Communication device, method for estimating round-trip time, and program for estimating round-trip time

Abstract

To appropriately estimate an RTT.SOLUTION: A communication device 2 transmits a communication packet to an opposite device and receives an acknowledgement packet for the communication packet from the opposite device. The communication device includes a sequence information acquisition unit 9 that acquires sequence information of the communication packet and the acknowledgement packet, and an RTT estimation unit 10 that estimates an RTT based on three times: a transmission time of at least one communication packet, a reception time of one acknowledgement packet, and either a transmission time of another communication packet or a reception time of another acknowledgement packet based on an acquisition result of the sequence information acquisition unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication device, a method for estimating a round trip time, and a program for estimating a round trip time. [Background technology]

[0002] In packet communication, a communication device transmits a communication packet to an opposite device, and when the opposite device receives the communication packet from the communication device, it transmits a delivery confirmation packet for the communication packet to the communication device. For example, Patent Document 1 discloses a technique for estimating a round trip time (hereinafter sometimes referred to as RTT) based on the transmission time of the communication packet and the reception time of the delivery confirmation packet when sequence information of the communication packet transmitted from the communication device to the opposite device and sequence information of the delivery confirmation packet transmitted from the opposite device to the communication device match. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Pat. No. 1,516,098 Summary of the Invention [Problem to be solved by the invention]

[0004] In the method disclosed in Patent Document 1, in order to identify a delivery confirmation packet that matches the sequence information of a communication packet, it is necessary to determine the sequence information of a plurality of delivery confirmation packets including those before and after the delivery confirmation packet whose sequence information matches. Therefore, there is a problem that the processing load increases. In addition, even if a delivery confirmation packet that matches the sequence information of a communication packet is identified, if the delivery confirmation packet is a delayed packet or a duplicate packet, there is also a problem that the estimation accuracy of the RTT decreases.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a communication device, a method for estimating round trip time, and a program for estimating round trip time that can appropriately estimate round trip time. [Means for solving the problem]

[0006] According to the invention recited in claim 1, a communication packet is transmitted to an opposing device, and a delivery confirmation packet for the communication packet is received from the opposing device. A sequence information acquisition unit (9) acquires sequence information of the communication packet and the delivery confirmation packet. A round trip time estimation unit (10) estimates a round trip time based on the acquisition result of the sequence information acquisition unit, based on three times: a transmission time of at least one of the communication packets, a reception time of one of the delivery confirmation packets, and either a transmission time of another of the communication packets or a reception time of another of the delivery confirmation packets.

[0007] The round trip time is estimated based on three times: the transmission time of at least one communication packet, the reception time of one delivery confirmation packet, and either the transmission time of another communication packet or the reception time of another delivery confirmation packet. There is no need to determine sequence information of a plurality of delivery confirmation packets including those before and after the delivery confirmation packet with matching sequence information, and an increase in processing load can be avoided. There is no need to identify a delivery confirmation packet that matches the sequence information of the communication packet, and a decrease in the estimation accuracy of the RTT can also be avoided. It is possible to avoid both an increase in processing load and a decrease in estimation accuracy, and the round trip time can be appropriately estimated. [Brief description of the drawings]

