number is being transferred is stored. And transmitting the acknowledgment response including information indicating that the data unit of the first number is being transferred to the transmitter, and the transmitter transmits the data by the receiver. An erasure estimation process for estimating the erasure of the data unit based on the reception order or timing of units; and the first response included in the confirmation response is included in the confirmation response transmitted by the transmitter in the confirmation response transmission process. case, the loss estimation process smell loss of the data units of the number of the data units contain information which means that it is being transferred And a canceling process for temporarily prohibiting estimation.

The present invention also provides a data receiving means for receiving a data unit of a transport layer transmitted from a transmitter to a receiver and having a number that can specify a transmission order from the transmitter, and the data receiving means. When the data unit is received, the first storage means stores the data unit being transferred in association with the number of the data unit, and transmits the data unit to the receiver. Transmitting means; and an acknowledgment receiving means for receiving an acknowledgment including a first number which is a number of a data unit which is transmitted from the receiver to the transmitter and is expected to be received next by the receiver; When the data unit received by the data receiving unit and transmitted by the data transmitting unit is discarded, the number of the data unit is discarded. Corresponding to the data unit, the fact that the data unit has been discarded is received by the overwriting means stored in the first storage means for overwriting that the data unit is being transferred, and the confirmation response receiving means. The first number included in the confirmation response is compared with the second number of the data unit stored in the second storage means, and the second number is smaller than the first number. In the case, the first number is overwritten as the second number in the second storage means, and the first data unit having a lower number than the first number has been received by the receiver. When the second number is not younger than the first number, the data unit of the first number is discarded. The first When it is stored in the storage means, the confirmation response is transferred to the transmitter, while when it is stored that the data unit of the first number is being transferred, the data unit of the first number Provides a program for causing an acknowledgment transmission means for transmitting the acknowledgment to the transmitter including information indicating that the message is being transferred .

  According to the present invention, the erasure estimation means temporarily cancels the estimation of the erasure of the data unit notified, thereby changing the reception order of the data units without reducing the substantial utilization rate of the communication network. Inappropriate flow control due to erroneous detection of data unit loss can be prevented. Therefore, according to the present invention, the substantial utilization rate of the communication network is improved.

[First Embodiment]
[Constitution]
FIG. 1 is a diagram showing a configuration of a communication system 100 according to the first embodiment of the present invention. As shown in this figure, a communication system 100 includes a mobile device 10 that is carried by a user, a base station 20 that can wirelessly communicate with the mobile device 10 in a wireless area under its control, and a core network to which the base station 20 is connected. 30 has a server device 40 connected thereto. The mobile device 10 can communicate with the server device 40 via the base station 20 and the core network 30. Note that the communication system 100 is compliant with IMT-2000 (International Mobile Telecommunications-2000), and the number of the mobile device 10, the base station 20, and the server device 40 is an arbitrary number of 1 or more.

  FIG. 2 is a diagram illustrating a communication protocol configuration of the communication system 100. As shown in this figure, communication in the layer above the transport layer is terminated only by the mobile device 10 and the server device 40, and communication in the layer below the network layer is terminated by all devices constituting the communication system 100. The However, the base station 20 operates the data unit of the transport layer with the snoop module. The base station 20 does not perform SDU order control in the RLC sublayer.

  The mobile device 10 and the server device 40 perform communication processing according to general TCP in the transport layer. The communication processing according to general TCP includes retransmission processing using a retransmission timer and fast retransmission (Fast Retransmission), and does not include processing using the SACK option. Hereinafter, retransmission processing using a retransmission timer and high-speed retransmission will be described.

  In TCP, data is cut out in order from the top of a data stream passed from a higher layer, and a header is attached to the cut out data to create a data segment. A sequence number indicating the cut-out position of the corresponding data is written in the header of the data segment. Hereinafter, unless otherwise specified, “sequence number” means a sequence number in TCP. When the transmitting node transmits the data segment thus created, the transmitting node starts a retransmission timer for the data segment. On the other hand, when receiving the data segment, the receiving node returns an acknowledgment segment indicating that fact. Upon receiving the acknowledgment segment, the transmitting node stops the retransmission timer that was started when transmitting the corresponding data segment, and avoids retransmission of the data segment due to retransmission timeout. By the way, the transmission node basically transmits the data segments in the order of the sequence numbers written in the header. For this reason, the receiving node determines the data segment with the smallest sequence number among the unreceived data segments as the data segment expected to be received next, and refers to the sequence number of the data segment (hereinafter referred to as “ACK value”). ) To the sending node using the above-mentioned acknowledgment segment. If an unexpected data segment is received despite this notification, the receiving node returns an acknowledgment segment having the same ACK value as the ACK value of the acknowledgment segment transmitted immediately before. This acknowledgment segment is called a duplicate acknowledgment segment. When the transmitting node continuously receives duplicate confirmation response segments by the number of retransmission thresholds, the transmission node regards that the data segment has been lost, and retransmits the data segment indicated by the duplicate confirmation response segment without waiting for a retransmission timeout. This is high-speed retransmission. In the present embodiment, the retransmission threshold is “3”.

  FIG. 3 is a block diagram showing the configuration of the base station 20. As is apparent from this figure, the base station 20 has a configuration in which the CPU 21 executes a program stored in the nonvolatile memory 22 by using the RAM 23 as a work area, and performs various processes, as in a general computer. It has become. In addition, the non-volatile memory 22 has a notification program 221 for performing notification processing described later, and performs communication processing in a layer lower than the transport layer, and uses the base station 20 as a relay device in the transport layer. A control program is stored that starts execution of the notification program 221 every time a communication connection is established and terminates execution of the replacement program when the communication connection is disconnected. The CPU 21 reads the control program from the nonvolatile memory 22 and executes it when a power supply (not shown) is turned on.

  The wireless unit 24 transmits / receives a wireless signal to / from the mobile device 10. When data to be transmitted is supplied from the CPU 21, the wireless unit 24 transmits a carrier wave modulated by the transmission data to the wireless section. When data is demodulated from the propagated carrier wave, the received data is supplied to the CPU 21. The wireless unit 24 and the CPU 21 transmit / receive data to / from the mobile device 10. The communication interface 25 transmits and receives signals to and from the core network 30. When data to be transmitted is supplied from the CPU 21, the signal modulated by the transmission data is transmitted to the core network 30. When the data is demodulated from the signal supplied from, the received data is supplied to the CPU 21. Data is transmitted to and received from the server device 40 via the core network 30 by the communication interface 25 and the CPU 21.

  The CPU 21 that is executing the control program detects when the transport layer communication connection is established with the base station 20 as a relay device, and reads the notification program 221 from the nonvolatile memory 22 and executes it. When the communication connection corresponding to the notification program 221 being executed is disconnected, the CPU 21 detects this and ends the execution of the notification program 221. The CPU 21 executing the notification program 221 performs notification processing described below for each communication connection in the transport layer in the snoop module.

  In the notification process, when the CPU 21 receives the data segment from the server device 40, the CPU 21 writes the status data indicating that the status of the received data segment is “transferring” to the status area 231 of the RAM 23, while moving the data segment. Transfer to machine 10. In the notification process, if the CPU 21 discards the data segment in the lower layer (specifically, the RLC sublayer), the snoop module displays the discard fact and the sequence number of the discarded data segment. A discard notification is obtained from the lower layer, and the status data of the data segment written in the status area 231 is overwritten with the status data indicating that the status of the data segment is “discard”.

  In the notification process, when receiving the confirmation response segment from the mobile device 10, the CPU 21 compares the sequence number written in the duplication determination area 232 of the RAM 23 with the ACK value of the confirmation response segment, and the former is greater than the latter. If it is young, the process of overwriting the latter in the duplication determination area 232, the process of transmitting the confirmation response segment to the server device 40, and the state of the data segment confirmed to be received by the confirmation response segment is “Received”. The status data of the relevant data segment written in the status area 231 is overwritten with the status data indicating this.

