JP2010093628A - Communication apparatus and signal transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following: it is not preferable that, even if a radio status is recovered before time-out of a TCP timer, because retransmission intervals in data missing in RLC are fixed, the TCP timer has to be time-out and a transmission rate may be reduced as a result. <P>SOLUTION: A communication apparatus includes a control unit, a first timer and a second timer. The control unit transmits data based on a first protocol to opposite-side apparatus as a transmission signal based on a lower-order second protocol than the first protocol and retransmits the transmission signal when no acknowledgement to the transmission signal is received from the opposite-side apparatus. The first timer measures the time before reducing a transmission rate of data based on the first protocol, and the second timer measures the time before retransmitting the transmission signal based on the second protocol. In accordance with the lapse of time of the first timer, the control unit changes a setting time of the second timer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication device and a signal transmission method.

  Various protocols are used for data communication in a mobile communication system.

  FIG. 1 is a diagram illustrating an example of a protocol stack used in a mobile communication system. FIG. 1 shows a protocol stack used when a user terminal (UE) 10 transmits / receives user data 12 to / from a packet data network (ie, core network) 30 via a radio network controller (RNC) 20. Yes. Specifically, on the access side, the user terminal 10 uses a protocol group indicated by reference numeral 15A, and the radio network controller 20 uses a protocol group indicated by reference numeral 25A. On the core network side, the radio network controller 20 uses a protocol group indicated by reference numeral 25C. The protocol used by the packet data network 30 is omitted.

  The user data 12 is generally TCP / IP based packet data.

  As described above, when transmitting / receiving TCP / IP-based packet data, congestion control is performed by a TCP slow start algorithm.

  FIG. 2 is a diagram for explaining a slow start algorithm in TCP. TCP is a protocol for controlling data transmission between the user terminal (UE) 10 and the packet data network (that is, the core network) 30, and the radio network control device 20 is omitted for easy understanding of the figure.

  In TCP, when the packet data network 30 transmits data to the user terminal 10 (in the downlink direction), the packet data network 30 first transmits one segment (packet) 21. When the delivery confirmation signal (ACK) 22 for this segment is received from the user terminal 10, the packet data network 30 next transmits two segments 23. When the ACK 24 for each segment is received from the user terminal 10, the packet data network 30 then transmits four segments 25. When the ACK 26 for each segment is received from the user terminal 10, the packet data network 30 transmits twice as many segments. In this way, the packet data network 30 doubles the number of segments to be transmitted at a time each time a delivery confirmation signal for each segment is received, and when the packet data network 30 reaches a certain value, increases the number of transmission segments gradually thereafter. To go.

  The same applies when the user terminal 10 transmits data to the packet data network 30 (in the uplink direction).

  On the other hand, if there is even one transmission segment (data missing) that cannot receive an acknowledgment signal (ACK) within a predetermined time (before the TCP timer times out), the packet data network 30 reduces the transmission rate and becomes congested. In order to prevent this, the number of segments transmitted at a time is reduced. Depending on how the number of segments is reduced, there are a TAHOE method that reduces the number of transmission segments to 1 when data loss occurs, and a RENO method that reduces the number of transmission segments by half when data loss occurs.

  FIG. 3A is a diagram illustrating a TAHOE method that is a method for handling data loss in TCP.

  FIG. 3B is a diagram showing a RENO method that is a method for dealing with data loss in TCP.

  Next, a radio link control (RLC) protocol that is an access-side protocol will be described. Radio link control (hereinafter referred to as RLC) provides services of transparent transmission, delivery confirmation type transmission, and non-delivery confirmation type transmission to upper layers. Here, the delivery confirmation type transmission will be described.

  FIG. 4A is a diagram illustrating a signal transmission method in RLC. RLC transmits transmission data in units of PDU (Packet Data Unit). A sequence number (SN) is assigned to the PDU. The PDU is provided with a Poll-Bit indicating whether or not a delivery confirmation signal needs to be returned.

  When the radio network control device 20 requests delivery confirmation from the user terminal 10, the radio network control device 20 sets Pol-Bit to ON and transmits the PDU 41.

  When the user terminal 10 receives the PDU 41 whose poll-bit is ON, the user terminal 10 returns a delivery confirmation signal (ACK) 42 in response thereto.