[0008] [Figure 1] A functional block diagram showing the overall configuration of one embodiment. [Diagram 2] 1 is a flowchart showing an RTT estimation process according to a first method. [Diagram 3]A diagram explaining the RTT estimation process using the first method. [Figure 4] A diagram explaining the RTT estimation process using the first method. [Diagram 5] Flowchart showing the RTT estimation process according to the second method [Figure 6] A diagram explaining the RTT estimation process using the second method. [Figure 7] A diagram explaining the RTT estimation process using the second method. [Figure 8] Flowchart showing the process of estimating the lower limit of the RTT fluctuation range [Figure 9] A diagram explaining the process of estimating the lower limit of the RTT fluctuation range [Figure 10] A diagram explaining the process of estimating the lower limit of the RTT fluctuation range DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment in which the present invention is applied to a communication node mounted on a vehicle, for example, will be described with reference to the drawings. As shown in FIG. 1, a communication system 1 is configured such that a communication node 2 (corresponding to a communication device) and a corresponding node 3 (corresponding to a corresponding device) can communicate data via a wireless line. The data communication between the communication node 2 and the corresponding node 3 is data communication conforming to the communication protocol TCP / IP (Transmission Control Protocol / Internet Protocol). The communication node 2 transmits a communication packet to the corresponding node 3 via a wireless line. When the corresponding node 3 receives a communication packet from the communication node 2, it transmits a delivery confirmation packet for the received communication packet to the communication node 2 via a wireless line. Note that the communication node 2 and the corresponding node 3 may be configured to be able to communicate data via a base station, and the communication node 2 and the base station may communicate data via a wireless line, and the corresponding node 3 and the base station may communicate data via a wired line.

[0010] The communication node 2 transmits driving control data relating to driving control such as vehicle speed, acceleration / deceleration, sharp turns, driving route, fuel consumption, etc. to the opposing node 3. The opposing node 3 is capable of data communication with multiple communication nodes 2 via wireless lines, and is, for example, a server having a function of statistically processing driving control data for an unspecified number of vehicles. When the opposing node 3 receives driving control data from each communication node 2 mounted on an unspecified number of vehicles, it statistically processes the received driving control data. Note that the data transmitted and received between the communication node 2 and the opposing node 3 may be data other than the above-mentioned driving control data, or may be data used for other purposes.

[0011] The communication node 2 includes a control unit 4 that controls the operation of the entire node. The control unit 4 is mainly configured with a microcomputer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and I / O (Input / Output), etc. The functions provided by the control unit 4 can be provided by software recorded in a physical memory device and a computer that executes the software, software only, hardware only, or a combination of these. For example, when the control unit 4 is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a large number of logic circuits or an analog circuit. When the control unit 4 executes a program stored in a non-transitive physical recording medium, a process corresponding to the program is executed, and a method corresponding to the program is executed.

[0012] The control unit 4 includes, for each function, a packet generation unit 5, a vehicle inside communication interface unit 6 (corresponding to a packet receiving unit), a vehicle outside communication interface unit 7, a processing scheduling unit 8, a sequence information acquisition unit 9, an RTT estimation unit 10, a judgment value calculation unit 11, and a fluctuation width estimation unit 12. Each of these units 5 to 12 executes an RTT estimation program and performs an RTT estimation method.

[0013] The packet generation unit 5 generates a communication packet in accordance with the execution of the application by the control unit 4, and outputs the generated communication packet to the sequence information acquisition unit 9. When the vehicle inside communication interface unit 6 receives a communication packet from an external node 13 (corresponding to an external device), it outputs the received communication packet to the sequence information acquisition unit 9.

[0014] The vehicle exterior communication interface unit 7 transmits the communication packet to the opposing node 3 via a wireless line. The processing scheduling unit 8 schedules the processing of the communication packet and the delivery confirmation packet. When the processing of the communication packet and the delivery confirmation packet is scheduled by the processing scheduling unit 8, the sequence information acquisition unit 9 acquires the sequence numbers (corresponding to sequence information) of the communication packet and the delivery confirmation packet whose processing has been scheduled. The sequence numbers are information that can specify the transmission order of the communication packets and the reception order of the delivery confirmation packets, respectively. As long as the transmission order of the communication packets and the reception order of the delivery confirmation packets can be specified, respectively, information other than the sequence numbers may be used instead of the sequence numbers.

[0015] When the sequence numbers of the communication packets and the delivery confirmation packet are acquired by the sequence information acquisition unit 9, the RTT estimation unit 10 estimates the RTT based on the transmission time of the communication packets and the reception time of the delivery confirmation packet from the acquisition result. There are a first method of estimating the RTT based on the transmission time of one communication packet and the reception time of two delivery confirmation packets, and a second method of estimating the RTT based on the transmission time of two communication packets and the reception time of one delivery confirmation packet.

