JP4973749B2 - Communication apparatus and communication control method - Google Patents

Description

  The present invention relates to a communication device and a communication control method.

  In packet communication in which data is converted into subdivided packets and transmitted, a multipath transmission method is usually employed. In the multipath transmission method, a technique for matching the transmission order of packets from a transmission source with the reception order of packets at a reception source has been developed.

  For example, the following Non-Patent Document 1 discloses a technology in which a router that distributes a series of packet flows routed to a multipath on a packet basis to a plurality of paths determines a path to be distributed according to an arrival interval of packets at the node. Thus, the arrival order of the packets at the receiving node is made the same as the packet transmission order of the transmitting node.

  Further, for example, Patent Document 1 below discloses a technique for quickly detecting a packet loss from a packet number at the head of a reception buffer in a multipath environment in which one session is transmitted using a plurality of paths. By requesting retransmission of a packet that is being transmitted, the arrival order of packets at the receiving node can be made the same as the packet transmission order of the transmitting node.

JP 2009-55419 A

“Dynamic Load Balancing Without Packet Reordering”, ACM SIGCOMM Computer Communication Review, June 2007

  However, even if packet transmission is controlled on the transmission side as in the technique described in Non-Patent Document 1, packets cannot always be received in order at the destination. This is because the use state of network resources changes from moment to moment, and therefore the delay time until arrival of a packet assumed at the time of transmission is not always correct. Further, depending on the network, the order may be changed due to the branching of the route in the middle of the route or the joining of the branched route again. In this case, it is difficult to control the arrival order guarantee on the transmission side.

  For example, a packet is transmitted every time one packet is received, and, for example, packets up to No. 10 are received under the control of requesting retransmission of a packet determined to be missing, and thereafter, as shown in FIG. Consider the case where packets are received on the receiving side in order. In this case, if it is not assumed that the order is reversed in the middle of the route, it is determined that the 11th and 12th packets are missing on the receiving side when the 13th packet arrives on the receiving side, The receiving side requests retransmission of the 11th and 12th packets.

  Also, consider a case where packets up to No. 20 are received under the same control, and then packets are received on the receiving side in the order shown in FIG. Also in this case, if it is not assumed that the order is reversed in the middle of the route, it is determined that the 21st to 26th packets are missing when the 27th packet arrives at the receiving side. No. packet is requested to be retransmitted.

  In this way, when a packet is transmitted by the multipath transmission method, if the order of the packets is switched by further branching the route along a certain route, it is placed at the head of the plurality of reception buffers of the receiving terminal. A packet loss is judged too early from a certain packet, and even a packet that is not actually lost is subject to retransmission.

  For example, consider a case where packets up to No. 20 are received, and then packets are received on the receiving side in the order shown in FIG. For example, suppose that the situation described in Patent Document 1, that is, packets sent from IF (interfaces) 1 and 2 of the transmitting terminal are received by IFs 3 and 4 of the receiving terminal. In this case, if the 27th packet is received by IF3 and the 26th packet is received by IF4 in the reception buffer, using the technique disclosed in Patent Document 2, the packet is transferred from the packet at the head of the reception buffer. Since it is determined whether the packet is lost, it is determined that the 21st to 25th packets are missing, and a retransmission of the 21st to 25th packets is requested from the receiving terminal.

  As described above, conventionally, even packets that are not actually lost are subject to retransmission, which increases the number of retransmissions of the packets and causes a problem that unnecessary traffic flows on the network.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to determine from a sequence of packets arriving at the reception side with respect to transmission packets assigned sequence numbers at the transmission side. By estimating the number of branches on the route, and even if the packet does not arrive as the sequence number on the receiving side, it is determined that order reversal has occurred based on the estimated number of branches, and the packet is retransmitted and delayed. It is an object of the present invention to provide a new and improved communication apparatus and communication control method capable of reducing the number of retransmissions.

  In order to solve the above-described problem, according to one aspect of the present invention, a receiving terminal that receives a packet in which a sequence of predetermined packets is assigned a sequence number from a transmitting terminal via a network is received by a receiving terminal. A packet receiving unit for receiving, an estimation unit for estimating and calculating the number of branches of the network path from the reception order of the packets received by the packet receiving unit, and missing in the middle of the route from the reception order and the number of branches A loss determination unit that determines a received packet; a packet holding unit that holds a packet received by the packet reception unit; a packet that is held in the packet holding unit; and an order of packets that are determined to be missing by the loss determination unit And a response unit that requests the transmitting terminal to retransmit the missing packet based on the number. It is.

  The estimation unit receives the packets up to the sequence number n (n is an integer equal to or greater than 0) and then receives all the packets of the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the largest sequence number received by the packet receiving unit until the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between packets of sequence number n + 1, in a column selected so that the number of sequence numbers in descending order is the maximum in the sequence in which the received packets are arranged in the order received by the packet receiver. The number of the order numbers arranged in descending order may be estimated as the number of branches of the route.

  After the packet receiving unit has received all the packets up to the order number n (n is an integer equal to or greater than 0), the missing determination unit is the mth greater than the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the maximum sequence number received by the packet receiving unit before the packet receiving unit receives all the packets from the sequence numbers n + 1 to m And for all received packets that fall between the packets of sequence number n + 1, the number estimated by the estimation unit is the number of the sequence numbers arranged in descending order in the sequence in which the received packets are arranged in the order received by the packet reception unit. If there is a packet whose number is greater than or equal to the number of branches in the route, the sequence number n + 1 is one prior to the smallest sequence number among the received packets that are greater than the sequence number n + 1. Packet may be determined to be missing at.

  The response unit receives a packet up to the sequence number n (n is an integer equal to or greater than 0) after the packet reception unit receives the packet, and the packet of the sequence number n + 1 is received even if the packet reception unit receives the packet. If the packet holding unit does not exist, a packet retransmission request may be withheld until the missing determination unit determines that the packet with the sequence number n + 1 is missing.

  In order to solve the above-described problem, according to another aspect of the present invention, a series of packets delimited by a predetermined number are transmitted from a transmission terminal with a sequence number and an interface identifier by a plurality of transmission interfaces via a network. In a receiving terminal that receives the received packet, a packet receiving unit that receives the packet, and an estimation unit that estimates and calculates the number of branches of the network path from the reception order of the packets received by the packet receiving unit and the interface identifier A loss determination unit that determines a packet that is lost during the route from the reception order, the interface identifier, and the number of branches, a packet holding unit that holds a packet received by the packet reception unit, and the packet holding unit And packets determined to be missing by the missing decision unit. And a Tsu preparative sequence number, and a response unit which requests the retransmission of the missing packets, characterized in that it comprises a communication device is provided.

  The estimation unit receives the packets up to the sequence number n (n is an integer equal to or greater than 0) and then receives all the packets of the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the largest sequence number received by the packet receiving unit until the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between the packets of sequence number n + 1, the sequence numbers are arranged in descending order in a sequence in which the received packets from a transmission interface are extracted from the received packets and arranged in the order received by the packet receiver. In the column selected so as to maximize the number, the number of the sequence numbers arranged in descending order may be estimated as the number of branches of the route in the transmission interface. .

  After the packet receiving unit has received all the packets up to the order number n (n is an integer equal to or greater than 0), the missing determination unit is the mth greater than the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the maximum sequence number received by the packet receiving unit before the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between the packet and the sequence number n + 1, the sequence number is descending in a sequence in which the received packets from a transmission interface are extracted from the received packets and arranged in the order received by the packet receiver. If the number of lines equal to or greater than the number of branches of the route estimated by the estimation unit is established for all transmission interfaces, the sequence number n + 1 Et al., It may be determined that packets up to one before the smallest sequence number among those larger than the sequence number n + 1 th of the received packet is missing.

  The response unit receives a packet up to the sequence number n (n is an integer equal to or greater than 0) after the packet reception unit receives the packet, and the packet of the sequence number n + 1 is received even if the packet reception unit receives the packet. If the packet holding unit does not exist, the packet retransmission request may be refrained until the missing determination unit determines that the packet with the sequence number n + 1 is missing.

  In order to solve the above-described problem, according to another aspect of the present invention, a packet receiving step of receiving a packet in which a sequence of predetermined packets is transmitted with a sequence number assigned from a transmitting terminal via a network. And an estimation step of estimating and calculating the number of branches of the network path from the reception order of the packets received in the packet reception step, and determining a packet lost in the middle of the path from the reception order and the number of branches Missing from the missing decision step, the packet holding step for holding the packet received in the packet receiving step, the packet held in the packet holding step and the sequence number of the packet determined to be missing in the missing decision step A response step for requesting the transmitting terminal to retransmit the received packet. The symptom, the communication control method is provided.

  In order to solve the above problem, according to another aspect of the present invention, a series of predetermined packets are transmitted from a transmission terminal via a network with a sequence number and an interface identifier assigned by a plurality of transmission interfaces. A packet receiving step for receiving received packets, an estimation step for estimating and calculating the number of branches of the network path from the reception order of the packets received in the packet receiving step and the interface identifier, the reception order, and the interface identifier And a loss determination step for determining a lost packet in the middle of the route from the number of branches, a packet holding step for holding a packet received in the packet receiving step, a packet held in the packet holding step, and the missing packet Judgment is missing in the judgment step And a is the order number of the packet, characterized in that it comprises a response requesting retransmission of missing packets, the communication control method is provided.