  Further, when the poll bit is not ON, the radio network control device 20 transmits a series of sequence numbers (in this case, SN = 1 to 4) of PDUs 43, and when the PDU (SN = 3) is missing, the user terminal 20 transmits a retransmission request (LIST) signal 44 to the radio network controller 20 to notify the sequence number SN = 3 of the missing PDU and make a retransmission request. When receiving this retransmission request, the radio network controller 20 retransmits the PDU (SN = 3) 45.

  Although the downlink case has been described, it goes without saying that the same applies to the uplink case.

  FIG. 4B is a diagram illustrating autonomous retransmission when data is lost in RLC. The wireless network control device 20 turns on the poll bit and transmits the PDU (SN = 0) 47. If no acknowledgment (ACK) signal is returned by a certain time T, the same PDU (SN = 0) 47 is retransmitted autonomously.

As for retransmission control in a wireless network, it has been proposed to change the retransmission timing in a transmission apparatus in order to avoid retransmitting data that is not missing. Further, in the receiving apparatus, if the order is guaranteed in the data link layer, the communication rate is lowered to wait for missing data. Therefore, it has been proposed not to guarantee the order within a certain range.
Japanese Patent Laid-Open No. 2005-236961 JP 2005-150951 A

  As described so far, RLC and TCP are conventionally controlled independently, and RLC retransmits the same PDU at regular intervals when data loss occurs.

  However, even if the wireless state recovers before the TCP timer times out, the TCP timer times out because the retransmission interval at the time of data loss in RLC is a fixed time, resulting in a decrease in the transmission rate. That is not preferable.

  A communication apparatus according to an embodiment transmits data based on a first protocol to a partner apparatus as a transmission signal based on a second protocol lower than the first protocol, and confirms delivery of the transmission signal from the partner apparatus. A control unit that retransmits the transmission signal, a first timer that measures time until the data transmission rate based on the first protocol is reduced, and a transmission signal based on the second protocol. And a second timer for measuring the time until retransmission. The control unit changes the set time of the second timer according to the elapsed time of the first timer.

  The transmission method according to another embodiment includes a step of transmitting data based on a first protocol to a counterpart device as a transmission signal based on a second protocol lower than the first protocol, and the transmission signal from the counterpart device Retransmitting the transmission signal when no delivery confirmation is received. The time until the transmission signal is retransmitted is changed according to the passage of time until the data transmission rate based on the first protocol is lowered.

  If the wireless state recovers before the TCP timer times out, the transmission rate can be maintained without timing out the TCP timer.

  Embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same or corresponding reference numerals.

  A case where a transmission control protocol (TCP) and a radio link control protocol (RLC) are used will be described as an embodiment. However, in another embodiment, a protocol obtained by improving or modifying TCP or RLC that will be defined in the future may be used.

  Also, the case of the downlink in which data is transmitted from the radio network controller (RNC) to the user terminal (UE) will be mainly described, but the uplink of data transmitted from the user terminal (UE) to the radio network controller (RNC) The same applies to the case.

  FIG. 5 is a diagram illustrating a communication method in conventional RLC. For example, when the user terminal 10 enters a tunnel or a shadow of a building and the wireless state temporarily deteriorates (a state where the user terminal 10 enters a shaded portion in FIG. 5), the wireless network control device 20 sets the poll bit. Even if the PDU (SN = 0) 51 is transmitted with the signal set to ON, the PDU does not reach the user terminal 10 and a delivery confirmation (ACK) is not returned. Therefore, the transmission of the PDU 51 is repeated every certain time T by the retransmission timer.

  When the radio state of the user terminal 10 recovers (a state in which the user terminal 10 exits from the shaded portion in FIG. 5), the PDU 52 transmitted by the radio network control device 20 subsequently reaches the user terminal 10 and an acknowledgment (ACK) 53 is returned. .

  However, as shown in FIG. 5, since the RLC of the RNC 20 is controlled independently of the TCP, the TCP timer may already time out when the PDU 52 is retransmitted by the RLC. In that case, even if congestion does not necessarily occur, as described with reference to FIGS. 3A and 3B, there is a problem that the number of segments transmitted for congestion avoidance is reduced in the TCP layer.