[0016] In the first method, the RTT estimation unit 10 estimates the RTT on the condition that two acknowledgement packets are received after one communication packet is transmitted, when the sequence number of the latter acknowledgement packet matches the sequence number of the communication packet, or when the sequence number between the sequence numbers of the two acknowledgement packets matches the sequence number of the communication packet. In the second method, the RTT estimation unit 10 estimates the RTT on the condition that one acknowledgement packet is received after two communication packets are transmitted, when the sequence number of the former communication packet matches the sequence number of the acknowledgement packet, or when the sequence number between the sequence numbers of the two communication packets matches the sequence number of the acknowledgement packet.

[0017] The judgment value calculation unit 11 calculates the upper and lower limits of the RTT for each sample for a plurality of samples in a predetermined measurement period, and calculates the minimum value of the calculated plurality of upper limits as an upper limit judgment value and calculates the maximum value of the calculated plurality of lower limits as a lower limit judgment value. When the judgment value calculation unit 11 calculates the upper limit judgment value and the lower limit judgment value, the fluctuation range estimation unit 12 compares the calculated upper limit judgment value with the lower limit judgment value, and if the upper limit judgment value is smaller than the lower limit judgment value, estimates the difference between the upper limit judgment value and the lower limit judgment value as the lower limit of the RTT fluctuation range.

[0018] Next, the operation of the above-mentioned configuration will be described with reference to Fig. 2 to Fig. 10. Here, an RTT estimation process for estimating an RTT and an RTT fluctuation range lower limit estimation process for estimating a lower limit of the RTT fluctuation range will be described.

[0019] (1) RTT estimation process As described above, there are two methods for estimating the RTT: the first method and the second method. Each method will be explained below.

[0020] (1-1) RTT estimation process using the first method (see Figures 2 to 4) The control unit 4 starts the RTT estimation process by the first method, and when a request to transmit a communication packet occurs, it acquires the sequence number of the communication packet that is the target of the transmission request (S1, which corresponds to the first information acquisition step). When the control unit 4 transmits the communication packet to the remote node 3, it stores the transmission time of the communication packet in association with the acquired sequence number of the communication packet (S2).

[0021] When the control unit 4 receives a delivery confirmation packet from the remote node 3, it acquires the sequence number of the received delivery confirmation packet (S3, which corresponds to the second information acquisition step). The control unit 4 stores the reception time of the delivery confirmation packet in association with the sequence number of the acquired delivery confirmation packet (S4).

[0022] When the control unit 4 receives another delivery acknowledgment packet from the remote node 3, it acquires the sequence number of the received another delivery acknowledgment packet (S5, which corresponds to the second information acquisition step). The control unit 4 stores the reception time of the another delivery acknowledgment packet in association with the sequence number of the acquired another delivery acknowledgment packet (S6).

[0023] The control unit 4 determines whether the conditions for estimating the RTT are met. The control unit 4 determines whether the sequence number of the latter acknowledgement packet matches the sequence number of the communication packet (S7). If the control unit 4 determines that they match (S7: YES), it estimates the RTT based on three times: the transmission time of one communication packet and the reception times of two acknowledgement packets (S9), and ends the RTT estimation process using the first method.

[0024] On the other hand, if the control unit 4 determines that there is no consistency (S7: NO), it determines whether the sequence number between the sequence numbers of the two delivery confirmation packets is consistent with the sequence number of the communication packet (S8). If the control unit 4 determines that there is a consistency (S8: YES), it also estimates the RTT based on the three times, the transmission time of one communication packet and the reception time of the two delivery confirmation packets (S9), and ends the RTT estimation process using the first method. On the other hand, if the control unit 4 determines that there is no consistency (S8: NO), it ends the RTT estimation process using the first method without estimating the RTT.