  As described above, according to the present invention, for a transmission packet to which a sequence number is assigned on the transmission side, the number of path branches is estimated from the sequence of packets that have arrived on the reception side, and packets are transmitted according to the sequence number on the reception side. Even if the packet has not arrived, it is possible to reduce the number of packet retransmissions by delaying the determination of the retransmission response by judging that the order reversal has occurred from the estimated number of branches. A communication apparatus and a communication control method can be provided.

It is explanatory drawing which shows schematic structure of the communication system which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the structure of the receiving terminal 100B concerning the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the estimation part 130 concerning the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the missing determination part 140 concerning the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the buffer 150 concerning the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the response part 170 concerning the 1st Embodiment of this invention. It is explanatory drawing which shows an example of the packet sequence which the receiving terminal 100B receives. It is explanatory drawing which shows an example of the packet sequence which the receiving terminal 100B receives. It is explanatory drawing which shows an example of the packet sequence which the receiving terminal 100B receives. 2 is an explanatory diagram showing an example of a route in the network 10. FIG. It is explanatory drawing which shows schematic structure of the communication system which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the structure of the receiving terminal 200B concerning the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the estimation part 230 concerning the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the missing determination part 240 concerning the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the buffer 250 concerning the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the response part 270 concerning the 2nd Embodiment of this invention. It is explanatory drawing which shows an example of the packet sequence which the receiving terminal 200B receives. It is explanatory drawing which shows an example of the packet sequence which the receiving terminal 200B receives. 2 is an explanatory diagram showing an example of a route in the network 10. FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. First Embodiment>
[1-1. Configuration of communication system]
First, a schematic configuration of a communication system according to the first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the communication system 1 according to the first embodiment of the present invention transmits a packet with a sequence number from the transmission terminal 100A to the reception terminal 100B via the network 10. Send the data you want. In the present embodiment, except for the case where the packet is retransmitted, the packet is transmitted in ascending order of the order number in principle.

  On the other hand, the receiving terminal 100B is an example of the communication device of the present invention, and when receiving a packet transmitted from the transmitting terminal 100A, the maximum number in a series of packets received without omission for the first time from the beginning of the sequence number, The number of the missing packet is transmitted as a response packet to the transmission terminal 100A. When the transmission terminal 100A receives this response packet, the transmission terminal 100A controls the sequence number of the next packet to be transmitted. Such communication control is found in communication systems such as TCP (Transmission Control Protocol). The present embodiment mainly relates to response packet control under such control.

  Inside the network 10 through which the packet flows, a route can be branched by a router (not shown) in the middle of the route distributing the packet to a plurality of routes. The branch shown in FIG. 1 represents the state. The transmitting terminal 100A and the receiving terminal 100B do not grasp the route or the number of branches through which the packet in the network 10 passes. In the following description, the network 10 is described as being branched into a plurality of paths. However, the present invention similarly applies even when there is no branch between the transmission terminal 100A and the reception terminal 100B. Applicable.

  The schematic configuration of the communication system according to the first embodiment of the present invention has been described above with reference to FIG. Next, the configuration of the receiving terminal 100B according to the first embodiment of the present invention will be described.

[1-2. Configuration of receiving terminal]
FIG. 2 is an explanatory diagram showing the configuration of the receiving terminal 100B according to the first embodiment of the present invention. Hereinafter, the configuration of the receiving terminal 100B according to the first embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 2, the receiving terminal 100B according to the first embodiment of the present invention includes a packet receiving unit 120, an estimation unit 130, a missing determination unit 140, a buffer 150, a data receiving unit 160, A response unit 170 and an information unit 180 are included.

  The packet receiving unit 120 receives a packet with an order number transmitted from the transmitting terminal 100A, and the packet receiving unit 120 passes the received packet to the buffer 150 in the order in which the packet is transmitted.

  The estimation unit 130 acquires the estimated value of the number of branches of the route held by the information unit 180 and the sequence number of the last packet received by the data reception unit 160, and estimates the sequence number and the number of branches. The number of branches along the transmission path is estimated from the value and the sequence of packets received by the packet receiving unit 120. The estimated number of branches estimated by the estimation unit 130 is sent to the information unit 180.

  In this embodiment, the number of branches in the middle of the transmission path is estimated as follows.

  The packet received by the packet receiving unit 120 is a packet transmitted from the transmitting terminal 100A to the receiving terminal 100B in ascending order of the sequence number. This is a state in which a packet with a small sequence number that has already been transmitted by the transmitting terminal 100A by a response packet from the receiving terminal 100B is not sent again. This is determined also by the receiving terminal 100B based on the response packet transmitted by itself.

  The estimation unit 130 acquires the estimated branch number k from the information unit 180 and also acquires the sequence number of the last packet received by the data reception unit 160. Assuming that the data reception unit 160 has received all the packets with the sequence numbers up to the nth (n = 0, 1, 2,...), When n = 0, the data reception unit 160 still does not receive the packet. I have not received. Thereafter, it is assumed that the packet receiving unit 120 receives an mth packet having an order number greater than the nth. When m−n ≦ k, the estimation unit 130 sets k as an estimated value of the number of branches. On the other hand, when m−n> k, the estimation unit 130 has received a packet selected from a packet having a larger sequence number than the nth received, including the previous mth packet. Arrange in order. Then, the estimation unit 130 counts up the number of the sequence numbers arranged in descending order for this packet sequence. However, the sequence numbers do not have to be consecutive. When there is one packet, the number is 1. For example, if the sequence numbers are aligned with 13 and 11, the number of sequence numbers arranged in descending order is 2, and if the sequence number is only 13, the number of sequence numbers arranged in descending order is 1.

  When m−n> k, the estimation unit 130 selects a packet sequence so that the number is maximized, and sets the number of the sequence numbers in this sequence in descending order as the estimated number of branches. Normally, packets arrive in ascending order of sequence numbers, but the arrival order of packets may be reversed due to a branch in the network 10. Therefore, in the present embodiment, the number in which the order numbers are arranged in descending order is estimated as the number of branches.

  The packets to be counted are the number with the largest sequence number received by the packet receiver 120 until the packet receiver 120 receives all the packets with the sequence numbers n + 1 to m + 1, and the n + 1th packet. All packets that fall in between (including the packet with the (n + 1) th sequence number). For example, when n = 10 and m = 13, it is assumed that the receiving terminal 100B receives packets in the order shown in FIG. In this case, the maximum number of packets received until the packet receiving unit 120 receives all the packets from n + 1 = 11 to m = 13, that is, the 11th and 12th packets is 16. . At this time, all packets that fall between No. 11 and No. 16, that is, Nos. 11, 12, 13, 14, 15, and 16, are counted. The maximum value of the number of the sequence numbers arranged in descending order is “3” in the case of 16, 15, 12 or 16, 15, 14.

  When the packet arrives at the receiving terminal 100B as shown in FIG. 7, the packet is transferred from the transmitting terminal 100A to the receiving terminal 100B through the route shown in FIG. 10, for example. In this case, the estimated value of the number of branches is “3”.

  The missing determination unit 140 includes the sequence of packets received by the packet reception unit 120, the last sequence number received by the data reception unit 160, which is held by the information unit 180, and the information unit 180. From the estimated value k of the number of branches, it is determined whether the packet has not arrived or is missing along the route. When determining that the packet is missing, the missing determination unit 140 notifies the response unit 170 of the sequence number of the missing packet.

  A packet loss determination method by the loss determination unit 140 will be described below.

  It is assumed that the last sequence number received by the data receiving unit 160 held by the information unit 180 is the nth (n = 0, 1, 2,...). Next, when the packet receiving unit 120 receives the m-th packet having an order number greater than the (n + 1) th, the missing determination unit 140 selects the packet including the packet and having a larger order number than the (n + 1) th order received thereafter. The packets are arranged in the order received by the packet receiving unit 120. Then, the number of sequence numbers arranged in descending order is counted for this packet sequence. However, the sequence numbers do not have to be consecutive. If there is a packet sequence in which this number is greater than or equal to k, the drop determination unit 140 drops the packets from the (n + 1) th to the one before the smallest sequence number among the numbers larger than the (n + 1) th received so far. It is determined that

  The buffer 150 receives packets from the packet receiving unit 120, and the packets received by the buffer 150 are sent to the data receiving unit 160 without duplication in ascending order of sequence numbers. Further, the last number of the sequence numbers sent to the data receiving unit 160 is sent from the buffer 150 to the information unit 180. If the packet received from the packet receiving unit 120 overlaps with a packet existing in the buffer 150 or is the same as the packet already sent to the data receiving unit 160, the packet is discarded from the buffer 150. The

  The data receiving unit 160 receives a packet passed from the buffer 150.

  The response unit 170 generates and transmits a response packet for controlling the number and number of packets sent by the transmission terminal 100A. In order to transmit the response packet, the response unit 170 acquires the last sequence number n received by the data reception unit 160 from the information unit 180. The response unit 170 also acquires information on the missing packet from the missing determination unit 140.

  The content of the response packet generated by the response unit 170 may be (1) information indicating which sequence number packet is received in the correct order, and (2) requesting retransmission of a packet with a specific sequence number. It may be. Regardless of the content of the packet, the transmitting terminal 100A that has received the response packet knows which packet has not been sent to the receiving terminal 100B, and the transmitting terminal 100A retransmits the packet to be delivered to the receiving terminal 100B. I can do it.