  In order to eliminate or reduce such a problem, a communication method according to an embodiment includes transmitting data based on a transmission control protocol (TCP) to a partner apparatus as a transmission signal based on a radio link control protocol (RLC) lower than TCP. And retransmitting the transmission signal when no delivery confirmation for the transmission signal is received from the counterpart device. Then, the time until the transmission signal is retransmitted is changed according to the elapse of time until the data transmission rate based on the transmission control protocol is lowered. In one embodiment, “changing” is shorthand. In other embodiments, “modification” may include stretching. For example, when the time until the transmission signal is transmitted is changed a plurality of times in accordance with the passage of time until the data transmission rate based on the transmission control protocol is lowered, the data may be expanded at a part of the plurality of times. This will be described in more detail with reference to FIG.

  FIG. 6 is a diagram illustrating a communication method in RLC according to an embodiment. When the wireless quality is temporarily poor after entering the shadow of a tunnel or building, TCP drops the number of transmission segments if the TCP timer expires even if there is no congestion. Therefore, when the expiration of the TCP timer approaches, the set value of the RLC timer is changed (in this case, shortened) so that the RLC layer retransmits the PDU more frequently.

  In FIG. 6, the RNC 20 retransmits the PDU 51 every time the time T elapses by the RLC retransmission timer if the PDU 51 is transmitted and the ACK is not returned. However, the RNC 20 checks the TCP timer and changes (in this case, shortens) the time until the PDU is retransmitted (PDU 61 in FIG. 6) according to the elapsed time. This time is shortened by changing the set value of the RLC timer. As a result, the PDU can be retransmitted (PDU 62 in FIG. 6) and the ACK 63 is returned in the time from when the user terminal 10 leaves the bad wireless state (shaded part in FIG. 6) until the TCP timer expires. Can receive.

  In one embodiment, as shown in FIG. 6, the setting value of the RLC timer is gradually reduced from the default value to the shortened value before the expiration time when the elapsed time of the TCP timer exceeds the threshold value. Can do. In other embodiments, the default value may be shortened linearly from the shortened value. As described above, a method for shortening the setting value of the RLC timer can be selected according to the embodiment.

  RLC is a protocol terminated between a user terminal (UE) and a radio network controller (RNC), but TCP is a user terminal (UE) and a packet data network (more precisely, a server in the packet data network, etc. ). Therefore, although the user terminal (UE) implements both RLC and TCP, the radio network controller (RNC) implements only RLC and does not implement TCP. In the present embodiment, it is preferable that the RLC layer acquires the timer value of the TCP layer in order to shorten the PDU retransmission interval in the RLC layer as time elapses until the TCP layer times out.

  Therefore, in one embodiment, the TCP timer value of the TCP layer, that is, information regarding the time until the transmission rate of data based on TCP is reduced is received from the partner apparatus using the RLC control signal.

  FIG. 8 is a diagram illustrating a TCP timer notification method to the RNC according to an embodiment. In the RLC layer, there is a control signal called STATUS PDU for notifying the state. A TCP layer timer value can be transmitted using this control signal. In FIG. 8, when the user terminal 10 establishes a connection with the RNC 20 (step S81), the user terminal 10 transmits a STATUS PDU indicating a TCP timer value to the RNC 20 (step S83). Thereby, it is possible to acquire a TCP timer value in which the RNC is not mounted on itself.

  Further, when a change occurs in the TCP timer value (step S85), the user terminal 10 transmits a STATUS PDU indicating the changed TCP timer value to the RNC 20 (step S87). Thereby, even when the timer value is changed in the TCP layer, the TCP timer value in which the RNC is not mounted on itself can be acquired.

  Since STAUS PDU is used in this way, in one embodiment, as shown in FIG. 9, a new TCP timer can be added with SUFI Type = 8 in STATUS PDU. FIG. 9 is a diagram showing a STATUS PDU that can be used in the TCP timer notification method of FIG. Thus, by adding the SUFI type for notifying the TCP timer to the STATUS PDU, the user terminal 10 can notify the wireless network control device 20 of the TCP timer value.

  FIG. 10 is a flowchart illustrating a transmission method 100 in RLC according to an embodiment. In the transmission method 100, when there is data to be transmitted to a partner apparatus (for example, the user terminal 10 of FIG. 6), the communication apparatus (for example, the radio network control apparatus 20 of FIG. 6) first transmits the data as an RLC PDU. To do. At the same time, the RLC retransmission timer is started with a normal default value (step S102). Similarly, the TCP timer is also started using the set value of the TCP timer notified from the TCP layer (step S104).

