JP2018125768A - Data transmission device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in a PDV to enhance measurement accuracy by achieving measurement of a phase offset (clock phase difference) of a clock with a small-scale circuit.SOLUTION: A phase measurement information extraction part 16 of a data transmission device 1 records a response packet reception time at a time point of receiving a signal from an opposite data transmission device 2, extracts phase measurement information from an RTP packet, and extracts a response time from the phase measurement information. A phase measurement information insertion part 12 records a response time at a time point when the RTP packet can be transmitted, and generates phase measurement information comprising a reference time, a reference packet reception time and the response time recorded by the phase measurement information insertion part 12 with the response time extracted by the phase measurement information extraction part 16 as the reference time and with the response packet reception time as the reference packet reception time. The phase measurement information insertion part 12 inserts the phase measurement information into the RTP packet. The RTP packet including real time data and the phase measurement information is transmitted to the opposite data transmission device 2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for transmitting data such as video, audio and waveform information associated with a clock via a network, and more particularly to a data transmission apparatus and program for transmitting data and clock information.

  2. Description of the Related Art Conventionally, a method of synchronizing clocks among a plurality of data transmission apparatuses in a system that transmits data such as video, audio, and waveform information (hereinafter referred to as real time data) associated with a clock via an IP network or the like. It has been known. Examples of the clock synchronization method include adaptive clock recovery, differential clock recovery, and time synchronization of NTP (Network Time Protocol).

[Adaptive clock recovery]
First, an adaptive clock recovery synchronization method will be described. Adaptive clock recovery is intended for a system that transmits data having a constant size at a constant clock interval (hereinafter referred to as a data interval) (see, for example, Patent Document 1).

  FIG. 11 is a block diagram showing a configuration example of a conventional data transmission apparatus that realizes clock synchronization by adaptive clock recovery. The data transmission apparatus 100 includes a packet receiving unit 102, a buffer unit 103, a local clock control unit 104, and a real time data extraction unit 105.

  In adaptive clock recovery, the data transmission apparatus 100 temporarily accumulates real-time data in the buffer unit 103 and reads out the real-time data from the buffer unit 103 at a data interval measured with a local clock.

  The packet receiving unit 102 receives an IP packet via the IP network 101 from a transmission-side data transmission device (not shown). Then, the packet receiving unit 102 extracts an RTP (Real-time Transport Protocol) packet from the IP packet, and stores the RTP packet in the buffer unit 103. In this case, the data transmission device on the transmission side transmits IP packets storing real-time data having a constant size at a constant data interval based on the local clock.

  The local clock control unit 104 monitors the accumulation amount (real-time data amount) of the RTP packet stored in the buffer unit 103, and controls the frequency of the local clock so that the accumulation amount is always within a certain range. . Specifically, the local clock control unit 104 increases the frequency of the local clock when the accumulation amount in the buffer unit 103 tends to increase, and conversely controls the decrease when it tends to decrease. Do. Thereby, the local clock on the receiving side can be synchronized with the local clock on the transmitting side.

  The real-time data extraction unit 105 reads RTP packets from the buffer unit 103 at a data interval based on the local clock controlled by the local clock control unit 104. Then, the real time data extraction unit 105 extracts real time data from the RTP packet and outputs the real time data.

  FIG. 11 shows an example in which the packet receiving unit 102 stores real-time data in the buffer unit 103 while being stored in the RTP packet, and the real-time data extracting unit 105 reads the state from the buffer unit 103 in the state of the RTP packet. . On the other hand, the packet receiving unit 102 may extract real time data from the RTP packet and store the real time data in the buffer unit 103.

  In general, since the IP network 101 has packet delay variation (PDV), even if the data transmission device on the transmission side transmits IP packets at regular intervals, the interval at which the data transmission device 100 on the reception side arrives. Is not constant. For this reason, the local clock output from the local clock control unit 104 of the data transmission apparatus 100 on the receiving side is affected by the PDV, and the phase noise increases.

  Therefore, the local clock control unit 104 adds a smoothing process or a low-pass filter process to the accumulation amount in the buffer unit 103 in order to reduce the influence of the PDV.