  The response packet from the receiving terminal 100B describes at least one of the contents of (1) or (2) at a predetermined control timing between the transmitting terminal 100A and the receiving terminal 100B. The data is transmitted from the receiving terminal 100B to the transmitting terminal 100A.

  When it is time to send a response packet, when there is no packet in buffer 150, response unit 170 transmits the response packet according to at least one of the above-described (1) and (2). On the other hand, when it is time to send the response packet, the response unit 170 has a packet in the buffer 150, that is, the packet does not reach the sequence number, and there is a packet with the missing sequence number. When there is a packet, even if the contents of (1) or (2) are transmitted, the response packet is not transmitted until the missing sequence number is received from the missing determination unit 140. However, in the case of (2), the response unit 170 may transmit the response packet on the assumption that there is no missing packet, that is, the content not requesting retransmission of the missing packet. Thereafter, if there is a packet loss notification from the loss determination unit 140, the response unit 170 notifies the transmission terminal 100A of the packet loss.

  The information unit 180 stores the estimated branch number estimated by the estimation unit 130 and the last sequence number of the packets sent from the buffer 150 to the data reception unit 160. The initial value of the estimated value of the number of branches of the route stored in the information unit 180 is 1. The last sequence number guarantees that the data reception unit 160 has received all packets with sequence numbers before this number.

  The configuration of the receiving terminal 100B according to the first embodiment of the present invention has been described above using FIG. Next, the operation of the receiving terminal 100B according to the first embodiment of the present invention will be described.

[1-3. Operation of receiving terminal]
As described above, the packet receiving unit 120 receives a packet with an order number transmitted from the transmitting terminal 100A, and passes the received packet to the buffer 150 in the order received.

  FIG. 3 is a flowchart showing the operation of the estimation unit 130 included in the receiving terminal 100B according to the first embodiment of the present invention. Hereinafter, the operation of the estimation unit 130 will be described in detail with reference to FIG.

  It is assumed that the packet received by the packet receiving unit 120 is a packet transmitted from the transmitting terminal 100A to the receiving terminal 100B in ascending order of the sequence number. The estimation unit 130 acquires the estimated value k of the number of branches from the information unit 180 and also acquires the sequence number n of the last packet received by the data reception unit 160 (step S301).

  Subsequently, the estimating unit 130 acquires the sequence number m of the packet newly received by the packet receiving unit 120 (step S302). The estimation unit 130 determines whether or not mn ≦ k is satisfied (step S303). If mn ≦ k, the process proceeds to the subsequent step S308. If k <mn, the estimation unit 130 is determined. Acquires the sequence number of the packet received by the packet receiving unit 120 after the packet with the sequence number m (step S304).

  Subsequently, the estimation unit 130 arranges the packets selected from the packets having the order number larger than the order number n, including the packet with the order number m, in the order received by the packet reception unit 120. For the column, the number d in which the sequence numbers are arranged in descending order is counted (step S305). The packet to be counted includes the packet having the largest sequence number received by the packet receiving unit 120 until the packet receiving unit 120 receives all the packets having the sequence numbers n + 1 to m. All packets that fall between the packets of number n + 1. The estimation unit 130 uses the number d in which the sequence numbers are arranged in descending order for the packet sequence selected so that the number is maximized as candidates for the estimated number of branches.

  The estimation unit 130 uses the number d in which the sequence numbers are arranged in descending order as candidates for the estimated number k of branch numbers for the packet sequence selected so that the number in which the sequence numbers are arranged in descending order is the maximum counted in step S305. (Step S306). Then, the estimation unit 130 determines that the packet having the largest sequence number received by the packet reception unit 120 and the sequence number of all packets having the sequence numbers n + 1 to m are received by the packet reception unit 120. It is determined whether all the packets that fall between the n + 1th packet have been received (step S307). If all the packets have been received, the estimating unit 130 stores the estimated number k of the number of branches determined as a candidate in step S306 in the information unit 180 (step S308). On the other hand, if all the packets have not been received yet, the process returns to step S304, and the estimation unit 130 further executes processing for obtaining the sequence number of the next received packet.

  Thus, the estimation unit 130 can estimate the number of branches in the network 10. The receiving terminal 100B can determine whether or not a packet is missing using the number of branches estimated by the estimation unit 130.

  The operation of the estimation unit 130 has been described in detail with reference to FIG. Next, the operation of the missing determination unit 140 included in the receiving terminal 100B according to the first embodiment of the present invention will be described.

  FIG. 4 is a flowchart showing the operation of the missing determination unit 140 included in the receiving terminal 100B according to the first embodiment of the present invention. Hereinafter, the operation of the missing determination unit 140 will be described in detail with reference to FIG.

  First, at the time of packet loss determination processing, the loss determination unit 140 acquires an estimated value k of the number of branches and the sequence number n of the last packet received by the data reception unit 160 from the information unit 180 (step S401). . Next, the loss determination unit 140 receives the sequence number m of the packet newly received by the packet reception unit 120 (step S402), and determines whether n + 1 <m is satisfied (step S403).

  If n + 1 ≧ m is determined as a result of the determination in step S403, the loss determination unit 140 determines that no loss has occurred in the received packet, and ends the process. On the other hand, if n + 1 <m is determined as a result of the determination in step S403, the missing determination unit 140 determines whether k = 1 (step S404).

  As a result of the determination in step S404, when the value of the number of branches k held in the information unit 180 is k = 1, it is determined that the received packet is missing, and the missing determination unit 140 The packet 170 is notified to the unit 170 (step S405). In this step S405, the loss determination unit 140 determines that the packet of the sequence number from the (n + 1) th to the one before the smallest sequence number among the numbers greater than the (n + 1) th received so far is missing, Notify the response unit 170 of the missing packet.

  On the other hand, as a result of the determination in step S404, if the value of the number of branches k held in the information unit 180 is not k = 1, the missing determination unit 140 then receives the packet received next by the packet reception unit 120. Is obtained (step S406).

  When the packet reception unit 120 acquires the sequence number of the next packet received in step S406, the missing determination unit 140 determines whether the sequence number acquired in step S406 is n + 1 (step S407). .

  As a result of the determination in step S407, if the sequence number acquired in step S406 is n + 1, the lack determination unit 140 ends the process. On the other hand, as a result of the determination in step S407, if the sequence number acquired in step S406 is not n + 1, the missing determination unit 140 subsequently received from the packet reception unit 120 including the packet with the sequence number m. The sequence number selected from the sequence numbers greater than n + 1 in the order received by the packet receiving unit 120 is counted, and the number d of sequence numbers starting from a certain number in descending order is counted (step S408).

  Then, the missing determination unit 140 determines whether there is a column satisfying k ≦ d for the number d counted in step S408 (step S409). If there is even one column that satisfies k ≦ d, it is determined that the received packet is missing, and the missing determination unit 140 notifies the response unit 170 of the missing packet (step S405). On the other hand, if d <k for d in any column, the process returns to step S406, and the loss determination unit 140 acquires the sequence number of the next packet received by the packet reception unit 120.

  The operation of the missing determination unit 140 has been described in detail above with reference to FIG. Next, the operation of the buffer 150 included in the receiving terminal 100B according to the first embodiment of the present invention will be described.

  FIG. 5 is a flowchart for explaining the operation of the buffer 150 included in the receiving terminal 100B according to the first embodiment of the present invention. Hereinafter, the operation of the buffer 150 will be described with reference to FIG.

  First, when the buffer 150 receives a packet from the packet receiving unit 120 (step S501), the buffer 150 passes the received packet to the data receiving unit 160 in order from the smallest sequence number assigned to the received packet (step S502). If there is a packet with the missing sequence number, the buffer 150 waits until the packet is sent from the packet receiving unit 120. In addition, if there is a packet that has already been duplicated to the data receiving unit 160, the buffer 150 discards the packet.

  Then, the buffer 150 passes the sequence number of the last packet passed to the data receiving unit 160 to the information unit 180.

  The operation of the buffer 150 has been described above with reference to FIG. Next, the operation of the response unit 170 included in the receiving terminal 100B according to the first embodiment of the present invention will be described.

  FIG. 6 is a flowchart showing the operation of the response unit 170 according to the first embodiment of the present invention. The operation of the response unit 170 according to the first embodiment will be described below using FIG.

  The response unit 170 acquires the sequence number n of the last packet received by the data reception unit 160 from the information unit 180 (step S601). Next, the response unit 170 checks whether a packet exists in the buffer 150 (step S602).

  As a result of the confirmation in the step S602, if there is no packet in the buffer 150 or if there is a packet whose sequence number is n + 1, the packet can be received according to the sequence number. A response packet is transmitted with at least one of the contents of (1) or (2), and the process is terminated.

  On the other hand, as a result of the confirmation in step S602, if there is a packet with the sequence number n + 2 or later in the buffer 150, has the response unit 170 received a notification of the deletion of the packet with the sequence number n + 1 from the loss determination unit 140? Whether or not is confirmed (step S603). If the notification of the loss of the packet with the sequence number n + 1 is not received from the loss determination unit 140, the process returns to step S602, and the response unit 170 refrains from transmitting the response packet. On the other hand, if the notification of the loss of the packet with the sequence number n + 1 is received from the loss determination unit 140, the response unit 170 informs the transmitting terminal 100A that the packet with the sequence number n + 1 is missing. Notification is made (step S604). This notification is performed according to at least one of the above-described (1) and (2).