  When the former is not younger than the latter, the CPU 21 determines whether or not the state of the data segment whose sequence number is the ACK value of the confirmation response segment is “transferring”, and must be “transferring”. Then, the confirmation response segment is transferred to the server device 40 as it is. In addition to “discarding” and “reception”, a state in which the core network 30 is congested or the like is discarded before reaching the base station 20 can be considered as a state that is not “transferring”. On the contrary, if it is “transferring”, the CPU 21 sets the EON bit of the confirmation response segment to ON, and transmits the confirmation response segment after setting to the server device 40. That is, the CPU 21 sets the EON bit to ON only when the received acknowledgment segment is a duplicate acknowledgment segment and a data segment having the ACK value of the acknowledgment segment as a sequence number has been received. The confirmation response segment is transmitted to the server device 40. In other words, when the CPU 21 detects that the order of the data segments has been changed by the reception of the data segments in the mobile device 10, the data received by the mobile device 10 with the order changed at the time of detection. It is determined whether or not the segment has been received. Only when the segment has been received, the server device 40 is notified that the data segment is a replacement segment. Note that the EON bit is one bit in an unused area of a data segment in general TCP, and is set to off by default, and is not used in communication according to general TCP.

  The replacement segment means that the mobile device 10 first receives the data segment to be received first, next receives the data segment to be received fourth, and then receives the second data segment. When a data segment is received, it refers to the data segment to be received second. As is clear from the above, in this embodiment, even if a data segment whose sequence number is the ACK value of the duplication confirmation response segment is a replacement segment, the fact that the data segment is a replacement segment is notified to the server device 40. Not always notified. This is because a condition that the state of the data segment is “transferring” is added as a condition for this notification. This condition may be changed so that the server device 40 is always notified if it is a replacement segment. However, even if such a change is made, the substantial utilization rate of the communication network does not improve, and the data segment The possibility of erroneously detecting the change of the receiving order as the loss of the data segment is not lowered. Therefore, in this embodiment, a simple condition that the state of the data segment is “in transfer” is adopted.

  In addition, in this embodiment, the notification destination of the replacement segment in the notification process is that the loss of the data segment is estimated based on the order or timing of reception of the data segment by the mobile device 10, and the estimated result is This is because it is the server device 40 that performs retransmission using the retransmission timer and high-speed retransmission. Since the notification destination is the server device 40, notification can be performed without increasing traffic by using the confirmation response segment.

  FIG. 4 is a block diagram showing the configuration of the server device 40. As is apparent from this figure, the server device 40 has a configuration in which the CPU 41 executes a program stored in the nonvolatile memory 42 by using the RAM 43 as a work area and performs various processes in the same manner as a general computer. It has become. The non-volatile memory 42 also includes a control program for controlling execution of the program, a communication program 421 for performing communication processing according to general TCP and replacement control processing described later in the transport layer, and A program for performing communication processing in a layer other than the transport layer is stored. The CPU 41 reads and executes the control program from the nonvolatile memory 42 when a power supply (not shown) is turned on.

  The communication interface 44 transmits and receives signals to and from the core network 30. When data to be transmitted is supplied from the CPU 41, the communication interface 44 transmits a signal modulated by the transmission data to the core network 30. When the data is demodulated from the signal supplied from, the received data is supplied to the CPU 41. The communication interface 44 and the CPU 41 transmit / receive data to / from the mobile device 10 via the core network 30. The CPU 41 executing the control program reads the communication program 421 from the nonvolatile memory 42 and executes it in response to a request from the mobile device 10. As a result, the CPU 41 performs communication processing according to general TCP and switching control processing in the transport layer.

  In communication processing according to general TCP, the CPU 41 writes the number of times that duplicate confirmation response segments have been continuously received (hereinafter referred to as the number of consecutive times) in the RAM 43 for high-speed retransmission. The number of consecutive times stored in the RAM 43 is updated each time the CPU 41 receives a duplicate confirmation response segment. Further, when the CPU 41 transmits the data segment, it starts a retransmission timer for the data segment. The retransmission timer is started by the CPU 41 setting an initial value in the retransmission timer. Setting the initial value to the retransmission timer means that the CPU 41 stores a round-trip propagation delay (RTT: Round-Trip) between the transmission and reception nodes in a storage area secured in the RAM 43 in order to hold the timer value (count value) of the retransmission timer. This refers to writing a retransmission timeout value that is dynamically set based on an actual measurement value of (Time). The started retransmission timer counts down the timer value and times out when the timer value becomes “0”. When the retransmission timer times out, the CPU 41 retransmits the timed out data segment and narrows the congestion window.

  In the switching control process, when the CPU 41 receives the confirmation response segment from the mobile device 10, the CPU 41 does nothing if the EON bit of the confirmation response segment is OFF. Conversely, when the EON bit is on, the CPU 41 temporarily stops the data segment retransmission operation using the ACK value of the confirmation response segment as a sequence number. As retransmission operations to be canceled, there are time counting by a retransmission timer and counting the number of consecutive times for high-speed retransmission. Note that the stop of timing by the retransmission timer also means the stop of the operation for narrowing the congestion window.

  The stop of timing by the retransmission timer is performed by the CPU 41 resetting the timer value of the retransmission timer. The retransmission timer whose timer value has been reset restarts the countdown from the reset value. The reset timer value is a value obtained by adding a preset addition value to the timer value immediately before resetting. Although this added value is an arbitrary positive value, in the present embodiment, a value corresponding to the transmission time interval between data segments when the data segment is transmitted without waiting for the arrival of the acknowledgment segment is used as the added value. The reason why such an addition value is used is to suppress the possibility of unexpected adverse effects caused by resetting the timer value. For example, if the addition value is too large, there is a high possibility that the timeout timing of the retransmission timer will be postponed more than necessary. On the other hand, if the added value is too small, there is a high possibility that the retransmission timer will time out before arrival of the next acknowledgment segment even if the timer value of the retransmission timer immediately before the timeout is reset. This situation is undesirable because the significance of postponing the retransmission timeout timing is diminished. In addition, it is conceivable that the timer value is set to the initial value (retransmission timeout value) without using the added value. However, in this case, there is a high possibility that the timeout timing of the retransmission timer is postponed more than necessary. Become. In this embodiment, the possibility is reduced by determining the addition value as described above. The added value depends on the communication bandwidth between the server device 40 and the core network 30, and is also a value corresponding to this communication bandwidth. Further, instead of setting the addition value in advance, the CPU 41 may actually measure or estimate the transmission time interval between the data segments, and dynamically determine based on the actually measured value or the estimated value.

  The stop of counting the number of continuous times is performed by the CPU 41 updating the number of continuous times written in the RAM 43 and setting the value to 2. In this case, the CPU 41 skips the continuous count process. For this reason, the number of continuous times after the update triggered by reception of the confirmation response segment is “2”. Of course, the CPU 41 does not skip the counting process of the continuous number, sets the continuous number to “1” in anticipation of the counting process, and sets the continuous number to “2” by the counting process triggered by reception of the confirmation response segment. It may be updated. Note that the number of consecutive updates after the reception of the acknowledgment segment is set to the maximum value that does not satisfy the retransmission threshold (that is, “2”) because the data segment indicated by the ACK value of the acknowledgment segment is the last This is to reduce the retransmission delay when the base station 20 is discarded.

[Operation]
Next, the operation of the communication system 100 configured as described above will be described. However, it is assumed that a transport layer communication connection is established between the mobile device 10 and the server device 40 with the base station 20 as a relay device. Therefore, in the following description, the CPU 21 of the base station 20 has already read and executed the control program and the notification program 221 from the nonvolatile memory 22, and the CPU 41 of the server device 40 has already read the control program and the communication program from the nonvolatile memory 42. Assume that 421 is read and executed. Further, it is assumed that the sequence number “0” is written in the duplication determination area 232 of the RAM 23 of the base station 20.

  First, a new drawing referred to in the following description will be described. FIG. 5 is a flowchart showing a part of the notification process performed by the CPU 21 executing the notification program 221, and FIG. 6 is a flowchart showing another flow of the notification process. The processes shown in these two flowcharts are executed in parallel by the CPU 21. FIG. 7 is a flowchart showing the flow of the replacement control process performed by the CPU 41 executing the communication program 421. FIG. 8 is a sequence diagram illustrating an example of communication performed by the communication system 100, and FIG. 9 is a sequence diagram when communication similar to the communication illustrated in FIG. 8 is performed in a general communication system. The general communication system in FIG. 9 is a communication system obtained by removing the function of performing notification processing from the base station 20 of the communication system 100 and replacing the server device 40 of the communication system 100 with control processing. is there.