  Adaptive clock recovery is a technique for synchronizing clocks by utilizing the fact that the arrival interval of real-time data is constant. For this reason, although this method is easily affected by PDV or packet loss, there is an advantage that it is not necessary to transmit / receive special data for clock synchronization.

[Differential clock recovery]
Next, a differential clock recovery synchronization method will be described. In the differential clock recovery, in order to reduce the influence of PDV and packet loss, the clock is synchronized by using a reference clock (common clock) that can be commonly referred to between the transmission side and the reception side. (For example, see Patent Documents 2 and 3).

  The data transmission device on the transmission side uses the common clock to measure the clock used in the data transmission device, and sends the clock information such as the frequency deviation and phase deviation of the measured clock to the data transmission device on the reception side. Send.

  The data transmission device on the reception side receives the clock information from the data transmission device on the transmission side, and regenerates the clock of the data transmission device based on the received clock information and the common clock. As the common clock, for example, a GPS (Global Positioning System) clock, a physical layer clock in the IP network, or the like is used.

[NTP time synchronization]
As a clock synchronization method for reducing the influence of PDV without using a common clock, a method of directly measuring a clock time error between a transmission side and a reception side and correcting the clock is known. This technique is widely used for NTP (see, for example, Non-Patent Document 1).

  A method of measuring a clock time error in NTP is also used in IEEE 1688 PTP (see, for example, Patent Document 4). This method is used as a mechanism for synchronizing time information between data transmission apparatuses connected via an IP network (see, for example, Patent Document 5).

  NTP is a protocol for synchronizing a clock, and the phase of the clock is associated with the time measured by the clock. For this reason, the method of measuring the clock time error in the NTP can be used for the process of measuring the phase difference (phase offset) of the clock.

  Hereinafter, an example of measuring the phase offset between the local clock in the client data transmission apparatus (client apparatus) and the local clock in the server data transmission apparatus (server apparatus) will be described.

  FIG. 12 shows an NTP message sequence chart. First, the client device creates an inquiry packet and transmits it to the server device. The inquiry packet includes the inquiry packet transmission time (inquiry time (Tco)) measured by the client device using the local clock. As the inquiry time (Tco), for example, the value of a binary counter driven by a pulse of a local clock is used.

  When the server device receives the inquiry packet from the client device, the server device creates a response packet and transmits it to the client device. The response packet includes the inquiry time (Tco) included in the inquiry packet, the inquiry packet reception time (inquiry packet reception time (Tsr)) measured by the server device using the local clock, and the response packet transmission time. Time (response time (Tst)) is included.

  When the client device receives the response packet from the server device, the time when the response packet is received is recorded as a response packet reception time (Tcr) using the local clock of the client device.

Based on these four pieces of time information (inquiry time (Tco), inquiry packet reception time (Tsr), response time (Tst), and response packet reception time (Tcr)), the client device makes a round trip delay time (RTT). Is approximated by the following equation.
[Formula 1]
RTT≈ (Tcr−Tco) − (Tst−Tsr) (1)

Further, the client device assumes that the transmission delay of the received response packet is half of the round-trip delay time, and estimates the time (Tst ′) of the client device when the server device transmits the response packet using the following formula. .
[Formula 2]
Tst ′ = Tcr−RTT / 2 (2)

The client device obtains a value obtained by subtracting the response time (Tst) when the server device transmits the response packet from the time (Tst ′) of the client device when the server device transmits the response packet, and obtains this value as a phase offset Estimated as Toff. Thereby, the phase offset (Toff) is expressed by the following mathematical formula.
[Formula 3]
Toff = Tcr−RTT / 2−Tst (3)

  Thus, the phase offset is estimated based on the four pieces of time information (inquiry time (Tco), inquiry packet reception time (Tsr), response time (Tst), and response packet reception time (Tcr)). In such a method for measuring the phase offset in NTP, even when the packet delay time fluctuates, the phase offset can be accurately measured as long as the transmission delay of the inquiry packet and the response packet is approximately the same. .

JP 2002-368726 A US Pat. No. 7,492,732 JP 2012-80365 A JP 2010-19635 A JP2013-83451A

Mills, D., “Network Time Protocol Version 4: Protocol and Algorithms Specification”, RFC 5905, June 2010

  As described above, adaptive clock recovery does not require transmission / reception of special data for clock synchronization, but is susceptible to PDV. Differential clock recovery is not affected by PDV, but it is necessary to separately construct a means for transmitting a common clock.