[0025] As shown in FIG. 3, when the control unit 4 transmits a communication packet with sequence number "s1" to the counterpart node 3 at transmission time "Ts(s1)", receives a delivery confirmation packet with sequence number "s1-an" from the counterpart node 3 at reception time "Ta(s1-an)", and receives a delivery confirmation packet with sequence number "s1+bn" from the counterpart node 3 at reception time "Ta(s1+bn)", where "n" is the segment size, a>0, b>=0, the control unit 4 estimates the RTT using the following formula. Ta(s1-an)-Ts(s1) <RTT<Ta(s1+bn)-Ts(s1) That is, the control unit 4 estimates that the RTT is within a range having Ta(s1-an)-Ts(s1) as the lower limit and Ta(s1+bn)-Ts(s1) as the upper limit.

[0026] The control unit 4 calculates the difference between the upper and lower limits of the RTT for each sample as an estimation error for multiple samples in a predetermined measurement period. As shown in Fig. 4, the control unit 4 estimates the difference between the upper and lower limits associated with the transmission of a communication packet with sequence number "s1" as an estimation error using the following calculation formula. Estimation error = Ta(s1+bn)-Ta(s1-an)

[0027] When the control unit 4 transmits a communication packet with sequence number “s2” following transmission of a communication packet with sequence number “s1”, it sets c>0, d>=0 and similarly estimates the RTT using the following formula. Ta(s2-cn)-Ts(s2) <RTT<Ta(s2+dn)-Ts(s2) That is, the control unit 4 estimates that the RTT is within a range having Ta(s2-cn)-Ts(s2) as the lower limit and Ta(s2+dn)-Ts(s2) as the upper limit. The control unit 4 estimates the difference between the upper limit and the lower limit associated with the transmission of the communication packet with sequence number "s2" as an estimation error using the following calculation formula. Estimation error = Ta(s1+dn)-Ta(s1-cn)

[0028] After calculating the estimation error for each of a plurality of samples in this manner, the control unit 4 estimates the RTT for a sample with a relatively small calculated estimation error. The control unit 4 performs statistical processing on samples with an estimation error of x% or less of the average of all samples as valid samples to estimate the RTT. "x" is, for example, a value that satisfies the estimation accuracy required by the system. In the example of FIG. 4, the estimation error of the communication packet sample with sequence number "s2" is smaller than that of the communication packet sample with sequence number "s1", so there is a high possibility that the communication packet sample with sequence number "s2" will be adopted as a valid sample.

[0029] (2) RTT estimation process using the second method (see Figures 5 to 7) The control unit 4 starts the RTT estimation process by the second method, and when a request to transmit a communication packet occurs, it acquires the sequence number of the communication packet that is the target of the transmission request (S11, which corresponds to the first information acquisition step). When the control unit 4 transmits the communication packet to the remote node 3, it stores the transmission time of the communication packet in association with the acquired sequence number of the communication packet (S12).

[0030] When a transmission request for another communication packet occurs, the control unit 4 acquires the sequence number of the other communication packet that is the target of the transmission request (S13, which corresponds to a first information acquisition step). When the control unit 4 transmits the other communication packet to the opposing node 3, it stores the transmission time of the communication packet in association with the acquired sequence number of the other communication packet (S14).

[0031] When the control unit 4 receives the delivery confirmation packet from the remote node 3, it acquires the sequence number of the received delivery confirmation packet (S15, which corresponds to the second information acquisition step). The control unit 4 stores the reception time of the delivery confirmation packet in association with the sequence number of the acquired delivery confirmation packet (S16).

[0032] The control unit 4 determines whether the conditions for estimating the RTT are met. The control unit 4 determines whether the sequence number of the earlier communication packet matches the sequence number of the delivery confirmation packet (S17). If the control unit 4 determines that they match (S7: YES), it estimates the RTT based on three times: the sending times of the two communication packets and the receiving time of one delivery confirmation packet (S19), and ends the RTT estimation process using the second method.