  As illustrated in FIG. 8, the CPU 41 of the server device 40 sequentially transmits all data segments (data segments having a sequence number of 500 to 2500) within the congestion window. These data segments arrive at the base station 20 in the order transmitted from the server device 40.

  When receiving the data segment with the sequence number “500” (step SA1 in FIG. 5), the CPU 21 of the base station 20 determines whether the received segment is a data segment (whether it is not an acknowledgment segment) ( Step SA2). Since the received segment is a data segment, the CPU 21 writes status data indicating that the status of the received data segment is “transferring” to the status area 231 of the RAM 23, and stores the data segment from the snoop module to a lower layer. (Steps SA3 and SA4). The transfer of the data segment from the server device 40 to the lower layer by the CPU 21 is equivalent to the CPU 21 transmitting the data segment to the mobile device 10.

  Thereafter, in the base station 20, the same processing as described above is repeated, and the status data indicating that the status of the data segment having the sequence number 1000 to 2500 is “transferring” is written in the status area 231 of the RAM 23, These data segments are sequentially transmitted to the mobile device 10. However, in this communication example, the data segment with the sequence number “1000” is delayed in the wireless section between the base station 20 and the mobile device 10. Therefore, the data segment with the sequence number “1000” arrives at the mobile station 10 after the data segment with the sequence number “2500”.

  The mobile device 10 receives the data segment with the sequence number “500” and returns an acknowledgment segment with an ACK value of 1000 for confirming reception of this data segment. Next, the mobile device 10 receives the data segment with the sequence number “1500”. At this time, the sequence number that the mobile device 10 expects to receive is 1000 and not 1500, so the mobile device 10 returns an acknowledgment segment with an ACK value of 1000 for confirming reception of the data segment. To do. This acknowledgment segment is a duplicate acknowledgment segment because its ACK value is the same as the ACK value of the acknowledgment segment transmitted immediately before from the mobile station 10. Thereafter, in the mobile device 10, the same processing as described above is repeated, and two duplicate confirmation response segments are returned. Then, the mobile device 10 receives the data segment with the sequence number “1000” and returns an acknowledgment segment with an ACK value of 3000 for confirming reception of this data segment. Thus, the acknowledgment segment transmitted from the mobile device 10 arrives at the base station 20 in the order of transmission.

  After transmitting the data segment with the sequence number 1500 to the mobile device 10, the CPU 21 of the base station 20 receives the confirmation response segment for confirming reception of the data segment with the sequence number “500” (step SA1). When receiving this confirmation response segment, the CPU 21 determines whether or not the received segment is a data segment (whether or not it is a confirmation response segment) (step SA2). Since the received segment is the confirmation response segment, the CPU 21 determines whether or not the confirmation response segment is a duplicate confirmation response segment (step SA5). This determination is performed by the CPU 21 comparing the sequence number written in the duplication determination area 232 of the RAM 23 with the ACK value of the confirmation response segment.

  Here, since the sequence number “0” written in the duplication determination area 232 is smaller than the ACK value “1000” of the confirmation response segment, it is determined that the confirmation response segment is not a duplication confirmation response segment. Therefore, the CPU 21 performs reception confirmation processing (step SA6). In the reception confirmation process, the CPU 21 overwrites the state data of the data segment written in the state area 231 with the state data indicating that the state of the data segment to be confirmed by the confirmation response segment is “reception”. . Here, since the data segment whose reception is confirmed by the confirmation response segment is the data segment with the sequence number “500”, the status data of the data segment with the sequence number “500” is updated to indicate “reception”. . In the reception confirmation process, the CPU 21 overwrites the overlap determination area 232 with the ACK value of the confirmation response segment. Here, since the ACK value of the confirmation response segment is 1000, the sequence number “1000” is written in the duplication determination area 232.

  Next, the CPU 21 passes the confirmation response segment from the snoop module to the lower layer (step SA4). The transfer of the confirmation response segment from the mobile device 10 to the lower layer by the CPU 21 means that the CPU 21 transmits the confirmation response segment to the server device 40.

  Further, after transmitting the data segment with the sequence number 2500 to the mobile device 10, the CPU 21 receives the confirmation response segment for confirming the reception of the data segment with the sequence number “1500” (step SA1). Since this segment is an acknowledgment segment, as described above, the CPU 21 determines whether or not the acknowledgment segment is a duplicate acknowledgment segment (steps SA2: NO and SA5). Here, since the sequence number written in the duplication determination area 232 is 1000 and the ACK value of the confirmation response segment is 1000, it is determined that the confirmation response segment is a duplication confirmation response segment. Therefore, the CPU 21 determines whether or not the state of the data segment whose sequence number is the ACK value of the confirmation response segment is “transferring” (step SA7). Since the status data written in the status area 231 indicates that the status of the data segment with the sequence number “1000” is “being transferred”, the CPU 21 sets the EON bit of the confirmation response segment to ON. (Step SA8). Next, the CPU 21 transmits an acknowledgment segment with the EON bit set to ON to the server device 40 (step SA4).

  The state of the data segment with the sequence number “1000” changes from “in transit” to “receive” after the CPU 21 receives the acknowledgment segment for confirming the receipt of the data segment with the sequence number “1000”. The CPU 21 further receives two duplicate confirmation response segments before receiving the confirmation response segment. Therefore, the CPU 21 continuously transmits three duplicate confirmation response segments having the EON bit set to ON to the server device 40 (steps SA1, SA2: NO, SA5: YES, SA7: YES, SA8, and SA4). .

Next, the CPU 21 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “1000” (step SA1). Since this segment is an acknowledgment segment and not a duplicate acknowledgment segment, the CPU 21 performs reception confirmation processing and transmits the acknowledgment segment to the server device 40 (steps SA2: NO, SA5: NO, SA6, and SA4). ). As a result, the sequence number “3000” is written in the duplication determination area 232, and the status data written in the status area 231 for the data segment having the sequence numbers of 500 to 2500 is updated to indicate “reception”.
The confirmation response segments transmitted from the base station 20 as described above arrive at the server device 40 in the order of transmission.

  The CPU 41 of the server device 40 receives the confirmation response segment for confirming the reception of the data segment with the sequence number “500” after transmitting the data segment with the sequence number 2500 to the mobile device 10 (step SB1 in FIG. 7). . When receiving the confirmation response segment, the CPU 41 determines whether or not the EON bit of this confirmation response segment is set to ON (step SB2). Since the EON bit of the received acknowledgment segment is set to OFF, the CPU 41 performs only processing according to general TCP (step SB2: NO). That is, the congestion window is slid by one data segment, and the data segment with the sequence number “3000” is transmitted to the mobile device 10.

  This data segment is received by the CPU 21 of the base station 20 after the transmission of the second duplication confirmation response segment and before the transmission of the third duplication confirmation response segment, and is transferred to the mobile device 10. During this transfer, state data indicating that the state of the data segment with the sequence number “3000” is “being transferred” is written in the state area 231 of the base station 20.

  The data segment with the sequence number “3000” transferred from the base station 20 is received by the mobile device 10 after the transmission of the acknowledgment segment for confirming the reception of the data segment with the sequence number “1000”. The mobile station 10 returns an acknowledgment segment with an ACK value of 3500 for confirming reception of this data segment. The confirmation response segment is received by the CPU 21 of the base station 20 after receiving the confirmation response segment for confirming the reception of the data segment with the sequence number “1000” and transferred to the server device 40. During this transfer, the status data written in the status area 231 of the base station 20 for the data segment with the sequence number “3000” is updated to data indicating “reception”.

  The CPU 41 of the server apparatus 40 receives an acknowledgment segment for confirming the reception of the data segment with the sequence number “1500” following the acknowledgment segment for confirming the reception of the data segment with the sequence number “500” (step SB1). Since the EON bit of this acknowledgment segment is set to ON, the CPU 41 temporarily stops the data segment retransmission operation using the ACK value of the acknowledgment segment as a sequence number (steps SB2: YES and SB3). ). Specifically, the CPU 41 resets a value obtained by adding a predetermined addition value to the timer value of the retransmission timer of the data segment as the timer value of the timer, while updating the continuous number of times written in the RAM 43. Then, the value is set to 2, and the counting process of the continuous number is skipped. Of course, also during this period, out of the processes according to the general TCP, the processes other than the temporarily stopped processes are continuously performed.