  The communication device determines whether a delivery confirmation for the transmission data (RLC PDU) has been received from the counterpart device (step S106).

  If it is determined in step S106 that a delivery confirmation has been received (YES in step S106), the RLC timer started in step S102 is cleared (step S108), and the TCP timer started in step S104 is also cleared (step S110). ). Then, this transmission method ends.

  On the other hand, as a result of the determination in step S106, if a delivery confirmation has not been received (NO in step S106), it is determined whether the RLC retransmission timer started in step S102 has expired (step S112). In step S112, the process returns to step S106, and waits until delivery confirmation is obtained or the RLC retransmission timer expires.

  If the RLC retransmission timer expires as a result of the determination in step S112 (YES in step S112), the corresponding PDU is retransmitted (step S114), and the RLC retransmission timer is started again. At this time, it is determined whether X% (for example, 80%) or more of the TCP timer started in step S104 has elapsed (step S116). If X% or more has not elapsed (NO in step S116), the RLC retransmission timer defaults. The value is set and the RLC retransmission timer is started again (step S118). Then, the process returns to step S106 and waits until delivery confirmation is obtained or the RLC retransmission timer expires.

  On the other hand, as a result of the determination in step S116, if the TCP timer has exceeded X%, the RLC retransmission timer value is set to the default value Y% (for example, 50%) in order to confirm delivery before the TCP timer expires. Then, the RLC retransmission timer is started again (step S120). Then, the process returns to step S106 and waits until delivery confirmation is obtained or the RLC retransmission timer expires.

  In this way, by changing the PDU retransmission interval in the RLC layer according to the elapsed time of the TCP timer, it is possible to confirm delivery before the expiration of the TCP timer if the wireless state is recovered.

  In the transmission method 100 shown in FIG. 10, the setting value of the RLC retransmission timer is shortened from the default value to Y% depending on whether or not the TCP timer has elapsed X%. As described with reference, various modes are conceivable depending on the embodiment.

  It will be apparent to those skilled in the art that each step of the transmission method can be executed by a computer, a controller, a microprocessor, or the like.

  So far, the transmission method according to the embodiment has been described. Next, a mobile communication system according to an embodiment capable of implementing these transmission methods will be described. This mobile communication system includes a radio network control device and a user terminal.

  A radio network controller according to an embodiment transmits data based on a transmission control protocol (TCP) to a user terminal as a transmission signal based on a radio link control protocol (RLC) lower than TCP, and from the user terminal to the transmission signal When a delivery confirmation is not received, a control unit that retransmits the transmission signal, a TCP timer that measures time until the transmission rate of data based on TCP is reduced, and an RLC that measures time until a transmission signal based on RLC is retransmitted A retransmission timer. The control unit changes the set time of the RLC timer according to the elapsed time of the TCP timer.

  In addition, a user terminal according to another embodiment transmits data based on a transmission control protocol (TCP) to a radio network control device as a transmission signal based on a radio link control protocol (RLC) lower than TCP, and performs radio network control. When a delivery confirmation for a transmission signal is not received from the device, a control unit that retransmits the transmission signal, a TCP timer that measures time until the transmission rate of data based on TCP is reduced, and until a transmission signal based on RLC is retransmitted And an RLC retransmission timer for measuring the time. The control unit changes the set time of the RLC timer according to the elapsed time of the TCP timer.

  In one embodiment, “changing” is shorthand. In other embodiments, “modification” may include stretching. For example, when the time until the transmission signal is transmitted is changed a plurality of times in accordance with the passage of time until the data transmission rate based on the transmission control protocol is lowered, the data may be expanded at a part of the plurality of times.

  Such an embodiment will be described in more detail with reference to FIG. FIG. 11 is a block diagram illustrating a mobile communication system according to an embodiment. A mobile communication system 1100 illustrated in FIG. 11 includes a user terminal (UE) 100, a radio network controller (RNC) 200, and a core network 300.