  The operation of the response unit 170 according to the first embodiment has been described above with reference to FIG. As described above, the response unit 170 refrains from transmitting a response packet until it receives a notification of the loss of the packet with the sequence number n + 1 from the loss determination unit 140, thereby suppressing generation of useless traffic to the network 10.

  Here, specific operation examples of the estimation unit 130, the loss determination unit 140, the buffer 150, and the response unit 170 will be described. The transmitting terminal 100A transmits, to the receiving terminal 100B, data packets assigned with sequence numbers that follow 1, 2, 3,. Hereinafter, when there is a description about the packet number, this sequence number is indicated unless otherwise specified. Assume that the receiving terminal 100B receives the data packet transmitted by the transmitting terminal 100A and transmits one response packet to the transmitting terminal 100A every time one packet is received.

  There is a possibility that both a data packet transmitted from the transmitting terminal 100A and a response packet transmitted from the receiving terminal 100B are distributed to a plurality of paths by a router (not shown) or the like in the network 10 along the path. However, neither the transmission terminal 100A nor the reception terminal 100B knows how many routes are distributed.

  Here, it is assumed that the receiving terminal 100B has received data packets in order up to No. 10, and has received all the packets received by the data receiving unit 160. Hereinafter, the operation of the receiving terminal 100B regarding the packet received from the transmitting terminal 100A will be specifically described with reference to the drawings. At this time, the information unit 180 stores the last sequence number 10 received by the data receiving unit 160 and the estimated value k = 1 of the branch number of the route.

  At this time, it is assumed that the packet receiving unit 120 receives the 13th packet. The 13th packet received by the packet receiving unit 120 is passed to the buffer 150. Then, when the packet receiving unit 120 receives the packets in the order shown in FIG. 7 including the 13th packet, the operation of the estimating unit 130 will be described with reference to the flowchart shown in FIG.

  First, the estimation unit 130 acquires the estimated value k = 1 of the number of branches from the information unit 180, and acquires the sequence number n = 10 of the last packet received by the data reception unit 160 (step S301). Subsequently, the estimating unit 130 acquires the sequence number m = 13 of the packet newly received by the packet receiving unit 120 (step S302). The estimation unit 130 determines whether or not m−n ≦ k is satisfied (step S303). Since k <mn, the estimation unit 130 determines that the packet reception unit 120 follows the packet with the sequence number m = 13. The sequence number (11) of the received packet is acquired (step S304).

  When the 11th packet is received, the numbers arranged in descending order are the 13th and 11th, which is two. Therefore, the number d in which the sequence numbers are arranged in descending order is d = 2 (step S305). Then, the estimation unit 130 sets the number d = 2 in which the order numbers are arranged in descending order as candidates for the estimated number k of branch numbers (step S306).

  The maximum sequence number when the 11th packet is received is 13. Since the packet receiving unit 120 has not received the 12th packet, the estimating unit 130 receives the packet with the largest sequence number (the 13th packet) received by the packet receiving unit 120 and the packet with the n + 1 sequence number. It is determined whether or not all packets that fall between (No. 11) have been received (step S307), and since all the packets have not been received, the process returns to step S304, and the estimation unit 130 further A process for obtaining the sequence number of the received packet is executed.

  After that, when the packet receiving unit 120 receives the 14th packet, the numbers arranged in descending order are the 16th, 15th, and 14th when the 14th packet is received. Accordingly, the number d in which the sequence numbers are arranged in descending order is d = 3 (step S305). Then, the estimating unit 130 sets the number d = 3 in which the order numbers are arranged in descending order as candidates for the estimated number k of branch numbers (step S306).

  The maximum sequence number when the 14th packet is received is 16. Whether the estimation unit 130 has received all packets received between the packet with the largest sequence number (16th packet) received by the packet receiving unit 120 and the packet with the sequence number n + 1 (11) Since all packets have been received, the estimation unit 130 stores the estimated number k = 3 of the number of branches determined as a candidate in step S306 in the information unit 180 (step S308).

  The estimated number of branches is 1 until the estimation unit 130 estimates the estimated number of branches as 3. The operation of the buffer 150 when the estimated value of the number of branches is 1 and up to the 15th packet is received as shown in FIG. 8 will be described with reference to the flowchart shown in FIG.

  When the buffer 150 receives a packet from the packet receiving unit 120 (step S501), it passes the eleventh packet to the data receiving unit 160 in ascending order of the sequence number given to the received packet (step S502) and the buffer. 150 passes the sequence number (11) of the last packet passed to the data receiving unit 160 to the information unit 180. At this time, the 13th, 16th, and 15th packets are still held in the buffer 150.

  Further, as shown in FIG. 8, when the 13th packet is received and the 13th packet is stored in the buffer 150, the operations of the missing determination unit 140 and the response unit 170 are shown in the flowcharts shown in FIGS. It explains along.

  In the packet loss determination process, the loss determination unit 140 acquires, from the information unit 180, the estimated number of branches k = 1 and the sequence number n = 10 of the last packet received by the data reception unit 160 (step S1). S401). Next, the drop determination unit 140 receives the sequence number m = 13 of the packet newly received by the packet reception unit 120 (step S402), and since n + 1 <m and k = 1, there is a drop in the received packet. It is determined that the packet has occurred, and the loss determination unit 140 notifies the response unit 170 of the loss of the 11th and 12th packets (step S405).

  When the receiving terminal 100B receives the 13th packet, the response unit 170 acquires the sequence number n = 10 of the last packet received by the data receiving unit 160 from the information unit 180 (step S601). Next, the response unit 170 checks whether or not there is a packet in the buffer 150 (step S602). Since the 13th packet exists in the buffer 150, the response unit 170 determines the sequence number from the missing determination unit 140. It is confirmed whether or not notification of the loss of the 11th and 12th packets has been received (step S603). If the notification of the loss of the packets with the sequence numbers 11 and 12 is received from the loss determination unit 140, the response unit 170 has lost the packets with the sequence numbers 11 and 12 from the transmitting terminal 100A. This is notified by a response packet (step S604).

  On the other hand, the operations of the drop determination unit 140, the buffer 150, and the response unit 170 when the estimation unit 130 receives up to the packet in the order shown in FIG. 4, and will be described along the flowcharts shown in FIGS. When the packet is received in the order as shown in FIG. 9, the information unit 180 includes the last sequence number 20 received by the data receiving unit 160 and the estimated value k = 3 is stored.

  In the packet loss determination process, the loss determination unit 140 acquires, from the information unit 180, the estimated number k of branches = 3 and the sequence number n = 20 of the last packet received by the data reception unit 160 (Step S1). S401). Next, the loss determination unit 140 receives the sequence number m = 23 of the packet newly received by the packet reception unit 120 (step S402). Since n + 1 <m and k = 1 is not satisfied, next, the loss determination unit 140 acquires the sequence number (26) of the next packet received by the packet receiver 120 (step S406).

  When the packet reception unit 120 acquires the sequence number of the next packet received in step S406, the missing determination unit 140 determines whether the sequence number acquired in step S406 is n + 1 (21) (step S406). S407). Since the sequence number acquired in step S406 is not n + 1 (21), the loss determination unit 140 subsequently includes a packet with sequence number m = 23, and the sequence greater than n + 1 (21) received from the packet receiver 120 so far. For a column in which the sequence numbers selected from the numbers are arranged in the order received by the packet receiving unit 120, the number d starting from a certain number and arranged in descending order is counted (step S408). Since the number d is 1 and d <k, the process returns to step S406, and the loss determination unit 140 acquires the sequence number (25) of the next packet received by the packet reception unit 120.

  Since the sequence number acquired in step S406 is not n + 1 (21), the number d of the sequence numbers arranged in descending order is counted again. Since d = 2 and d <k, the process returns to step S406 again, and the packet receiving unit 120 acquires the sequence number (21) of the next received packet. Since this sequence number is equal to n + 1, the lack determination unit 140 ends the process.

  When the buffer 150 receives the 21st packet from the packet receiving unit 120 (step S501), the buffer 150 passes the received 21st packet to the data receiving unit 160 (step S502), and the buffer 150 passes to the data receiving unit 160. The sequence number (21) of the last packet is passed to the information unit 180. At this time, the 23rd, 26th, and 25th packets are still held in the buffer 150.

  In addition, the response unit 170 acquires the sequence number n = 20 of the last packet received by the data reception unit 160 from the information unit 180 (step S601). Next, the response unit 170 confirms whether or not there is a packet in the buffer 150 (step S602). Since there are only packets of the number n + 1 (21) and later in the buffer 150, the response unit 170 determines whether there is a missing packet. It is confirmed whether or not the notification of the loss of the packet with the sequence number n + 1 (21) is received from the unit 140 (step S603). If the notification of the loss of the packet with the sequence number n + 1 (21) is not received from the loss determination unit 140, the process returns to step S602, and the response unit 170 refrains from transmitting the response packet.

  Eventually, when the packet No. 21 arrives at the buffer 150, the packet was received according to the sequence number. Therefore, the response unit 170 responds with a predetermined content (1) or (2). Is transmitted to the transmitting terminal 100A, and the process is terminated.