  Next, the CPU 41 sequentially receives confirmation response segments for confirming the reception of the data segments having the sequence numbers “2000” and “2500”, and confirming these for confirming the reception of the data segment having the sequence number “1500”. The same processing as when the response segment is received is repeated (steps SB1, SB2: YES and SB3). Next, the CPU 41 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “1000” (step SB1). Since the EON bit of the confirmation response segment is set to OFF, the CPU 41 performs only processing according to general TCP (step SB2: NO). As a result, the CPU 41 starts the process of sliding the congestion window and sequentially transmitting the data segments having the sequence numbers of 3500 to 5500.

  Here, the features of the above-described operation will be described with reference to FIG. As shown in FIG. 9, in a general communication system, when the server apparatus receives three consecutive duplicate acknowledgment segments, the data segment with the ACK value of the duplicate acknowledgment segment as a sequence number disappears. The data segment is retransmitted (high-speed retransmission). However, the data segment regarded as lost is actually received by the mobile device. That is, the above retransmission is an improper retransmission caused by erroneously detecting the change of the reception order of the data segments in the mobile device as the loss of the data segments. On the other hand, in this embodiment, as apparent from FIG. 8, even if the server device 40 receives three consecutive acknowledgment segments, these EON bits are set to ON. Will not be resent. That is, according to the present embodiment, it is possible to prevent inappropriate high-speed retransmission due to erroneous detection of the change of the reception order of the data segments in the mobile device 10 as the loss of the data segments.

Subsequently, the operation of the communication system 100 will be described.
As shown in FIG. 8, the CPU 41 of the server device 40 confirms the reception of the data segment with the sequence number “3000” while performing the process of sequentially transmitting the data segments with the sequence numbers 3500 to 5500. A response segment is received (step SB1). Since the EON bit of the confirmation response segment is set to OFF, the CPU 41 performs only processing according to general TCP (step SB2: NO). As a result, the CPU 41 performs a process of further sliding the congestion window and sequentially transmitting data segments having a sequence number up to 6000. These data segments arrive at the base station 20 in the order transmitted from the server device 40.

  When the CPU 21 of the base station 20 receives the data segment with the sequence number “3500”, since the received segment is a data segment, status data indicating that the status of this data segment is “transferring” is stored in the state of the RAM 23. The data segment is written in the area 231 and this data segment is transmitted to the mobile device 10 (steps SA1, SA2: YES, SA3, and SA4). Thereafter, the base station 20 repeats the same processing as described above, and the status data indicating that the status of the data segment having the sequence number of 4000 to 6000 is “transferring” is written in the status area 231 of the RAM 23, These data segments are sequentially transmitted to the mobile device 10.

  However, in this communication example, a data segment with a sequence number of 3500 to 4500 disappears in the wireless section between the base station 20 and the mobile device 10. Therefore, the data segment that mobile station 10 receives after the data segment with sequence number “3000” is the data segment with sequence number “5000”. When the mobile station 10 receives the data segments having the sequence numbers of 5000 to 6000 in sequence, the mobile station 10 returns the acknowledgment segments having the ACK value 3500 for confirming the reception of these data segments in order. These acknowledgment segments are all duplicate acknowledgment segments.

  After transmitting the data segment with the sequence number “6000” to the mobile device 10, the CPU 21 of the base station 20 receives the acknowledgment segment for confirming the reception of the data segment with the sequence number “5000” (step SA1). Since this confirmation response segment is a duplicate confirmation response segment, the CPU 21 determines whether or not the state of the data segment whose sequence number is the ACK value “3500” of this confirmation response segment is “Transferring” (Step S21). SA2: NO, SA5: YES, and SA7). At this time, since the state of the data segment is “transferring”, the CPU 21 sets the EON bit of the confirmation response segment to ON and transmits the confirmation response segment after setting to the server device 40 (step SA8). And SA4).

  Next, the CPU 21 discards the data segment having the sequence number “3500” due to a timeout or the like in a layer lower than the transport layer (specifically, the RLC sublayer). CPU21 acquires the discard notification which shows this from a lower layer in a snoop module (step SC1). Upon obtaining the discard notification, the CPU 21 obtains the status data of the data segment written in the status area 231 of the RAM 23 with the status data indicating that the status of the data segment of the sequence number indicated in the discard notification is “discard”. Overwrite (step SC2).

  Next, the CPU 21 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “5500” (step SA1). Since this confirmation response segment is a duplicate confirmation response segment, the CPU 21 determines whether or not the state of the data segment whose sequence number is the ACK value “3500” of this confirmation response segment is “Transferring” (Step S21). SA2: NO, SA5: YES, and SA7). At this time, since the state of the data segment is “discard”, the CPU 21 transmits the confirmation response segment to the server device 40 as it is (step SA4).

Thereafter, the base station 20 repeats the same processing as described above, and the confirmation response segment for confirming reception of the data segment with the sequence number “6000” is transferred to the server device 40 as it is.
The confirmation response segments transmitted from the base station 20 as described above arrive at the server device 40 in the order of transmission.

  After transmitting the data segment with the sequence number “6000” to the mobile device 10, the CPU 41 of the server device 40 receives the confirmation response segment for confirming the reception of the data segment with the sequence number “5000” (step SB1). Since the EON bit of this acknowledgment segment is set to ON, the CPU 41 temporarily stops the data segment retransmission operation with the ACK value “3500” of the acknowledgment segment as a sequence number (step SB2: YES). And SB3). As a result, the timeout timing of the retransmission timer of the data segment is postponed, and the number of consecutive times for high-speed retransmission is 2.

  Next, the CPU 41 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “5500” (step SB1). Since the EON bit of the confirmation response segment is set to OFF, the CPU 41 performs only processing according to general TCP (step SB2: NO). That is, 1 is added to the number of consecutive times for high-speed retransmission. As a result, since the number of consecutive times reaches the retransmission threshold, the CPU 41 retransmits the data segment with the ACK value “3500” of the confirmation response segment as a sequence number.

  Here, the features of the above-described operation will be described with reference to FIG. As shown in FIG. 9, in a general communication system, the retransmission timer of the data segment with the sequence number “3500” times out before three duplicate acknowledgment segments arrive at the server device, and the data The segment is retransmitted. On the other hand, in this embodiment, as is apparent from FIG. 8, the data segment is retransmitted by high-speed retransmission before the retransmission timer times out. Retransmission due to timeout in communication conforming to TCP involves a process that significantly narrows the congestion window, whereas retransmission by high-speed retransmission does not involve such a process, and therefore this embodiment is more efficient in subsequent communications. A communication network can be used.

  As described above, according to the present embodiment, since the order of SDUs is not controlled in the RLC sublayer, the substantial utilization rate of the communication network does not decrease. In addition, according to the present embodiment, a situation that occurs in the transport layer by not performing SDU order control in the RLC sublayer, and erroneously detecting a change in the reception order of data segments as a loss of data segments. Inappropriate flow control due to the situation is not performed. Therefore, the substantial utilization rate of the communication network can be improved.

  In the above description of the operation, a description of a case where it is an error to consider a data segment loss when a retransmission timer times out in a general communication system is omitted. This has already been described that when the acknowledgment segment with the EON bit set to ON is received, the timing of the retransmission timer is temporarily stopped and the timeout timing is postponed. This is because it can be easily understood that this embodiment can avoid a situation in which a timeout occurs accidentally.

  By the way, in the above-described embodiment, in order to reduce the retransmission delay, the server apparatus 40 sets the maximum number “2” at which the number of consecutive times does not satisfy the retransmission threshold when receiving the acknowledgment segment in which the EON bit is set to ON. It is set up. However, it is possible to reduce the retransmission delay even if the continuous count is set to the initial value “0” when the acknowledgment segment with the EON bit set to ON is received. Such an embodiment will be described next.