  Further, the method of measuring the phase offset in NTP can alleviate the influence of PDV and does not need to transmit a common clock, but it is necessary to perform communication for inquiring time information. For this reason, each data transmission apparatus needs to have a communication function for transmitting / receiving a packet for transmitting time information for measuring a phase offset in addition to a communication function for transmitting / receiving a packet for transmitting real-time data. .

Real-time data transmission processing and time information transmission processing for measuring phase offset are performed using dedicated packets and protocols, respectively. For example, RTP (RFC3550) is used for real-time data transmission processing, and NTP (RFC5905) or IEEE1588 PTP is used for time information transmission processing. For RTP (RFC3550), refer to the following non-patent literature.
Schulzrinne, H., “RTP: A Transport Protocol for Real-Time Applications”, RFC 3550, July 2003

  As described above, in the method of measuring the phase offset in NTP, since it is necessary to implement processing functions of two types of protocols, there is a problem that the circuit scale increases when the data transmission apparatus is implemented as hardware. .

  In addition, when packets for measuring the phase offset are intermittently transmitted, the transmission timing of the packets for transmitting the real time data and the packets for measuring the phase offset may overlap. For this reason, there is a problem that transmission delay temporarily increases and PDV increases.

  In order to synchronize the local clock with high accuracy, it is effective to shorten the interval for measuring the phase offset. However, in order to shorten the measurement interval, it is necessary to increase the frequency of transmission of packets for measurement. For this reason, there is a problem that the network bandwidth is compressed and the PDV increases.

  Accordingly, the present invention has been made to solve the above-mentioned problems, and the object thereof is to realize measurement of a clock phase offset (clock phase difference) with a small-scale circuit and reduce an increase in PDV. An object of the present invention is to provide a data transmission device and a program capable of improving measurement accuracy.

  In order to solve the above-mentioned problem, the data transmission device according to claim 1 is a data transmission device that transmits a packet including data associated with a clock via a network, and transmits and receives the packet based on the clock. Time information about the time is generated as phase measurement information for measuring a clock phase difference between the data transmission apparatus and another data transmission apparatus connected to the network, and the phase measurement information is stored in a packet. A phase measurement information storage unit for generating a packet including the data and the phase measurement information; a packet transmission unit for transmitting the packet generated by the phase measurement information storage unit to the other data transmission device; A packet receiving unit that receives packets transmitted from other data transmission apparatuses, and the packet receiving unit A phase measurement information extraction unit that extracts other phase measurement information from the packet that has been transmitted, and a transmission / reception time point in the other data transmission device that is included in the other phase measurement information extracted by the phase measurement information extraction unit Based on the time information and the time information regarding the transmission / reception time in the data transmission device, the clock phase measurement unit that measures the clock phase difference, and the clock phase difference based on the clock phase difference measured by the clock phase measurement unit And a clock control unit for controlling.

  The data transmission device according to claim 2 is the data transmission device according to claim 1, wherein the phase measurement information generated by the phase measurement information storage unit is transmitted by the other data transmission device. The inquiry time indicating the time when the packet is received, the inquiry packet reception time indicating the time when the packet is received by the packet receiver, and the response time indicating the time when the packet can be transmitted by the packet transmitter It is characterized by comprising.

  According to a third aspect of the present invention, there is provided the data transmission device according to the second aspect, wherein the packet receiver receives another response indicating when the packet can be transmitted by the other data transmission device. Receiving the packet storing the other phase measurement information including time, and receiving the response packet when the phase measurement information extraction unit receives the packet by the packet reception unit based on the clock Set as time, extract the other phase measurement information from the packet received by the packet receiver, extract the other response time from the other phase measurement information, the phase measurement information storage unit, Based on the clock, the response time is set as the response time when the packet transmission unit can transmit the packet, and the phase measurement information extraction unit The extracted other response time is set as the inquiry time, the response packet reception time set by the phase measurement information extraction unit is set as the inquiry packet reception time, the inquiry time, the inquiry packet reception time And generating the phase measurement information including the response time, storing the phase measurement information in a packet, and generating a packet including the data and the phase measurement information.