  Heretofore, specific operation examples of the estimation unit 130, the missing determination unit 140, the buffer 150, and the response unit 170 have been described.

  As described above, according to the receiving terminal 100B according to the first embodiment of the present invention, the estimation unit 130 estimates the number of branches in the network 10 from the sequence number of the packet received by the packet receiving unit 120. Even when the packet is not received according to the number, transmission of the response packet from the response unit 170 is refrained using the information on the number of branches. As a result, the receiving terminal 100B does not erroneously determine that the packet loss is in the middle of the route even when the packet arrival order is reversed due to the branch in the middle of the communication route.

  In the prior art, the arrival order is not guaranteed by branching in the middle of the route, so when a packet with a larger order number arrives first at the receiving terminal, a packet with a smaller order number is automatically determined to be a packet loss, and the response The packet causes retransmission from the transmitting terminal. For example, as described above, in the prior art, when a packet arrives as shown in FIG. 7, the 11th and 12th packets are to be retransmitted when the 13th packet arrives. On the other hand, since the receiving terminal 100B according to the first embodiment of the present invention determines whether or not a packet has arrived from a packet that arrives later, the 11th and 12th packets are immediately received when the 13th packet arrives. No. packet is not subject to retransmission. Therefore, according to the first embodiment of the present invention, even when a packet does not arrive according to the number, it is not determined whether a packet has arrived at the time of arrival of the packet, but is also determined from a packet that arrives later. Therefore, it is possible to prevent unnecessary traffic from flowing through the network.

<2. Second Embodiment>
[2-1. Configuration of communication system]
Next, a schematic configuration of a communication system according to the second embodiment of the present invention will be described with reference to FIG. As shown in FIG. 11, the communication system 2 according to the second embodiment of the present invention transmits a packet with a sequence number from the transmission terminal 200A to the reception terminal 200B via the network 10. Send the data you want. In the present embodiment, except for the case where the packet is retransmitted, the packet is transmitted in ascending order of the order number in principle.

  The transmission terminal 200A has a plurality of (for example, two) interfaces IF1 and IF2, and distributes packets to be transmitted to the interfaces IF1 and IF2. The packet is provided with a mark (IF number) for distinguishing a plurality of interfaces, and there is no particular rule as to which packet is assigned to which interface.

  On the other hand, when receiving terminal 200B receives the packet transmitted from transmitting terminal 200A, it starts from the beginning of the sequence number and receives the maximum number in the series of packets received without omission or the number of the missing packet. It transmits to the transmission terminal 200A as a response packet. When the transmission terminal 200A receives this response packet, the transmission terminal 200A can control the packet to be transmitted next. Such communication control is found in communication systems such as TCP. Similarly, this embodiment mainly relates to control of response packets under such control.

  Inside the network 10 through which the packet flows, a route can be branched by a router (not shown) in the middle of the route distributing the packet to a plurality of routes. The branch shown in FIG. 11 represents the state. The transmitting terminal 200A and the receiving terminal 200B do not grasp the route or the number of branches through which the packet in the network 10 passes. In the following description, the network 10 is described as being branched into a plurality of paths. However, the present invention similarly applies even when there is no branch between the transmission terminal 100A and the reception terminal 100B. Applicable.

  The schematic configuration of the communication system according to the second embodiment of the present invention has been described above with reference to FIG. Next, the configuration of the receiving terminal 200B according to the second embodiment of the present invention will be described.

[2-2. Configuration of receiving terminal]
FIG. 12 is an explanatory diagram showing the configuration of the receiving terminal 200B according to the second embodiment of the present invention. Hereinafter, the configuration of the receiving terminal 200B according to the second embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 12, the receiving terminal 200B according to the second embodiment of the present invention includes a packet receiving unit 220, an estimating unit 230, a missing determination unit 240, a buffer 250, a data receiving unit 260, A response unit 270 and an information unit 280 are included.

  The packet receiving unit 220 receives a packet with an order number and an IF number transmitted from the transmitting terminal 200A, and the packet receiving unit 120 receives the received packet in the buffer 150 in the order in which the packet was transmitted. To pass. In the present embodiment, it is assumed that either IF number 1 or 2 is assigned to the packet.

  When the transmission terminal 200A receives the number of interfaces used when transmitting data to the reception terminal 200B, the estimated value of the number of branches of each interface is passed to the information unit 280 with an initial value of 1. The number of interfaces may be any number as long as the number of interfaces of the packet transmitted by the transmission terminal 200A can be determined, such as an interface identifier. The number of interfaces may be determined from the type of mark given to the packet by the transmitting terminal 200A. In the present embodiment, the receiving terminal 200B receives the number of interfaces from the transmitting terminal 200A.

  The estimation unit 230 acquires an estimated value of the number of branches of the path for each interface held by the information unit 280 and the sequence number of the last packet received by the data reception unit 260, and the sequence number and the interface The number of branches in the transmission path is estimated from the estimated value of the number of branches for each packet and the sequence of packets received by the packet receiver 220. The estimated number of branches estimated by the estimation unit 230 is sent to the information unit 280.

  In this embodiment, the number of branches in the middle of the transmission path is estimated as follows.

  The packet received by the packet receiving unit 220 is a packet transmitted from the transmitting terminal 200A to the receiving terminal 200B in ascending order of the sequence number. This is a state in which a packet with a small sequence number that has already been transmitted by the transmitting terminal 200A by a response packet from the receiving terminal 200B is not sent again. This is determined also by the receiving terminal 200B based on the response packet transmitted by itself.

The estimation unit 230 acquires the branch number estimation value k _i from the information unit 280 and also acquires the sequence number of the last packet received by the data reception unit 160. Note that the subscript i is an identifier for distinguishing interfaces, and the subscript is used in the same meaning in the following. Assuming that the data receiving unit 260 has received all the packets with sequence numbers up to the nth (n = 0, 1, 2,...), If n = 0, the data receiving unit 260 still does not receive the packet. I have not received. Thereafter, it is assumed that the packet receiving unit 220 receives the m-th packet whose order number is greater than the n-th. This is a packet from IFi of the transmission terminal 200A. When m−n ≦ k _i , the estimation unit 230 sets k _i as an estimated value of the number of branches in the interface IFi. On the other hand, if m-n> k _i, estimating section 230, the including previous m-th packet, selected from n-th sequence number packets larger than that subsequently received for each interface packet, the packet receiving unit 220 are arranged in the order received. Then, the estimation unit 230 counts the number of the sequence numbers arranged in descending order for this packet sequence. However, the sequence numbers do not have to be consecutive. When there is one packet, the number is 1. For example, if the sequence numbers are aligned with 13 and 11, the number of sequence numbers arranged in descending order is 2, and if the sequence number is only 13, the number of sequence numbers arranged in descending order is 1.

  When m−n> k, the estimation unit 230 selects a packet sequence so that this number is maximized for each interface, and estimates the number of branches of the interface by the number of the sequence numbers in the descending order. Value. Normally, packets arrive in ascending order of sequence numbers, but the arrival order of packets may be reversed due to a branch in the network 10. Therefore, in the present embodiment, the number in which the order numbers are arranged in descending order is estimated as the number of branches.

The packets to be counted are the number with the largest sequence number received by the packet receiver 220 and the n + 1th packet until the packet receiver 220 receives all the packets with the sequence numbers n + 1 to m + 1. All packets that fall in between (including the packet with the (n + 1) th sequence number). For example, when n = 10 and m = 13, it is assumed that the receiving terminal 200B receives the packets in the order shown in FIG. In this case, the maximum number of packets received until the packet receiving unit 220 receives all the packets from n + 1 = 11 to m = 13, that is, the 11th and 12th packets is 16. . At this time, all packets that fall between No. 11 and No. 16, that is, Nos. 11, 12, 13, 14, 15, and 16, are counted. The maximum value of the numbers in which the sequence numbers are arranged in descending order is “3” when IF1 is 16, 15, and 14, and is “2” when IF2 is 12 and 11. Therefore, the estimated number of branches is k ₁ = 3 and k ₂ = 2.

  When the packet reaches the receiving terminal 200B as shown in FIG. 17, for example, the packet is transferred from the transmitting terminal 200A to the receiving terminal 200B through the route shown in FIG.

The missing determination unit 240 includes the sequence of packets received by the packet receiving unit 220, the last sequence number received by the data receiving unit 260, which is held by the information unit 280, and the information unit 280. From the estimated number k _{i of the} number of branches for each interface, it is determined whether the packet has not arrived or is missing along the route. If the missing determination unit 240 determines that the packet is missing, the missing determination unit 240 notifies the response unit 270 of the sequence number of the missing packet.

  A packet loss determination method by the loss determination unit 240 will be described below.

  Assume that the last sequence number received by the data receiving unit 260 and held by the information unit 280 is the nth (n = 0, 1, 2,...). Next, when the packet receiving unit 220 receives the m-th packet having an order number greater than the (n + 1) th, the missing determination unit 240 selects the packet including the packet and having a larger order number than the (n + 1) th received thereafter. The packets are arranged in the order received by the packet receiving unit 220. Then, from this packet sequence, packets are selected for each interface as they are arranged, and the number of sequence numbers in descending order for the packet sequence selected for each interface is counted for each interface. However, the sequence numbers do not have to be consecutive. If there is one packet, the number is 1.