[Second Embodiment]
[Constitution]
FIG. 10 is a diagram showing a configuration of a communication system 200 according to the second embodiment of the present invention. The communication system 200 is different from the communication system 100 of FIG. 1 only in that it has a base station 50 instead of the base station 20 and a server device 60 instead of the server device 40. The communication protocol configuration of the base station 50 is the same as that of the base station 20, and the communication protocol configuration of the server device 60 is the same as that of the server device 40.

  FIG. 11 is a block diagram showing the configuration of the base station 50. The only difference between the base station 50 and the base station 20 is that the nonvolatile memory 22 stores a notification program 521 instead of the notification program 221. The notification program 521 starts / ends in conjunction with establishment of a transport layer communication connection with the base station 50 as a relay device. Hereinafter, a part of the notification process performed by the CPU 21 executing the notification program 521 that is different from the notification process performed by the CPU 21 executing the notification program 221 will be described.

  When receiving the confirmation response segment from the mobile device 10 in the notification process, the CPU 21 executing the notification program 521 compares the sequence number written in the duplication determination area 232 of the RAM 23 with the ACK value of the confirmation response segment. When the former is not younger than the latter, the CPU 21 determines whether or not the state of the data segment having the sequence number as the ACK value of the confirmation response segment is “discard”. Then, the erasure notification bit of the confirmation response segment is set to ON, and the confirmation response segment after the setting is transmitted to the server device 60. The erasure notification bit is one bit in an unused area of a data segment in general TCP, and is set to off by default, and is not used in communication according to general TCP. This mechanism of loss notification is realized by using a well-known ELN (Explicit Loss Notification). As is clear from this, the server device 60 corresponds to ELN. Conversely, if it is not “discard”, the CPU 21 determines whether or not the state of the data segment whose sequence number is the ACK value of the confirmation response segment is “transferring”, and is not “transferring”. The confirmation response segment is transferred to the server device 60 as it is. If “transfer in progress”, the CPU 21 sets the EON bit of the confirmation response segment to ON, and transmits the confirmation response segment after setting to the server device 60.

  FIG. 12 is a block diagram illustrating a configuration of the server device 60. The configuration differs from the server device 40 only in that the nonvolatile memory 42 stores a communication program 621 instead of the communication program 421 and is compatible with ELN. The communication program 621 is executed in response to a request from the mobile device 10. In the following, of the replacement control processing performed by the CPU 41 executing the communication program 621, the replacement performed by the CPU 21 executing the communication program 421. Differences from the control process will be described.

  When receiving the confirmation response segment from the mobile device 10, the CPU 41 that is executing the communication program 621 determines whether or not the disappearance notification bit of the confirmation response segment is on. If it is on, the ACK value of the confirmation response segment is determined. It is determined whether or not the forced retransmission flag for the data segment having the sequence number as ON is ON. The forced retransmission flag is written in the RAM 43, and its default value is off. Only when the forced retransmission flag is off, the CPU 41 immediately retransmits the data segment and turns on the forced retransmission flag for the data segment. The state of the server device 40 after the retransmission is the same as the state after the data segment is retransmitted by high-speed retransmission. Note that the ON / OFF of the EON bit is determined only when the disappearance notification bit of the confirmation response segment is OFF. Further, when the EON bit of the received acknowledgment segment is set to ON, the CPU 41 sets the continuous count to 0 instead of 2.

[Operation]
Next, among the operations of the communication system 200 having the above-described configuration, points that are significantly different from the operations of the communication system 100 in FIG. 1 will be described mainly with reference to FIGS. FIG. 13 is a flowchart showing a part of the notification process performed by the CPU 21 executing the notification program 521. The process shown in this flowchart and the process shown in FIG. 6 are executed in parallel by the CPU 21. FIG. 14 is a flowchart showing the flow of the replacement control process performed by the CPU 41 executing the communication program 621. FIG. 15 is a sequence diagram illustrating an example of communication performed by the communication system 200. Note that the premise in this operation description is the same as the premise of the operation description of the first embodiment.

  As shown in FIG. 15, after transmitting the data segment with the sequence number “6000” to the mobile station 10, the CPU 21 of the base station 50 receives the acknowledgment segment for confirming the reception of the data segment with the sequence number “5000”. (Step SA1). Since this confirmation response segment is a duplicate confirmation response segment, the CPU 21 determines whether or not the state of the data segment with the ACK value “3500” of this confirmation response segment as a sequence number is “discard” (step SA2). : NO, SA5: YES, and SD1). At this time, since the state of the data segment is not “discarded”, the CPU 21 determines whether or not the state of the data segment having the ACK value “3500” of the acknowledgment segment as a sequence number is “transferring”. Determine (step SA7). At this time, since the state of the data segment is “transferring”, the CPU 21 sets the EON bit of the confirmation response segment to ON and transmits the confirmation response segment after setting to the server device 40 (step SA8). And SA4).

  Next, the CPU 21 discards the data segment having the sequence number “3500” due to a timeout or the like in a layer lower than the transport layer (specifically, the RLC sublayer). CPU21 acquires the discard notification which shows this from a lower layer in a snoop module (step SC1 of FIG. 6). Upon obtaining the discard notification, the CPU 21 obtains the status data of the data segment written in the status area 231 of the RAM 23 with the status data indicating that the status of the data segment of the sequence number indicated in the discard notification is “discard”. Overwrite (step SC2).

  Next, the CPU 21 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “5500” (step SA1). Since this confirmation response segment is a duplicate confirmation response segment, the CPU 21 determines whether or not the state of the data segment with the ACK value “3500” of this confirmation response segment as a sequence number is “discard” (step SA2). : NO, SA5: YES, and SD1). At this time, since the state of the data segment is “discard”, the CPU 21 sets the disappearance notification bit of the confirmation response segment to ON, and transmits the confirmation response segment after the setting to the server device 60 (step) SD2 and SA4).

Thereafter, the base station 20 repeats the same processing as described above, and an acknowledgment segment for confirming reception of the data segment with the sequence number “6000”, in which the acknowledgment segment with the erasure notification bit set to ON is obtained. It is transferred to the server device 60.
The confirmation response segments transmitted from the base station 50 as described above arrive at the server device 60 in the order of transmission.

  After transmitting the data segment with the sequence number “6000” to the mobile device 10, the CPU 41 of the server device 60 receives the confirmation response segment for confirming the reception of the data segment with the sequence number “5000” (step SB1). Since the erasure notification bit of the acknowledgment segment is set to OFF and the EON bit is set to ON, the CPU 41 sets the ACK value “3500” of the acknowledgment segment as a sequence number. The retransmission operation is temporarily stopped (step SE1: NO, SB2: YES, and SB3).

  Next, the CPU 41 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “5500” (step SB1). Since the erasure notification bit of this acknowledgment segment is set to ON and the forced retransmission flag for the data segment having the ACK value of the acknowledgment segment as a sequence number is OFF, the CPU 41 immediately sets the data segment. And the forced retransmission flag for the data segment is turned on (steps SE1: YES, SE2: NO, and SE3).

  Next, the CPU 41 receives an acknowledgment segment for confirming reception of the data segment with the sequence number “6000” (step SB1). Since the erasure notification bit of this acknowledgment segment is set on and the forced retransmission flag for the data segment with the ACK value of the acknowledgment segment as a sequence number is on, the CPU 41 retransmits the data segment. No (step SE1: YES and SE2: YES). Thereby, useless retransmission is avoided.

  As described above, in this embodiment, even when the server device 60 receives an acknowledgment segment in which the EON bit is set to ON, even if the number of consecutive times becomes 0, the loss notification bit notifies the loss of the data segment. Then, since the corresponding data segment is immediately retransmitted, the same kind of effect as in the first embodiment can be obtained.

[Third Embodiment]
FIG. 16 is a diagram showing a configuration of a communication system 300 according to the third embodiment of the present invention. The communication system 300 is different from the communication system 100 in FIG. 1 in that it has a mobile device 70 instead of the mobile device 10, a base station 80 instead of the base station 20, and a server device 40. It is only the point which has the server apparatus 90. The communication protocol configuration of the communication system 300 is the same as the configuration shown in FIG. However, the mobile device 70 and the server device 90 communicate using a TCP SACK option.