  The user terminal 100 includes a downlink (DL) reception unit 151 that receives a reception signal in the downlink direction from the radio network control apparatus 200, and a downlink (DL) data processing unit 152 that processes the reception signal. In addition, the user terminal 100 has a higher-level application 170 that uses data included in the received signal. Further, the user terminal 100 transmits an uplink (UL) data processing unit 162 that processes the data generated and processed by the upper application 170, and transmits the processed data to the radio network controller 200 in the uplink direction. And an uplink (UL) transmission unit 163 that transmits the signal.

  The user terminal 100 includes a control unit 110 that controls the operation of the entire system and processes data, and a timer unit 130 that includes a TCP timer (not shown) and an RLC retransmission timer (not shown). The control unit 110 includes an RLC function unit 111, a timer monitoring / management unit 112, and a transmitted management unit 113. The operation of each part will be described in detail later.

  The radio network controller 200 includes a downlink (DL) reception unit 251 that receives a reception signal in the downlink direction from the core network 300, a downlink (DL) data processing unit 252 that processes the reception signal, and a processed reception. And a downlink (DL) transmission unit 253 that transmits a signal to the user terminal 100. Also, the radio network controller 200 includes an uplink (UL) reception unit 261 that receives an uplink direction reception signal received from the user terminal 100, and an uplink (UL) data processing unit 262 that processes the received reception signal. And an uplink (UL) transmission unit 263 that transmits the processed reception signal to the core network 300.

  The radio network control apparatus 200 includes a control unit 210 that controls the operation of the entire system and processes data, and a timer unit 230 that includes a TCP timer (not shown) and an RLC retransmission timer (not shown). The control unit 210 includes an RLC function unit 211, a timer monitoring / management unit 212, and a transmitted management unit 213. The operation of each part will be described in detail below.

  Here, processing in the downlink direction in which data is transmitted from the core network 300 toward the user terminal 100 will be described.

  First, in order to notify the RNC 200 of the setting value of the TCP timer, the UE 100 transmits the setting value of the TCP timer to the RNC 200 when the connection with the RNC 200 is set. Therefore, in the UE 100, the RLC function unit 111 included in the control unit 110 acquires the setting value of the TCP timer from the upper application unit 170 including the TCP layer, and as described with reference to FIGS. The PDU is transmitted to the RNC 200 via the UL transmitter 163.

  In the RNC 200, the UL reception unit 261 receives this STATUS PDU, the UL data processing unit 262 determines that the STATUS PDU notifies the TCP timer setting value, and the TCP timer setting value is included in the control unit 210. Notification to the unit 211. The timer monitoring / management unit 212 included in the control unit 210 receives the timer setting value from the RLC function unit 211 and sets it in a TCP timer (not shown) in the timer unit 230.

  Thereafter, when receiving data from the core network 300, the RNC 200 converts the data into a radio protocol and transmits the data to the UE 100 for transmission to the UE 100. The PDU transmitted at this time is stored in the transmitted management unit 213 included in the control unit 210, and the RLC function unit 211 transmits the RLC included in the timer unit 230 to the timer management unit 212 included in the control unit 210 at this timing. A timer (not shown) and a TCP timer (not shown) are started.

  When the RLC timer included in the timer unit 230 expires, the timer monitoring / management unit 212 included in the control unit 210 sends an expiration notification to the RLC function unit 211, and the RLC function unit 211 is stored in the transmitted management unit 213. A PDU resend request is issued and resent. When the TCP timer of the timer unit 230 exceeds a certain threshold value, the timer monitoring / managing unit 230 similarly sets the RLC retransmission timer of the timer management unit 230 to a shortened value.

  When receiving data, the UE 100 notifies the RLC function unit 111 of the control unit 110 that the DL data processing unit 152 has received the data. The RLC function unit 111 transmits a delivery confirmation signal (STATUS-ACK) to the RNC 200 via the UL transmission unit 163.

  The same applies to the processing in the uplink direction in which data is transmitted from the user terminal 100 to the core network 300 via the radio network control apparatus 200. However, since the upper application 170 knows the setting value of the TCP timer in the user terminal 100. The RLC function unit 111 included in the control unit 110 obtains the set value from a higher-level application and notifies the timer unit via the timer monitoring / management unit 112. It may be set to 130.

  As described above, the downlink communication in which data is transmitted from the radio network control apparatus to the user terminal is mainly described. However, the above embodiment is also applied to the uplink communication in which data is transmitted from the user terminal to the radio network control apparatus. It will be apparent to those skilled in the art that this can be done.

  Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Regarding the above embodiment, the following additional notes are disclosed.
(Appendix 1)
When the data based on the first protocol is transmitted to the counterpart device as a transmission signal based on the second protocol lower than the first protocol, and the delivery confirmation for the transmission signal is not received from the counterpart device, the transmission signal A control unit for retransmitting
A first timer for measuring time until the data transmission rate based on the first protocol is reduced;
A second timer for measuring a time until a transmission signal based on the second protocol is retransmitted,
The control unit changes a set time of the second timer according to an elapsed time of the first timer.
(Appendix 2)
The communication device according to appendix 1, wherein the control unit receives information related to a set value of the first timer from the counterpart device using a control signal of the second protocol.
(Appendix 3)
The communication device according to appendix 1, wherein the control unit transmits information related to a set value of the first timer to the counterpart device using a control signal of the second protocol.
(Appendix 4)
The communication apparatus according to appendix 1, wherein the first protocol is a transmission control protocol (TCP).
(Appendix 5)
The communication device according to attachment 1, wherein the second protocol is a radio link control protocol (RLC).
(Appendix 6)
The communication apparatus according to appendix 1, wherein the control unit changes the set time of the second timer in a stepwise manner in accordance with an elapsed time of the first timer.
(Appendix 7)
Transmitting data based on a first protocol to a counterpart device as a transmission signal based on a second protocol lower than the first protocol;
Retransmitting the transmission signal when not receiving a delivery confirmation for the transmission signal from the counterpart device,
A transmission method comprising: changing a time until the transmission signal is retransmitted according to a lapse of time until a data transmission rate based on the first protocol is lowered.

It is a figure which shows the example of a protocol stack used in a mobile communication system. It is a figure for demonstrating the slow start algorithm in TCP. It is a figure which shows the TAHOE system which is a corresponding system at the time of the data loss in TCP. It is a figure which shows the RENO system which is a corresponding system at the time of the data loss in TCP. It is a figure which shows the signal transmission method in RLC. It is a figure which shows the autonomous retransmission at the time of the data loss in RLC. It is a figure which shows the communication method in the conventional RLC. It is a figure which shows the communication method in RLC by one Embodiment. It is a graph which shows shortening of the RLC timer in the communication method of FIG. It is a figure which shows the TCP timer notification method to RNC by one Embodiment. It is a figure which shows STATUS PDU which can be utilized with the TCP timer notification method of FIG. 6 is a flowchart illustrating a transmission method in RLC according to an embodiment. It is a block diagram which shows the mobile communication system by one Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 User terminal 110 Control part 111 RLC function part 112 Timer monitoring / management part 113 Transmitted management part 130 Timer part 151 DL reception part 152 DL data processing part 162 UL data processing part 163 UL transmission part 170 Host application 200 Wireless network control apparatus 210 Control unit 211 RLC function unit 212 Timer monitoring / management unit 213 Transmitted management unit 230 Timer unit 251 DL reception unit 252 DL data processing unit 253 DL transmission unit 261 UL reception unit 262 UL data processing unit 263 UL transmission unit 300 Core network

Claims (5)

When the data based on the first protocol is transmitted to the counterpart device as a transmission signal based on the second protocol lower than the first protocol, and the delivery confirmation for the transmission signal is not received from the counterpart device, the transmission signal A control unit for retransmitting
A first timer for measuring time until the data transmission rate based on the first protocol is reduced;
A second timer for measuring a time until a transmission signal based on the second protocol is retransmitted,
The control unit changes a set time of the second timer according to an elapsed time of the first timer.   The communication device according to claim 1, wherein the control unit receives information related to a set value of the first timer from the counterpart device using a control signal of the second protocol.   The communication device according to claim 1, wherein the control unit transmits information related to a set value of the first timer to the counterpart device using a control signal of the second protocol.   The communication device according to any one of claims 1 to 3, wherein the control unit changes a set time of the second timer in a stepwise manner in accordance with an elapsed time of the first timer. Transmitting data based on a first protocol to a counterpart device as a transmission signal based on a second protocol lower than the first protocol;
Retransmitting the transmission signal when not receiving a delivery confirmation for the transmission signal from the counterpart device,
A transmission method comprising: changing a time until the transmission signal is retransmitted according to a lapse of time until a data transmission rate based on the first protocol is lowered.

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