[0033] On the other hand, if the control unit 4 determines that there is no consistency (S17: NO), it determines whether or not the sequence number between the sequence numbers of the two communication packets is consistent with the sequence number of the delivery confirmation packet (S18). If the control unit 4 determines that there is a consistency (S18: YES), it also estimates the RTT based on the three times, the transmission times of the two communication packets and the reception time of one delivery confirmation packet (S19), and ends the RTT estimation process using the second method. On the other hand, if the control unit 4 determines that there is no consistency (S18: NO), it ends the RTT estimation process using the second method without estimating the RTT.

[0034] As shown in FIG. 6, when the control unit 4 transmits a communication packet with sequence number "s1-an" to the counterpart node 3 at transmission time "Ts(s1-an)", transmits a communication packet with sequence number "s1+bn" to the counterpart node 3 at transmission time "Ts(s1+bn)", and receives a delivery confirmation packet with sequence number "s1" from the counterpart node 3 at reception time "Ta(s1)", where "n" is the segment size, a>=0, b>0, the control unit 4 estimates the RTT using the following formula. Ta(s1)-Ts(s1+bn) <RTT<Ta(s1)-Ts(s1-an) That is, the control unit 4 estimates that the RTT is within a range having Ta(s1)-Ts(s1+bn) as the lower limit and Ta(s1)-Ts(s1-an) as the upper limit.

[0035] In this case, the control unit 4 also calculates the difference between the upper and lower limits of the RTT for each sample for multiple samples in a predetermined measurement period as an estimated error. As shown in Fig. 7, the control unit 4 estimates the difference between the upper and lower limits associated with the reception of the delivery confirmation packet with sequence number "s1" as an estimated error using the following calculation formula. Estimation error = Ts(s1+bn)-Ts(s1-an)

[0036] When the control unit 4 sends confirmation packets with sequence numbers "s1-an" and "s1+bn" and then confirmation packets with sequence numbers "s1-cn" and "s1+dn", it estimates the RTT using the following formula, assuming that c>=0 and d>0. Ta(s2)-Ts(s2+dn) <RTT<Ta(s2)-Ts(s2-cn) That is, the control unit 4 estimates that the RTT is within a range having Ta(s2)-Ts(s2+dn) as the lower limit and Ta(s2)-Ts(s2-cn) as the upper limit. The control unit 4 estimates the difference between the upper limit and the lower limit associated with the reception of the delivery confirmation packet with sequence number "s2" as an estimation error using the following calculation formula. Estimation error = Ts(s2+dn)-Ts(s2-cn)

[0037] After calculating the estimation error for each of a plurality of samples in this manner, the control unit 4 estimates the RTT for a sample with a relatively small calculated estimation error. The control unit 4 performs statistical processing on samples with an estimation error of x% or less of the average of all samples as valid samples, and estimates the RTT. In the example of Fig. 7, the estimation error of the delivery confirmation packet sample with sequence number "s2" is smaller than that of the delivery confirmation packet sample with sequence number "s1", so there is a high possibility that the delivery confirmation packet sample with sequence number "s2" will be adopted as a valid sample.

[0038] (2) Estimation of the lower limit of RTT fluctuation range (see Figures 8 to 10) When the control unit 4 starts the process of estimating the lower limit of the RTT fluctuation range, it calculates the upper and lower limits of the RTT for each sample for a plurality of samples in a predetermined measurement period. The control unit 4 calculates the minimum value of the calculated plurality of upper limits as the upper limit judgment value (S21), and calculates the maximum value of the calculated plurality of lower limits as the lower limit judgment value (S22).

[0039] The control unit 4 compares the upper limit judgment value with the lower limit judgment value and judges whether the upper limit judgment value is smaller than the lower limit judgment value (S23). If the control unit 4 judges that the upper limit judgment value is smaller than the lower limit judgment value (S23: YES), it estimates the difference between the upper limit judgment value and the lower limit judgment value as the lower limit of the RTT fluctuation range (S24) and ends the process of estimating the lower limit of the RTT fluctuation range. On the other hand, if the control unit 4 judges that the upper limit judgment value is not smaller than the lower limit judgment value (S23: NO), it ends the process of estimating the lower limit of the RTT fluctuation range without estimating the lower limit of the RTT fluctuation range.