  FIG. 17 is a block diagram showing the configuration of the base station 80. In terms of configuration, the base station 80 differs from the base station 20 only in that the non-volatile memory 22 stores a notification program 821 instead of the notification program 221 and that the overlap determination area 232 is not secured in the RAM 23. . This notification program 821 starts / ends in conjunction with the establishment of a transport layer communication connection with the base station 80 as a relay device.

  FIG. 18 is a flowchart showing a part of the notification process performed by the CPU 21 executing the notification program 821. The process shown in this flowchart and the process shown in FIG. 6 are executed in parallel by the CPU 21. As shown in FIG. 18, when the CPU 21 executing the notification program 821 receives a segment from the server device 90 (step SA1), it is determined whether the received segment is a data segment (whether it is not an acknowledgment segment). Is determined (step SA2). When the received segment is a data segment, the CPU 21 writes status data indicating that the status of the data segment is “transferring” to the status area 231 of the RAM 23 and transfers the data segment to the mobile device 70 (step S31). SA3 and SA4).

  Conversely, if the received segment is not a data segment, that is, if it is an acknowledgment segment, the CPU 21 determines whether or not a new acknowledgment has been made based on the ACK value of the acknowledgment segment and the contents of the SACK block. Determination is made (step SF1). The SACK block is a block that the confirmation response segment has in communication according to TCP using the SACK option, and includes first to fourth SACK blocks. Each block stores a sequence number as necessary. By referring to the content of the SACK block and the ACK value, the server device 90 can specify the data segment received by the mobile device 70.

  When a new reception confirmation is made by the confirmation response segment, the CPU 21 performs a reception confirmation process (steps SF1: YES and SF2). In this reception confirmation process, the CPU 21 updates the status data of the data segment whose reception is confirmed by the confirmation response segment so as to indicate “reception”. Next, the CPU 21 determines whether or not there is a possibility that the data segment is switched (step SF3). If no new reception confirmation is made by the confirmation response segment, the CPU 21 determines whether or not there is a possibility that the data segment has been switched without performing the reception confirmation process (step S21). SF1: NO and SF3).

  To determine whether there is a possibility that data segment replacement has occurred, specify the youngest sequence number among the sequence numbers of the data segments whose status indicated by the status data is “Transferring”. Is realized by checking whether or not the SACK block of the acknowledgment segment has a large sequence number. When such a sequence number does not exist in the SACK block, the CPU 21 determines that there is no possibility that the data segment has been switched, and transfers the confirmation response segment to the server device 90 as it is (step SA4). Conversely, when such a sequence number exists in the SACK block, the CPU 21 determines that there is a possibility that the data segment has been replaced, and specifies the replaced data segment (step SF4). The identification of the replacement data segment is realized by finding a data segment having a lower sequence number than the data segment confirmed by the SACK block of the acknowledgment segment and whose state is not “received”.

  If the data segment status is neither “transferring” nor “discarded”, the CPU 21 that has identified the replacement data segment transfers the confirmation response segment to the server device 90 as it is (steps SF5: NO, SF6: NO and SA4). On the other hand, when the state of the data segment is “discard”, the CPU 21 performs the disappearance notification process, and then transmits the confirmation response segment to the server device 90 (step SF5: YES, SF7, and SA4). . The erasure notification process includes a process of turning on the erasure notification bit of the confirmation response segment and a process of storing the sequence number of the data segment in a predetermined field of the confirmation response segment. On the other hand, when the state of the data segment is “transferring”, the CPU 21 performs a replacement notification process, and thereafter transmits the confirmation response segment to the server device 90 (step SF5: NO, SF6: YES, SF8). And SA4). The replacement notification process includes a process of turning on the EON bit of the confirmation response segment and a process of storing the sequence number of the data segment in a predetermined field of the confirmation response segment. In the present embodiment, the first SACK block is adopted as the predetermined field. That is, the CPU 21 moves the contents of the first SACK block to the second SACK block, the contents of the second SACK block to the third SACK block, and so on, and then stores the sequence number of the data segment in the first SACK block. .

  FIG. 19 is a block diagram illustrating a configuration of the server device 90. The server device 90 is different from the server device 40 in terms of configuration in that the nonvolatile memory 42 stores a communication program 921 instead of the communication program 421, and corresponds to the TCP SACK option. It is only a point corresponding to. This communication program 921 is executed in response to a request from the mobile device 70.

  FIG. 20 is a flowchart showing the flow of the replacement control process performed by the CPU 41 executing the communication program 921. As shown in this figure, when the CPU 41 executing the communication program 921 receives the confirmation response segment from the mobile device 10 (step SB1), it determines whether or not the disappearance notification bit of the confirmation response segment is on (step SB1). If SE1) is off, it is determined whether or not the EON bit of the confirmation response segment is set on (step SB2). If the EON bit is set to OFF, the CPU 41 performs only processing according to general TCP using the SACK option (step SB2: NO). Conversely, if the EON bit is set to ON, the scoreboard is updated so that the state of the data segment of the sequence number stored in the first SACK block of the acknowledgment segment becomes “Sacked”. The data segment retransmission operation is temporarily stopped (step SB2: YES and SG1).

  On the other hand, if the erasure notification bit of the received acknowledgment segment is on, the CPU 41 determines whether or not the forced retransmission flag for the data segment of the sequence number stored in the first SACK block of the acknowledgment segment is on ( Step SG2). The forced retransmission flag is written in the RAM 43, and its default value is off. Only when the forced retransmission flag for the data segment is off, the CPU 41 immediately retransmits the data segment and turns on the forced retransmission flag for the data segment (steps SG2: NO and SG3).

  Since the communication process performed by the communication system 300 according to the present embodiment is as described above, according to the present embodiment, the same type of effect as the first embodiment can be obtained.

[Deformation]
Below, the modification of embodiment mentioned above is enumerated.
In the above-described embodiment, the wireless path is included in the communication path between the transmission node (server device) and the reception node (mobile device) in the transport layer. However, the communication path is configured only by the wired section. It may be. Of course, the network between the transmitting node and the receiving node may not be compliant with IMT-2000. In short, any network may be used as long as the transmission node and the reception node can communicate in the transport layer.
In the above-described embodiment, the relay node between the transmission node and the reception node in the transport layer notifies the switching of the data segment. However, the reception node may perform the notification.
In the above-described embodiment, the change of the data segment is notified using the confirmation response segment. However, the notification may be performed using other data depending on the communication protocol of the transport layer.
In the above-described embodiment, the relay node uses the acknowledgment segment returned from the receiving node to notify the data segment replacement. However, the relay node generates the acknowledgment segment and uses this You may make it perform notification of replacement.
In the above-described embodiments, the present invention is used for retransmission control and congestion control. However, the present invention may be used for transmission rate control based on the data loss rate. When the node for obtaining the data loss rate is the receiving node, the notification destination of the data segment replacement is the receiving node. Therefore, when the receiving node notifies the replacement of data segments, the existing ones can be used as they are as the transmitting node and the relay node.
In addition, in a control node that performs various controls such as retransmission control, congestion control, transmission rate control, etc., after receiving notification of a data segment whose reception order has been changed in the receiving node, the data segment is If it is determined that the node has disappeared, the state of the control node may be set to the state in the case where there is no temporary suspension. For example, after the retransmission timer is temporarily stopped, the timer value may be advanced by the amount corresponding to the temporary stop period, and then the retransmission timer may be restarted.
In the above-described embodiment, the replacement of the data segment is estimated using the data segment and the confirmation response segment. However, in the case of the communication protocol in which the transport layer communication protocol does not regulate the transmission of the confirmation response segment. Alternatively, when the replacement of the data segment is estimated at the receiving node, the replacement of the data segment may be estimated using only the data segment. In the first place, the ACK value of the acknowledgment segment and the sequence number of the SACK block are based on the sequence number of the transport segment data segment received by the receiving node. The estimation is also within the scope of estimating a data unit whose reception order in the receiving node is changed based on the sequence number of the transport layer data unit received by the receiving node.