Then, for each interface, the missing determination unit 240 checks whether the packet of the interface has a packet sequence in which the number of the sequence numbers arranged in descending order is equal to or more than the estimated number k _{i of} branch numbers. If all the interfaces satisfy this condition, the missing determination unit 140 is missing packets from the (n + 1) th to the one before the smallest sequence number among the numbers larger than the (n + 1) th received so far. Is determined.

  The buffer 250 receives packets from the packet receiver 220, and the packets received by the buffer 250 are sent to the data receiver 260 without duplication in ascending order of the sequence numbers. Also, the last number of the sequence number sent to the data receiving unit 260 is sent from the buffer 250 to the information unit 280. If a packet received from the packet receiving unit 220 overlaps with a packet existing in the buffer 250 or is the same packet already sent to the data receiving unit 260, the packet is discarded from the buffer 250. The

  The data receiving unit 260 receives a packet passed from the buffer 250.

  The response unit 270 generates and transmits a response packet for controlling the number and number of packets sent by the transmission terminal 200A. In order to transmit the response packet, the response unit 270 obtains the last sequence number n received by the data receiving unit 260 from the information unit 280. The response unit 270 also acquires information on the missing packet from the missing determination unit 240.

  The response unit 270 has the same function as the response unit 170 in the first embodiment of the present invention described above. That is, when it is time to send a response packet, if there is no packet in the buffer 250, the response packet is transmitted with at least one of the above-described contents (1) and (2). On the other hand, when it is time to send a response packet, the response unit 270 receives a packet in the buffer 250, that is, the packet has not arrived according to the sequence number, and there is a packet with the missing sequence number. When there is a packet, even if the contents of (1) or (2) are transmitted, the response packet is not transmitted until the missing sequence number is received from the missing determination unit 140. However, in the case of (2) above, the response unit 270 may transmit the response packet on the assumption that there is no missing packet, that is, the content not requesting retransmission of the missing packet.

The information unit 280 estimates the estimated branch number k _i of the path for each interface used for packet transmission of the transmission terminal 200A estimated by the estimation unit 230 and the last of the packets sent by the buffer 250 to the data reception unit 260. Save the order number. The initial value of the estimated value k _i of the branch number of the route stored in the information unit 280 is 1. The last sequence number guarantees that the data reception unit 260 has received all packets with sequence numbers before this number.

  The configuration of the receiving terminal 200B according to the second embodiment of the present invention has been described above using FIG. Next, the operation of the receiving terminal 200B according to the second embodiment of the present invention will be described.

[2-3. Operation of receiving terminal]
As described above, the packet receiving unit 220 receives the packet with the sequence number and the IF number transmitted from the transmission terminal 200A, and passes the received packet to the buffer 250 in the transmitted sequence. Further, when the receiving terminal 200B receives the number of interfaces used when the transmitting terminal 200A transmits data to the receiving terminal 200B, the initial value of the estimated number k _i of the branch number of each interface is set to 1 and passed to the information unit 280. .

  FIG. 13 is a flowchart showing the operation of the estimation unit 230 included in the reception terminal 200B according to the second embodiment of the present invention. Hereinafter, the operation of the estimation unit 230 will be described in detail with reference to FIG.

As a premise, the packet received by the packet receiving unit 220 is a packet transmitted from the transmitting terminal 200A to the receiving terminal 200B in ascending order of the sequence number. The estimation unit 230 obtains the estimated number k _{i of the} number of branches of each interface from the information unit 280, and obtains the sequence number n of the last packet received by the data reception unit 260 (step S1301).

Subsequently, the estimating unit 230 acquires the sequence number m of the packet newly received by the packet receiving unit 220 and the IF number i of the packet (step S1302). Estimating unit 230 determines whether the m-n ≦ _{k i} (step S1303), if m-n ≦ _{k i} proceeds to the subsequent step _S1308, if k i <m-n, The estimation unit 230 acquires the sequence number of the packet received by the packet reception unit 220 next to the packet with the sequence number m and the IF number i of the packet (step S1304).

Subsequently, the estimation unit 230 arranges the packets selected from the packets having the order number larger than the order number n, including the packet with the order number m, in the order received by the packet reception unit 220. From the column, the packet is selected for each interface with the arrangement. Then, for the packet sequence selected for each interface, the number d _{i in} which the sequence numbers are arranged in descending order for each interface is counted up (step S1305). However, the sequence numbers do not have to be consecutive, and when there is one packet, the number is counted as 1. The packet to be counted includes the packet having the largest sequence number received by the packet receiving unit 220 until the packet receiving unit 220 receives all the packets having the sequence numbers n + 1 to m + 1. All packets that fall between the packets of number n + 1. The estimation unit 230 sets the number d _{i in} which the sequence numbers are arranged in descending order for the packet sequence selected so as to maximize this number for each interface as candidates for the estimated number of branches of the interface IFi.

The estimation unit 230 determines that the number d _{i in} which the sequence numbers are arranged in descending order is greater than the estimated number k _{i of} branch numbers for the packet sequence selected so that the number in which the sequence numbers are arranged in descending order is the maximum counted in step S1305. For example, the number d _{i in} which the sequence numbers are arranged in descending order is set as a candidate for the estimated value k _i of the number of branches (step S1306). Then, the estimation unit 230 determines that the packet having the largest sequence number received by the packet receiving unit 120 and the sequence number of all packets having the sequence numbers n + 1 to m are received by the packet receiving unit 120. It is determined whether all the packets that fall between the n + 1th packet have been received (step S1307). If all the packets have been received, the estimating unit 230 stores the estimated number k _{i of the} number of branches determined as a candidate in step S1306 in the information unit 280 (step S1308). On the other hand, if all the packets have not been received yet, the process returns to step S1304, and the estimation unit 230 further executes a process of acquiring the sequence number of the next received packet.

  Thus, the estimation unit 230 can estimate the number of branches for each interface in the network 10. The receiving terminal 200B can determine whether or not a packet is missing using the number of branches estimated by the estimation unit 230.

  The operation of the estimation unit 230 has been described in detail with reference to FIG. Next, the operation of the missing determination unit 240 included in the receiving terminal 200B according to the second embodiment of the present invention will be described.

  FIG. 14 is a flowchart showing the operation of the missing determination unit 240 included in the receiving terminal 200B according to the second embodiment of the present invention. Hereinafter, the operation of the missing determination unit 240 will be described in detail with reference to FIG.

First, the drop determination unit 240 acquires, from the information unit 280, the estimated number k _{i of the} number of branches for each interface and the sequence number n of the last packet received by the data reception unit 260 in the packet drop determination process. (Step S1401). Next, the loss determination unit 240 receives the sequence number m of the packet newly received by the packet reception unit 220 and the IF number i of the packet (step S1402), and determines whether n + 1 <m is satisfied (step S1403). ).

If n + 1 ≧ m is determined as a result of the determination in step S1403, the loss determination unit 240 determines that no loss has occurred in the received packet, and ends the process. On the other hand, if n + 1 <m as a result of the determination in step S1403, the missing determination unit 140 determines whether k _i = 1 (step S1404).

As a result of the determination in step S404, if the value of the number of branches k _i held by the information unit 180 is k _i = 1, it is determined that the received packet is missing, and the missing decision unit 240 Notifies the response unit 270 of the packet loss (step S1405). In this step S1405, the loss determination unit 240 determines that the packet with the sequence number from the (n + 1) th to the previous sequence number before the smallest sequence number among the numbers greater than the (n + 1) th received is missing. The response unit 270 is notified of packet loss.

On the other hand, as a result of the determination in step S1404, if the value of the number of branches k _i held in the information unit 280 is not k _i = 1, then the drop determination unit 240 receives the packet reception unit 220 next. The sequence number of the received packet is acquired (step S1406).

  When the packet receiving unit 220 acquires the sequence number of the next packet received in step S1406, the missing determination unit 240 determines whether the sequence number acquired in step S1406 is n + 1 (step S1407). .

As a result of the determination in step S1407, if the order number acquired in step S1406 is n + 1, the lack determination unit 240 ends the process. On the other hand, as a result of the determination in step S1407, if the sequence number acquired in step S1406 is not n + 1, the loss determination unit 240 subsequently includes the packet of sequence number m, and n + 1 received by the packet reception unit 220 thereafter. Packets having a larger order number are arranged in the order received by the packet receiving unit 220. Then, packets are selected for each interface from the packet sequence in the same order. Then, for the packet sequence selected for each interface, the number d _{i in} which the sequence numbers are arranged in descending order for each interface is counted up (step S1408).

Then, the missing determination unit 240 determines whether or not there is a column satisfying k _i ≦ d _i for the number d _i counted in step S1408 (step S1409). If there is at least one column satisfying k _i ≦ d _i for all interfaces, it is determined that the received packet is missing, and the missing decision unit 240 notifies the response unit 270 of the missing packet (step) S1405). On the other hand, if a _d i _{<k i} also _{d i} of which column, returns to step S1406, the missing determination unit 240 acquires the sequence number of the packet next received packet reception unit 220.

  The operation of the missing determination unit 240 has been described in detail with reference to FIG. Next, the operation of the buffer 250 included in the receiving terminal 200B according to the second embodiment of the present invention will be described.

  FIG. 15 is a flowchart for explaining the operation of the buffer 250 included in the receiving terminal 200B according to the second embodiment of the present invention. Hereinafter, the operation of the buffer 250 will be described with reference to FIG.