[0040] As shown in Fig. 9, if the control unit 4 determines that the upper limit judgment value is smaller than the lower limit judgment value when the number of samples a to d in a predetermined measurement period is four, the control unit 4 estimates the difference between the upper limit judgment value and the lower limit judgment value as the lower limit of the RTT fluctuation range. On the other hand, as shown in Fig. 10, if the control unit 4 determines that the upper limit judgment value is not smaller than the lower limit judgment value when the number of samples e to h in a predetermined measurement period is four, the control unit 4 does not estimate the lower limit of the RTT fluctuation range.

[0041] As described above, according to this embodiment, the following advantageous effects can be obtained. In the communication node 2, the RTT is estimated based on three times: the transmission time of at least one communication packet, the reception time of one delivery confirmation packet, and either the transmission time of another communication packet or the reception time of another delivery confirmation packet. There is no need to determine the sequence numbers of multiple delivery confirmation packets including those before and after the delivery confirmation packet with a matching sequence number, so an increase in processing load can be avoided. There is no need to identify a delivery confirmation packet that matches the sequence number of a communication packet, so a decrease in the accuracy of the RTT estimation can be avoided. It is possible to avoid both an increase in processing load and a decrease in estimation accuracy, and the RTT can be appropriately estimated.

[0042] On the condition that two acknowledgement packets are received after the transmission of one communication packet, if the sequence number of the latter acknowledgement packet matches the sequence number of the communication packet, or if the sequence number between the sequence numbers of the two acknowledgement packets matches the sequence number of the communication packet, the RTT is estimated based on the transmission time of the one communication packet and the reception time of the two acknowledgement packets.The RTT can be appropriately estimated using the transmission time of the one communication packet and the reception time of the two acknowledgement packets.

[0043] On the condition that one acknowledgement packet is received after the transmission of two communication packets, if the sequence number of the earlier communication packet matches the sequence number of the acknowledgement packet, or if the sequence number between the sequence numbers of the two communication packets matches the sequence number of the acknowledgement packet, the RTT is estimated based on the transmission times of the two communication packets and the reception time of the acknowledgement packet.The RTT can be appropriately estimated using the transmission times of the two communication packets and the reception time of the acknowledgement packet.

[0044] The RTT is estimated by obtaining the sequence number of the communication packet generated by the communication node 2. The RTT can be appropriately estimated by using the sequence number of the communication packet generated by the communication node 2.

[0045] The RTT is estimated by acquiring the sequence number of the communication packet received from the external node 13. Using the sequence number of the communication packet received from the external node 13, the RTT can be appropriately estimated.

[0046] The sequence numbers of the scheduled communication packets and the delivery confirmation packets are obtained and the RTT is estimated. The RTT can be appropriately estimated using the sequence numbers of the scheduled communication packets and the delivery confirmation packets.

[0047] For multiple samples taken during a given measurement period, the difference between the upper and lower limits of the RTT for each sample is calculated as the estimation error, and the RTT is estimated for samples with a relatively small estimated error. By estimating the RTT for samples with a relatively small estimation error, the impact of delayed delivery confirmation packets can be reduced, and false detection of congestion can be avoided.

[0048] The upper and lower limits of the RTT for each sample are calculated for multiple samples during a specified measurement period, the minimum value of the multiple calculated upper limits is calculated as the upper limit judgment value, and the maximum value of the multiple lower limits is calculated as the lower limit judgment value, and when the upper limit judgment value is smaller than the lower limit judgment value, the difference between the upper limit judgment value and the lower limit judgment value is estimated as the lower limit of the RTT fluctuation range. By estimating the difference between the two when the upper limit judgment value is smaller than the lower limit judgment value as the lower limit of the RTT fluctuation range, it is possible to estimate the lower limit of the RTT fluctuation range caused by the delay of the line itself during a period when the line status is assumed to be constant, and the accuracy of the RTT estimation can be improved.