1 is a diagram showing a configuration of a communication system 100 according to a first embodiment of the present invention. 1 is a diagram illustrating a communication protocol configuration of a communication system 100. FIG. 1 is a block diagram showing a configuration of a base station 20 that constitutes a communication system 100. FIG. 2 is a block diagram illustrating a configuration of a server device 40 that configures the communication system 100. FIG. 4 is a flowchart showing a part of a notification process performed by a CPU 21 executing a notification program 221 in a base station 20. 12 is a flowchart showing another flow of notification processing performed by the CPU 21 executing the notification program 221 in the base station 20. 4 is a flowchart showing the flow of a replacement control process performed by a CPU 41 executing a communication program 421 in the server device 40. 3 is a sequence diagram illustrating an example of communication performed by the communication system 100. FIG. It is a sequence diagram at the time of trying to perform communication similar to the communication shown in FIG. 8 in a general communication system. It is a figure which shows the structure of the communication system 200 which concerns on 2nd Embodiment of this invention. 2 is a block diagram showing a configuration of a base station 50 that constitutes a communication system 200. FIG. 2 is a block diagram illustrating a configuration of a server device 60 that configures a communication system 200. FIG. 6 is a flowchart showing a part of a notification process performed by a CPU 21 executing a notification program 521 in a base station 50. 6 is a flowchart showing the flow of a replacement control process performed by a CPU 41 that is executing a communication program 621 in the server device 60. 3 is a sequence diagram illustrating an example of communication performed by the communication system 200. FIG. It is a figure which shows the structure of the communication system 300 which concerns on 3rd Embodiment of this invention. 2 is a block diagram showing a configuration of a base station 80 that constitutes a communication system 300. FIG. 7 is a flowchart showing a part of a notification process performed by a CPU 21 executing a notification program 821 in a base station 80. 3 is a block diagram illustrating a configuration of a server device 90 that configures the communication system 300. FIG. 10 is a flowchart showing a flow of a replacement control process performed by a CPU 41 executing a communication program 921 in the server device 90.

Explanation of symbols

20, 50, 80 ... base station, 21, 41 ... CPU, 22, 42 ... non-volatile memory, 221, 521, 821 ... notification program, 23, 43 ... RAM, 24 ... radio unit, 25, 44 ... communication interface, 40, 60, 90... Server device, 421, 621, 921.

Claims (10)