  First, when the buffer 250 receives a packet from the packet receiving unit 220 (step S1501), the buffer 250 passes the received packet to the data receiving unit 260 in ascending order of the sequence number given to the received packet (step S1502). If there is a packet with the missing sequence number, the buffer 250 waits until the packet is sent from the packet receiving unit 220. In addition, if there is a packet that has already been duplicated to the data receiving unit 260, the buffer 250 discards the packet.

  Then, the buffer 250 passes the sequence number of the last packet passed to the data receiving unit 260 to the information unit 280.

  The operation of the buffer 250 has been described above with reference to FIG. Next, the operation of the response unit 270 included in the receiving terminal 200B according to the second embodiment of the present invention will be described.

  FIG. 16 is a flowchart showing the operation of the response unit 270 according to the second embodiment of the present invention. Hereinafter, the operation of the response unit 270 according to the second embodiment will be described with reference to FIG.

  The response unit 270 acquires the sequence number n of the last packet received by the data receiving unit 260 from the information unit 280 (step S1601). Next, the response unit 270 confirms whether or not a packet exists in the buffer 250 (step S1602).

  As a result of the confirmation in the step S1602, if there is no packet in the buffer 250 or if there is a packet whose sequence number is n + 1, the packet can be received according to the sequence number. A response packet is transmitted with at least one of the contents of (1) or (2), and the process is terminated.

  On the other hand, as a result of the confirmation in step S1602, if there is a packet with the sequence number n + 2 or later in the buffer 250, has the response unit 270 received the notification of the deletion of the packet with the sequence number n + 1 from the loss determination unit 240? Whether or not is confirmed (step S1603). If there is no notification of the loss of the packet with the sequence number n + 1 from the loss determination unit 240, the process returns to step S1602, and the response unit 270 refrains from transmitting the response packet. On the other hand, if the notification of the loss of the packet with the sequence number n + 1 is received from the loss determination unit 240, the response unit 270 informs the transmitting terminal 200A that the packet with the sequence number n + 1 is missing by using the response packet. Notification is made (step S1604). This notification is performed according to at least one of the above-described (1) and (2).

  The operation of the response unit 270 according to the second embodiment has been described above with reference to FIG. As described above, the response unit 270 refrains from transmitting a response packet until it receives a notification of the loss of the packet with the sequence number n + 1 from the loss determination unit 240, thereby suppressing generation of useless traffic to the network 10.

  Here, specific operation examples of the estimation unit 230, the loss determination unit 240, the buffer 250, and the response unit 270 will be described. The transmitting terminal 200A transmits, to the receiving terminal 200B, the data packets to which the sequential numbers subsequent to 1, 2, 3,. Hereinafter, when there is a description about the packet number, this sequence number is indicated unless otherwise specified. In addition, it is assumed that the data packet is assigned either IF number 1 or 2 of the interface through which the transmitting terminal 200A transmits the data packet. The receiving terminal 200B receives the data packet transmitted by the transmitting terminal 200A, and transmits one response packet to the transmitting terminal 100A every time one packet is received.

  There is a possibility that both the data packet transmitted from the transmitting terminal 200A and the response packet transmitted from the receiving terminal 200B are distributed to a plurality of paths by a router (not shown) or the like in the network 10 along the path. However, neither the transmission terminal 200A nor the reception terminal 200B knows how many routes are distributed.

Here, it is assumed that the receiving terminal 200B has received the data packets in order up to No. 10, and has received all the packets received by the data receiving unit 260. Hereinafter, the operation of the receiving terminal 200B regarding the packet received from the transmitting terminal 200A will be specifically described with reference to the drawings. At this time, the information unit 280 stores the last sequence number 10 received by the data receiving unit 260 and the estimated values k ₁ = 1 and k ₂ = 1 of the number of branching paths.

  At this time, it is assumed that the packet receiving unit 220 receives the 13th packet. The 13th packet received by the packet receiving unit 220 is transferred to the buffer 250. Then, when the packet receiving unit 220 receives the packets in the order shown in FIG. 17 including the 13th packet, the operation of the estimating unit 230 will be described with reference to the flowchart shown in FIG.

First, the estimation unit 230 acquires the estimated number k ₁ = 1 and k ₂ = 1 of the number of branches from the information unit 280 and the sequence number n = 10 of the last packet received by the data reception unit 260. (Step S1301). Subsequently, the estimating unit 230 acquires the sequence number m = 13 of the packet newly received by the packet receiving unit 220 and the IF number i = 2 of the packet (step S1302). The estimation unit 230 determines whether m−n ≦ k ₂ is satisfied (step S1303). Since k ₂ <mn, the estimation unit 230 determines that the packet reception unit 220 has the packet with the sequence number m = 13. Next, the sequence number (12) of the received packet and the IF number i = 1 of the packet are acquired (step S1304).

Subsequently, the estimation unit 230 counts up the numbers d ₁ and d _{2 in} which the order numbers are arranged in descending order for each interface (step S1305). Here, the values of d ₁ and d ₂ are d ₁ = d ₂ = 1. Since a d _i ≦ k _i for any interface, the estimation unit 230 includes a sequence number largest packet that the packet receiving unit 220 receives (# 13 packet), the sequence number is n + 1 th packet (number 11 ) Is received (step S1307). Since the 11th packet has not been received, all the packets have not been received, so the process returns to step S1304 to estimate. The unit 230 further executes processing for acquiring the sequence number of the next received packet.

Thereafter, when the packet receiving unit 220 receives up to the 14th packet, the estimating unit 230 obtains the sequence number (14) of the packet received by the packet receiving unit 220 and the IF number i = 2 of the packet (step S1304). ). The estimation unit 230 counts up the numbers d ₁ and d _{2 in} which the order numbers are arranged in descending order for each interface (step S1305). Here, number 16 for the interface 1, 15th, next _d 1 = 3 in sequence of 14 th, 12 th for interface 2, and _d 2 = 2 a sequence of 11th. Then, the estimating unit 230 sets the number of descending order numbers as candidates for the estimated number k _i of the number of branches for each interface (step S1306).

Subsequently, the estimation unit 230 receives all packets received between the packet having the largest sequence number (the 13th packet) received by the packet receiving unit 220 and the packet having the sequence number of n + 1 (the 11th). Since all packets have been received, the estimation unit 230 sets the estimated number k ₁ = 3 and k ₂ = 2 of the number of branches for each interface, which are candidates in step S1306. The information is stored in the information unit 180 (step S1308).

Next, an operation after the estimation unit 230 estimates the estimated number of branches for each interface as k ₁ = 3 and k ₂ = 2 will be described. Here, a case where the receiving terminal 200B receives a packet from the transmitting terminal 200A as shown in FIG. 18 will be described. The information unit 280 stores the sequence number (20) of the last packet received by the data receiving unit 260 and the estimated number of branches for each interface, k ₁ = 3 and k ₂ = 2.

In the packet loss determination process, the loss determination unit 240 determines that the estimated number of branches for each interface is k ₁ = 3 and k ₂ = 2 from the information unit 280 and the order of the last packet received by the data reception unit 260. Number n = 20 is acquired (step S1401). Next, the loss determination unit 240 receives the sequence number m = 27 of the packet newly received by the packet receiving unit 220 and the IF number i = 1 of the interface that transmitted the packet (step S1402). Since the sequence number m (= 27) of the received packet is not n + 1 (= 21), the drop determining unit 240 next receives the sequence number m = 26 of the packet received by the packet receiving unit 220 and the interface that transmitted the packet. IF number i = 2 is received. Since the sequence number m (= 26) of the received packet is not n + 1 (= 21), the missing determination unit 240 checks whether there is a packet sequence that satisfies k _i ≦ d _i for all interfaces. .

As a result of the confirmation, there is no packet sequence that satisfies k _i ≦ d _i , and thereafter, the loss determination unit 240 subsequently determines the sequence number of the packet received by the packet reception unit 220 and the IF number of the interface that transmitted the packet. Repeat the acquisition process. When the 25th packet is received, there is a packet sequence that satisfies k _i ≦ d _i for all interfaces (for the interface 1, the packet sequence consisting of 26th, 24th, 23rd, (The packet sequence consisting of No. 27 and No. 25 for the interface 2), and then the missing determination unit 240 starts from the n + 1 = 21st packet, and the smallest sequence number among the numbers larger than n + 1 = 21 received so far It is determined that the packet up to the 22nd, that is, the 22nd packet is missing, and the response unit 270 is notified accordingly.

  The buffer 250 receives the packet from the packet receiving unit 220, but since the 21st packet is missing, the buffer 250 waits until the 21st packet is sent from the packet receiving unit 220. Note that the buffer 250 holds the packet received from the packet receiving unit 220.

  In addition, the response unit 270 acquires the sequence number n = 20 of the last packet received by the data receiving unit 260 from the information unit 280 (step S1601). The response unit 270 confirms whether or not the 21st packet exists in the buffer 250 (step S1602). Since only the n + 1 (23) th and subsequent packets exist in the buffer 250, the response unit 270 is missing. It is confirmed whether or not the notification of the loss of the packets of the sequence numbers 21 and 22 is received from the determination unit 240 (step S1603). Since there is a notification that the 21st and 22nd packets are missing from the missing determination unit 240, a response is sent to the sending terminal 200A that the 21st and 22nd packets are missing. Notify by packet. The response unit 270 transmits a response packet to the transmission terminal 200A with at least one of the contents (1) and (2) determined in advance, and ends the process.