[0049] In addition to the claims, the present disclosure also includes the following inventions. [1] A communication device (2) that transmits a communication packet to an opposite device and receives a delivery confirmation packet for the communication packet from the opposite device, a sequence information acquisition unit (9) for acquiring sequence information of the communication packet and the delivery confirmation packet; and a round trip time estimation unit (10) that estimates a round trip time based on three times, namely, a sending time of at least one of the communication packets, a receiving time of one of the delivery confirmation packets, and either a sending time of another of the communication packets or a receiving time of another of the delivery confirmation packets, using the results acquired by the sequence information acquisition unit.

[0050] [2] The round trip time estimation unit estimates the round trip time based on a transmission time of one communication packet and a reception time of two delivery confirmation packets when sequence information of a later delivery confirmation packet is consistent with sequence information of the communication packet, or when sequence information between sequence information of two of the delivery confirmation packets is consistent with sequence information of the communication packet, on the condition that two delivery confirmation packets are received after transmission of one communication packet.

[0051] [3] The round trip time estimation unit estimates the round trip time based on the transmission times of two communication packets and the reception time of one delivery confirmation packet when sequence information of an earlier communication packet is consistent with sequence information of the delivery confirmation packet, or when sequence information between sequence information of two communication packets is consistent with sequence information of the delivery confirmation packet, on the condition that one delivery confirmation packet is received after transmission of two communication packets.

[0052] [4] A packet generating unit (5) for generating packets, The communication device according to any one of claims [1] to [3], wherein the sequence information acquisition unit acquires sequence information of the communication packet generated by the packet generation unit.

[0053] [5] A packet receiving unit (6) for receiving the communication packet from an external device, The communication device according to any one of claims [1] to [4], wherein the sequence information acquisition unit acquires sequence information of the communication packet received by the packet receiving unit from the external device.

[0054] [6] A scheduling unit (8) that schedules the processing of the communication packets and the delivery confirmation packets, The communication device according to any one of claims [1] to [5], wherein the sequence information acquisition unit acquires sequence information of the communication packet and the delivery confirmation packet whose processing has been scheduled by the processing scheduling unit.

[0055] [7] The communication device according to any one of claims [1] to [6], wherein the round trip time estimation unit calculates the difference between an upper limit and a lower limit of the round trip time for each sample as an estimation error for a plurality of samples in a predetermined measurement period, and estimates the round trip time for a sample for which the calculated estimation error is relatively small.

[0056] [8] a judgment value calculation unit (11) that calculates upper and lower limits of the round trip time for each of a plurality of samples during a predetermined measurement period, and calculates the minimum value of the calculated plurality of upper limits as an upper limit judgment value and calculates the maximum value of the calculated plurality of lower limits as a lower limit judgment value; and a fluctuation range estimation unit (12) that, when the upper limit judgment value calculated by the judgment value calculation unit is smaller than the lower limit judgment value, estimates a difference between the upper limit judgment value and the lower limit judgment value as a lower limit of a fluctuation range of a round trip time.

[0057] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

[0058] The control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Also, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0059] In the drawing, 1 is a communication system, 2 is a communication node (communication device), 3 is a counterpart node (counterpart device), 4 is a control unit, 5 is a packet generation unit, 6 is an in-vehicle communication interface unit (packet receiving unit), 7 is an out-vehicle communication interface unit, 8 is a processing scheduling unit, 9 is a sequence information acquisition unit, 10 is an RTT estimation unit, 11 is a judgment value calculation unit, 12 is a fluctuation range estimation unit, and 13 is an external device (external node).