Data receiving means for receiving a transport layer data unit transmitted from a transmitter to a receiver and having a number capable of specifying a transmission order from the transmitter;
When the data unit is received by the data receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the receiver. Data transmission means for transmitting to,
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the data receiving unit and transmitted by the data transmitting unit is discarded, it is determined that the data unit is discarded in association with the number of the data unit. Overwrite means for overwriting that the data unit is being transferred, stored in the storage means,
Confirmation response transmitting means for transmitting the confirmation response received by the confirmation response receiving means to the transmitter;
With
The confirmation response transmission means includes:
Comparing the first number included in the confirmation response received by the confirmation response receiving means with the second number of the data unit stored in the second storage means;
When the second number is smaller than the first number, the first number is overwritten in the second storage means as the second number, and a data unit having a number smaller than the first number Is overwritten in the first storage means that it has been received at the receiver, and the confirmation response is transferred to the transmitter,
In the case where the second storage unit stores the fact that the data unit of the first number is discarded when the second number is not younger than the first number, the confirmation response is returned. When it is stored that the data unit of the first number is being transferred while the data unit of the first number is being transferred, the information including the information indicating that the data unit of the first number is being transferred A communication device that transmits an acknowledgment to the transmitter . Data receiving means for receiving a transport layer data unit transmitted from a transmitter to a receiver and having a number capable of specifying a transmission order from the transmitter;
When the data unit is received by the data receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the receiver. Data transmission means for transmitting to,
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the data receiving unit and transmitted by the data transmitting unit is discarded, it is determined that the data unit is discarded in association with the number of the data unit. Overwrite means for overwriting that the data unit is being transferred, stored in the storage means,
Confirmation response transmitting means for transmitting the confirmation response received by the confirmation response receiving means to the transmitter;
With
The confirmation response transmission means includes:
Based on the first number included in the confirmation response received by the confirmation response receiving means and the content stored in a predetermined field of the confirmation response, a new reception confirmation is made by the confirmation response. In the case where a new reception confirmation is made by the confirmation response, it is determined that the data unit for which the new reception confirmation is made has been received by the receiver. Overwrite the storage means,
The predetermined field of the confirmation response stores a number larger than the third number which is the youngest number among the numbers of the data units stored as being transferred by the first storage means. If not, forward the acknowledgment to the transmitter,
When the predetermined field of the confirmation response stores a number larger than the third number, the number has a lower number than the number stored in the predetermined field and is received by the receiver A data unit that has not been overwritten in the first storage means is identified,
When it is stored in the first storage means that the specified data unit is discarded, the first field includes information indicating that the data unit is discarded, and the predetermined field includes the information The confirmation response storing the data unit number is transferred to the transmitter, while the first storage means stores that the identified data unit is being transferred, the data unit transfers The confirmation response including information indicating that the data unit is included and storing the number of the data unit in the predetermined field is transmitted to the transmitter.
Communication device. When the data unit is discarded in a layer lower than the transport layer , the data overwriting means indicates that the data unit is discarded in association with the number of the data unit. 3. The communication apparatus according to claim 1 , wherein the data unit stored in the storage unit is overwritten when the data unit is being transferred . Receiving means for receiving the confirmation response from the communication device according to any one of claims 1 to 3 ,
And loss estimation means for estimating the loss of the data unit based on the order or timing of reception of said data units by receiving machine,
When the confirmation response received by the receiving means includes information indicating that the data unit of the first number included in the confirmation response is being transferred, the loss of the data unit is A transmitter having a prohibition unit for temporarily prohibiting estimation by the erasure estimation unit. A transmitter and a communication device;
The transmitter is
First transmission means for transmitting a transport layer data unit having a number capable of specifying a transmission order to a receiver;
Erasure estimation means for estimating erasure of the data units based on the order or timing of reception of the data units by the receiver;
The communication device
First receiving means for receiving the data unit transmitted from the transmitter;
When the data unit is received by the first receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the data unit. Data transmission means for transmitting to the receiver;
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the first receiving unit and transmitted by the data transmitting unit is discarded, the data unit is discarded in association with the number of the data unit. Overwriting means for overwriting that the data unit is being transferred, stored in the first storage means;
An acknowledgment transmission means for transmitting the acknowledgment received by the acknowledgment receiving means to the transmitter ;
The confirmation response transmission means of the communication device includes:
Comparing the first number included in the confirmation response received by the confirmation response receiving means with the second number of the data unit stored in the second storage means;
When the second number is smaller than the first number, the first number is overwritten in the second storage means as the second number, and a data unit having a number smaller than the first number Is overwritten in the first storage means that it has been received at the receiver, and the confirmation response is transferred to the transmitter,
In the case where the second storage unit stores the fact that the data unit of the first number is discarded when the second number is not younger than the first number, the confirmation response is returned. When it is stored that the data unit of the first number is being transferred while the data unit of the first number is being transferred, the information including the information indicating that the data unit of the first number is being transferred Send an acknowledgment to the transmitter,
The transmitter further includes:
A second receiving means for receiving by said acknowledgment transmitted from the acknowledgment transmitting means,
When the confirmation response received by the receiving means includes information indicating that the data unit of the first number included in the confirmation response is being transferred, the loss of the data unit is And a prohibition unit for temporarily prohibiting estimation by the disappearance estimation unit. A transmitter and a communication device;
The transmitter is
First transmission means for transmitting a transport layer data unit having a number capable of specifying a transmission order to a receiver;
Erasure estimation means for estimating erasure of the data units based on the order or timing of reception of the data units by the receiver;
Have
The communication device
First receiving means for receiving the data unit transmitted from the transmitter;
When the data unit is received by the first receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the data unit. Data transmission means for transmitting to the receiver;
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the first receiving unit and transmitted by the data transmitting unit is discarded, the data unit is discarded in association with the number of the data unit. Overwriting means for overwriting that the data unit is being transferred, stored in the first storage means;
An acknowledgment transmission means for transmitting the acknowledgment received by the acknowledgment receiving means to the transmitter ;
Based on the first number included in the confirmation response received by the confirmation response receiving means of the communication device and the contents stored in a predetermined field of the confirmation response, a new reception confirmation is made by the confirmation response. In the case where a new reception confirmation is made by the confirmation response, it is confirmed that the data unit for which the new reception confirmation is made has been received by the receiver. Overwriting the first storage means;
The predetermined field of the confirmation response stores a number larger than the third number which is the youngest number among the numbers of the data units stored as being transferred by the first storage means. If not, forward the acknowledgment to the transmitter,
When the predetermined field of the confirmation response stores a number larger than the third number, the number has a lower number than the number stored in the predetermined field and is received by the receiver A data unit that has not been overwritten in the first storage means is identified,
When it is stored in the first storage means that the specified data unit is discarded, the first field includes information indicating that the data unit is discarded, and the predetermined field includes the information The confirmation response storing the data unit number is transferred to the transmitter, while the first storage means stores that the identified data unit is being transferred, the data unit transfers Including the information indicating that the data unit is included, and transmitting the confirmation response storing the number of the data unit in the predetermined field to the transmitter,
The transmitter further includes:
Second receiving means for receiving the confirmation response transmitted from the confirmation response transmitting means;
When the confirmation response received by the receiving means includes information indicating that the data unit of the first number included in the confirmation response is being transferred, the loss of the data unit is A prohibition means for temporarily prohibiting the estimation by the disappearance estimation means;
Have
A communication system characterized by the above. Send machine, a transmission process of transmitting the data units of the transport layer to the receiver has an identifiable number the transmission order,
A receiving process in which a communication device receives the data unit transmitted by the transmitter;
A data transmission process in which the communication device stores in the first storage means that the data unit is being transferred in association with the received number of the data unit, and transmits the data unit to the receiver; ,
An acknowledgment reception process in which the communication device receives an acknowledgment including a first number which is a number of a data unit which is transmitted from the receiver to the transmitter and is expected to be received next by the receiver; ,
When the data unit received in the reception process and transmitted in the data transmission process is discarded, the communication device is associated with the number of the data unit and the data unit is discarded. An overwriting process stored in the first storage means for overwriting that the data unit is being transferred;
The communication device compares the first number included in the confirmation response received in the confirmation response reception process with the second number of the data unit stored in the second storage means;
When the second number is smaller than the first number, the first number is overwritten in the second storage means as the second number, and a data unit having a number smaller than the first number Is overwritten in the first storage means that it has been received at the receiver, and the confirmation response is transferred to the transmitter,
In the case where the second storage unit stores the fact that the data unit of the first number is discarded when the second number is not younger than the first number, the confirmation response is returned. When it is stored that the data unit of the first number is being transferred while the data unit of the first number is being transferred, the information including the information indicating that the data unit of the first number is being transferred An acknowledgment transmission process for transmitting an acknowledgment to the transmitter;
An erasure estimation process in which the transmitter estimates the erasure of the data units based on the order or timing of reception of the data units by the receiver;
When the transmitter includes information indicating that the data unit of the first number included in the confirmation response is being transferred in the confirmation response transmitted in the confirmation response transmission process , communication method and a stop step of temporarily disabled to estimate the loss of the data unit in the loss estimation process. A transmission process in which a transmitter transmits a transport layer data unit having a number capable of specifying a transmission order to a receiver;
A receiving process in which a communication device receives the data unit transmitted by the transmitter;
A data transmission process in which the communication device stores in the first storage means that the data unit is being transferred in association with the received number of the data unit, and transmits the data unit to the receiver; ,
An acknowledgment reception process in which the communication device receives an acknowledgment including a first number which is a number of a data unit which is transmitted from the receiver to the transmitter and is expected to be received next by the receiver; ,
When the data unit received in the reception process and transmitted in the data transmission process is discarded, the communication device is associated with the number of the data unit and the data unit is discarded. An overwriting process stored in the first storage means for overwriting that the data unit is being transferred;
The communication device is
Based on the first number included in the confirmation response received in the confirmation response reception process and the contents stored in a predetermined field of the confirmation response, a new reception confirmation is made by the confirmation response. In the case where a new reception confirmation is made by the confirmation response, it is determined that the data unit for which the new reception confirmation is made has been received by the receiver. Overwrite the storage means,
The predetermined field of the confirmation response stores a number larger than the third number which is the youngest number among the numbers of the data units stored as being transferred by the first storage means. If not, forward the acknowledgment to the transmitter,
When the predetermined field of the confirmation response stores a number larger than the third number, the number has a lower number than the number stored in the predetermined field and is received by the receiver A data unit that has not been overwritten in the first storage means is identified,
When it is stored in the first storage means that the specified data unit is discarded, the first field includes information indicating that the data unit is discarded, and the predetermined field includes the information The confirmation response storing the data unit number is transferred to the transmitter, while the first storage means stores that the identified data unit is being transferred, the data unit transfers An acknowledgment transmission process for transmitting to the transmitter the confirmation response including information indicating that the data unit is included and storing the number of the data unit in the predetermined field;
An erasure estimation process in which the transmitter estimates the erasure of the data units based on the order or timing of reception of the data units by the receiver;
When the transmitter includes information indicating that the data unit of the first number included in the confirmation response is being transferred in the confirmation response transmitted in the confirmation response transmission process, A suspension process temporarily prohibiting estimation of the loss of the data unit in the loss estimation process;
A communication method. The computer,
Data receiving means for receiving a transport layer data unit transmitted from a transmitter to a receiver and having a number capable of specifying a transmission order from the transmitter;
When the data unit is received by the data receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the receiver. Data transmission means for transmitting to,
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the data receiving unit and transmitted by the data transmitting unit is discarded, it is determined that the data unit is discarded in association with the number of the data unit. Overwrite means for overwriting that the data unit is being transferred, stored in the storage means,
Comparing the first number included in the confirmation response received by the confirmation response receiving means with the second number of the data unit stored in the second storage means;
When the second number is smaller than the first number, the first number is overwritten in the second storage means as the second number, and a data unit having a number smaller than the first number Is overwritten in the first storage means that it has been received at the receiver, and the confirmation response is transferred to the transmitter,
In the case where the second storage unit stores the fact that the data unit of the first number is discarded when the second number is not younger than the first number, the confirmation response is returned. When it is stored that the data unit of the first number is being transferred while the data unit of the first number is being transferred, the information including the information indicating that the data unit of the first number is being transferred A program for functioning as an acknowledgment transmission means for transmitting an acknowledgment to the transmitter . Computer
Data receiving means for receiving a transport layer data unit transmitted from a transmitter to a receiver and having a number capable of specifying a transmission order from the transmitter;
When the data unit is received by the data receiving means, the first storage means stores the data unit being transferred in association with the number of the data unit, and the data unit is stored in the receiver. Data transmission means for transmitting to,
An acknowledgment receiving means for receiving an acknowledgment that is transmitted from the receiver to the transmitter and that includes a first number that is a number of a data unit that is expected to be received next by the receiver;
When the data unit received by the data receiving unit and transmitted by the data transmitting unit is discarded, it is determined that the data unit is discarded in association with the number of the data unit. Overwrite means for overwriting that the data unit is being transferred, stored in the storage means,
Based on the first number included in the confirmation response received by the confirmation response receiving means and the content stored in a predetermined field of the confirmation response, a new reception confirmation is made by the confirmation response. In the case where a new reception confirmation is made by the confirmation response, it is determined that the data unit for which the new reception confirmation is made has been received by the receiver. Overwrite the storage means,
The predetermined field of the confirmation response stores a number larger than the third number which is the youngest number among the numbers of the data units stored as being transferred by the first storage means. If not, forward the acknowledgment to the transmitter,
When the predetermined field of the confirmation response stores a number larger than the third number, the number has a lower number than the number stored in the predetermined field and is received by the receiver A data unit that has not been overwritten in the first storage means is identified,
When it is stored in the first storage means that the specified data unit is discarded, the first field includes information indicating that the data unit is discarded, and the predetermined field includes the information The confirmation response storing the data unit number is transferred to the transmitter, while the first storage means stores that the identified data unit is being transferred, the data unit transfers An acknowledgment transmission means for transmitting to the transmitter the confirmation response including information indicating that the data is included and storing the number of the data unit in the predetermined field
Program to function as.

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