  The specific operation examples of the estimation unit 230, the loss determination unit 240, the buffer 250, and the response unit 270 have been described above.

  As described above, according to the receiving terminal 200B according to the second embodiment of the present invention, when the transmitting terminal 200A transmits a packet from a plurality of interfaces, the sequence number of the packet received by the packet receiving unit 220 is used. The estimation unit 230 estimates the number of branches of the internal path of the network 10 for each interface, and even when the packet is not received according to the number, the information on the number of branches is used to determine the response packet from the response unit 270. Refrain from sending. As a result, the receiving terminal 200B does not erroneously determine that the packet loss is in the middle of the route even when the packet arrival order is reversed due to the branch in the middle of the communication route.

  In the invention disclosed in Non-Patent Document 1, since the arrival order is not guaranteed due to branching along the route, when a packet with a larger order number arrives first at the receiving terminal, a packet with a smaller order number is automatically lost. Therefore, retransmission from the transmitting terminal occurs due to the response packet. For example, as described above, in the invention disclosed in Non-Patent Document 1, when a packet arrives as shown in FIG. 7, the 11th and 12th packets are subject to retransmission when the 13th packet arrives. .

  In the invention disclosed in Patent Document 2, since only the first packet in the buffer is seen in the reception buffer, when a packet with a large sequence number arrives first on the receiving terminal side, a packet with a smaller sequence number is automatically detected. Therefore, it is determined that the packet is lost, and a response packet is transmitted and a packet is retransmitted from the transmitting terminal. When the packet arrives at the receiving terminal as shown in FIG. 18, according to the invention disclosed in Patent Document 2, when the packet with the sequence number of 26 is received, the packets of the 21st to 25th packets are automatically lost. It will be judged and will be subject to retransmission of the packet.

  On the other hand, the receiving terminal 200B according to the second embodiment of the present invention determines whether a packet has arrived from a packet that arrives later. Therefore, when the 26th packet arrives, the receiving terminal 200B immediately receives the 21st to 25th packets. No. packet is not subject to retransmission. Therefore, according to the second embodiment of the present invention, even when a packet does not arrive according to the number, it is not determined whether a packet has arrived at the time of arrival of the packet, but is also determined from a packet that arrives later. Therefore, it is possible to prevent unnecessary traffic from flowing through the network.

  The configuration described in each of the above embodiments is generally applied to those used by configuring a network. For example, the present invention can be applied to a P2P (Peer to Peer) virtual network structure or a wireless ad hoc network.

  Further, in each of the above embodiments, the steps described in the flowcharts are performed in parallel or individually even if they are not necessarily processed in time series, as well as processes performed in time series in the described order. Also includes processing to be performed. Further, it goes without saying that the order can be appropriately changed even in the steps processed in time series.

  The various operations in the above embodiments may be executed by hardware processing or software processing. When performing various operations in the above embodiments by software processing, the receiving terminals 100B and 200B are provided with a recording medium storing a computer program and a processor or other control means for executing the computer program. The computer program may be read out from the program and sequentially executed by the control means.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  The present invention can be applied to a communication apparatus and a communication control method, and is particularly applicable to communication that guarantees the arrival of data when a certain love data is transmitted, for example, TCP or SCTP.

100A, 200A Transmission terminal 100B, 200B Reception terminal 120, 220 Packet reception unit 130, 230 Estimation unit 140, 240 Missing determination unit 150, 250 Buffer 160, 260 Data reception unit 170, 270 Response unit 180, 280 Information unit

Claims (10)

In a receiving terminal that receives a packet in which a sequence of packets of a predetermined interval is transmitted with a sequence number assigned from a transmitting terminal via a network,
A packet receiver for receiving packets;
An estimation unit that estimates and calculates the number of branches of the network path from the reception order of the packets received by the packet reception unit;
A missing determination unit for determining a packet lost in the middle of the route from the reception order and the number of branches;
A packet holding unit for holding a packet received by the packet receiving unit;
From the packet held in the packet holding unit and the sequence number of the packet determined to be missing by the missing determination unit, a response unit that requests retransmission of the lost packet to the transmission terminal;
A communication apparatus comprising:   The estimation unit receives the packets up to the sequence number n (n is an integer equal to or greater than 0) and then receives all the packets of the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the largest sequence number received by the packet receiving unit until the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between packets of sequence number n + 1, in a column selected so that the number of sequence numbers in descending order is the maximum in the sequence in which the received packets are arranged in the order received by the packet receiver. The communication apparatus according to claim 1, wherein the number of the sequence numbers arranged in descending order is estimated as the number of branches of the route.   After the packet receiving unit has received all the packets up to the order number n (n is an integer equal to or greater than 0), the missing determination unit is the mth greater than the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the maximum sequence number received by the packet receiving unit before the packet receiving unit receives all the packets from the sequence numbers n + 1 to m And for all received packets that fall between the packets of sequence number n + 1, the number estimated by the estimation unit is the number of the sequence numbers arranged in descending order in the sequence in which the received packets are arranged in the order received by the packet reception unit. If there is a packet whose number is greater than or equal to the number of branches in the route, the smallest sequence number among the received packets that are greater than the sequence number n + 1 from the sequence number n + 1 And judging that the packet until one front is missing, the communication apparatus according to claim 1 or 2.   The response unit receives a packet up to the sequence number n (n is an integer equal to or greater than 0) after the packet reception unit receives the packet, and the packet of the sequence number n + 1 is received even if the packet reception unit receives the packet. The packet re-transmission request is withheld until the loss determination unit determines that the packet with the sequence number n + 1 is missing when the packet holding unit does not exist. Communication device. In a receiving terminal that receives a packet in which a sequence of packets of a predetermined interval is transmitted from a transmitting terminal via a network with a sequence number and an interface identifier assigned by a plurality of transmitting interfaces,
A packet receiver for receiving packets;
An estimation unit for estimating and calculating the number of branches of the network path from the reception order of the packets received by the packet reception unit and the interface identifier;
A loss determination unit for determining a packet lost in the middle of the route from the reception order, the interface identifier, and the number of branches;
A packet holding unit for holding a packet received by the packet receiving unit;
From the packet held in the packet holding unit and the sequence number of the packet determined to be missing by the missing decision unit, a response unit that requests retransmission of the missing packet;
A communication apparatus comprising:   The estimation unit receives the packets up to the sequence number n (n is an integer equal to or greater than 0) and then receives all the packets of the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the largest sequence number received by the packet receiving unit until the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between the packets of sequence number n + 1, the sequence numbers are arranged in descending order in a sequence in which the received packets from a transmission interface are extracted from the received packets and arranged in the order received by the packet receiver. Estimating the number of branches of the route in the transmission interface in the descending order of the sequence numbers in the column selected to maximize the number. Wherein, the communication apparatus according to claim 5.   After the packet receiving unit has received all the packets up to the order number n (n is an integer equal to or greater than 0), the missing determination unit is the mth greater than the sequence number n + 1 (m is an integer equal to or greater than 2). When the packet receiving unit receives the packet, the packet having the maximum sequence number received by the packet receiving unit before the packet receiving unit receives all the packets from the sequence numbers n + 1 to m For all received packets that fall between the packet and the sequence number n + 1, the sequence number is descending in a sequence in which the received packets from a transmission interface are extracted from the received packets and arranged in the order received by the packet receiver. If the number of lines equal to or greater than the number of branches of the route estimated by the estimation unit is established for all transmission interfaces, the sequence number n + 1 7. The communication according to claim 5, wherein it is determined that a packet up to one prior to the smallest sequence number among the received packets larger than the sequence number n + 1 is determined to be missing. apparatus.   The response unit receives a packet up to the sequence number n (n is an integer equal to or greater than 0) after the packet reception unit receives the packet, and the packet of the sequence number n + 1 is received even if the packet reception unit receives the packet. The packet retransmission request according to any one of claims 5 to 7, wherein if the packet holding unit does not exist, the packet retransmission request is refrained until the missing determination unit determines that the packet with the sequence number n + 1 is missing. Communication device. A packet receiving step of receiving a packet in which a sequence of packets of a predetermined interval is transmitted with a sequence number assigned from a transmitting terminal via a network;
An estimation step for estimating and calculating the number of branches of the network path from the reception order of the packets received in the packet reception step;
Deletion determination step for determining a packet lost in the middle of the route from the reception order and the number of branches;
A packet holding step for holding the packet received in the packet receiving step;
From the packet held in the packet holding step and the sequence number of the packet determined to be missing in the missing determination step, a response step for requesting the transmitting terminal to retransmit the missing packet;
A communication control method comprising: A packet receiving step of receiving a packet in which a sequence of packets of a predetermined interval is transmitted from a transmitting terminal via a network with a sequence number and an interface identifier assigned by a plurality of transmitting interfaces;
An estimation step of estimating and calculating the number of branches of the network path from the reception order of the packets received in the packet reception step and the interface identifier;
Deletion determination step of determining a packet lost during the route from the reception order, the interface identifier, and the number of branches;
A packet holding step for holding the packet received in the packet receiving step;
A response step for requesting retransmission of the missing packet from the packet held in the packet holding step and the sequence number of the packet determined to be missing in the missing decision step;
A communication control method comprising:

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