Claims

1. A communication device (2) that transmits a communication packet to an opposite device and receives a delivery confirmation packet for the communication packet from the opposite device, A sequence information acquisition unit (9) that acquires sequence information of the communication packet and the delivery confirmation packet; and a round trip time estimation unit (10) that estimates a round trip time based on three times, namely, a transmission time of at least one of the communication packets, a reception time of one of the delivery confirmation packets, and either a transmission time of another of the communication packets or a reception time of another of the delivery confirmation packets, using the results acquired by the sequence information acquisition unit.

2. 2. The communication device according to claim 1, wherein the round trip time estimation unit estimates the round trip time based on a transmission time of one communication packet and a reception time of two delivery confirmation packets when sequence information of a later one of the delivery confirmation packets matches the sequence information of the communication packet, or when sequence information between the sequence information of two of the delivery confirmation packets matches the sequence information of the communication packet, on the condition that two delivery confirmation packets are received after the transmission of one communication packet.

3. 2. The communication device according to claim 1, wherein the round trip time estimation unit estimates the round trip time based on the transmission times of two communication packets and the reception time of one delivery confirmation packet when sequence information of an earlier communication packet matches sequence information of the delivery confirmation packet, or when sequence information between sequence information of two communication packets matches sequence information of the delivery confirmation packet, on the condition that one delivery confirmation packet is received after transmission of two communication packets.

4. A packet generating unit (5) for generating packets, The communication device according to claim 1 , wherein the sequence information acquisition unit acquires sequence information of the communication packet generated by the packet generation unit.

5. A packet receiving unit (6) for receiving the communication packet from an external device, The communication device according to claim 1 , wherein the sequence information acquisition unit acquires, from the external device, sequence information of the communication packet received by the packet receiving unit.

6. A scheduling unit (8) that schedules processing of the communication packet and the delivery confirmation packet, The communication device according to claim 1 , wherein the sequence information acquisition unit acquires sequence information of the communication packet and the delivery confirmation packet, the processing of which has been scheduled by the processing scheduling unit.

7. 7. The communication device according to claim 1, wherein the round trip time estimation unit calculates an estimation error, which is a difference between an upper limit and a lower limit of the round trip time for each sample, for a plurality of samples in a predetermined measurement period, and estimates the round trip time for a sample for which the calculated estimation error is relatively small.

8. a judgment value calculation unit (11) that calculates upper and lower limits of the round trip time for each of a plurality of samples during a predetermined measurement period, and calculates the minimum value of the calculated plurality of upper limits as an upper limit judgment value and calculates the maximum value of the calculated plurality of lower limits as a lower limit judgment value; and a fluctuation range estimation unit (12) that, when the upper limit judgment value calculated by the judgment value calculation unit is smaller than the lower limit judgment value, estimates a difference between the upper limit judgment value and the lower limit judgment value as a lower limit of a fluctuation range of a round trip time.

9. A communication device (2) that transmits a communication packet to an opposite device and receives a delivery confirmation packet for the communication packet from the opposite device, a first information acquisition step of acquiring sequence information of the communication packet; a second information acquisition step of acquiring sequence information of the delivery confirmation packet; A method for estimating round trip time, comprising: an estimation procedure for estimating a round trip time based on three times: a sending time of at least one of the communication packets, a receiving time of one of the delivery confirmation packets, and either a sending time of another of the communication packets or a receiving time of another of the delivery confirmation packets, using the results of the first information acquisition procedure and the results of the second information acquisition procedure.

10. A control unit (4) of a communication device (2) that transmits a communication packet to an opposite device and receives a delivery confirmation packet for the communication packet from the opposite device, a first information acquisition step of acquiring sequence information of the communication packet; a second information acquisition step of acquiring sequence information of the delivery confirmation packet; a round trip time estimation program that executes an estimation procedure that estimates a round trip time based on three times: the sending time of at least one of the communication packets, the receiving time of one of the delivery confirmation packets, and either the sending time of another of the communication packets or the receiving time of another of the delivery confirmation packets, using the results of the first information acquisition procedure and the results of the second information acquisition procedure.

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