  The data transmission device according to claim 4 is the data transmission device according to claim 1, wherein the phase measurement information generated by the phase measurement information storage unit is transmitted by the other data transmission device. Subtracting a response packet reception time indicating the time when the packet was received by the packet receiver from a reference time indicating the time when the packet was received and a response time indicating the time when the packet was transmitted by the packet transmitter It is comprised by the response waiting time obtained in this way, and the said response time.

  The data transmission device according to claim 5 is the data transmission device according to claim 4, wherein the packet receiver receives another response indicating when the packet can be transmitted by the other data transmission device. Receiving the packet storing the other phase measurement information including time, and receiving the response packet when the phase measurement information extraction unit receives the packet by the packet reception unit based on the clock Set as time, extract the other phase measurement information from the packet received by the packet receiver, extract the other response time from the other phase measurement information, the phase measurement information storage unit, Based on the clock, the time at which the packet can be transmitted by the packet transmission unit is set as the response time, and the phase meter is calculated from the response time. Subtracting the response packet reception time set by the information extraction unit, setting the result as the response waiting time, setting the other response time extracted by the phase measurement information extraction unit as the inquiry time, Generating the phase measurement information including the inquiry time, the response waiting time, and the response time, storing the phase measurement information in a packet, and generating a packet including the data and the phase measurement information. To do.

  The data transmission device according to claim 6 is the data transmission device according to any one of claims 1 to 5, wherein the phase measurement information storage unit stores the phase measurement information in an RTP extension header of an RTP packet. And storing and generating an RTP packet including the data and the phase measurement information.

  Furthermore, a program according to a seventh aspect causes a computer to function as the data transmission apparatus according to any one of the first to sixth aspects.

  As described above, according to the present invention, the measurement of the clock phase difference can be realized with a small circuit, and the increase in PDV can be mitigated and the measurement accuracy can be improved.

It is the schematic which shows the example of whole structure of the transmission system containing the data transmission apparatus by embodiment of this invention. It is a block diagram which shows the structural example of the data transmission apparatus by embodiment of this invention. It is a figure explaining the structural example of a RTP packet, and the structural example of phase measurement information. It is a figure which shows the message sequence chart for demonstrating a phase measurement information insertion part and a phase measurement information extraction part. It is a figure explaining the structural example of the phase measurement information of reception packet (alpha) 1 and transmission packet (beta) 1. It is a flowchart which shows the process example of a phase measurement information extraction part. It is a flowchart which shows the process example of a phase measurement information insertion part. It is a figure which shows the message sequence chart at the time of using response waiting time. It is a figure explaining the structural example of the phase measurement information of reception packet (alpha) 2 and transmission packet (beta) 2. It is a flowchart which shows the process example of the phase measurement information insertion part at the time of using response waiting time. It is a block diagram which shows the structural example of the conventional data transmission apparatus which implement | achieves clock synchronization by adaptive clock recovery. It is a figure which shows the message sequence chart of NTP.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is characterized in that, in a data transmission apparatus, time information for measuring a clock phase difference is multiplexed in a packet for transmitting data.

  As a result, it is not necessary to implement processing functions of two types of protocols for realizing data transmission processing and time information transmission processing, so that the circuit scale can be reduced. That is, the measurement of the clock phase difference can be realized with a small circuit. In addition, since the transmission timings of these packets do not overlap, there is no increase in PDV accompanying this, and the measurement accuracy of the clock phase difference can be improved.

  Hereinafter, a data transmission apparatus according to an embodiment of the present invention will be described using a transmission system in which two data transmission apparatuses are connected via an IP network as an example. The transmission system transmits real-time data from the first data transmission apparatus to the second data transmission apparatus, and transmits real-time data from the second data transmission apparatus to the first data transmission apparatus in the opposite direction. To transmit.

〔System configuration〕
First, a transmission system including a data transmission apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating an example of the overall configuration of a transmission system. The transmission system includes two data transmission apparatuses 1 and 2, and the data transmission apparatuses 1 and 2 are connected via an IP network 3.

  The data transmission apparatuses 1 and 2 operate in a master mode or a slave mode. In the example of FIG. 1, the data transmission device 1 operates in the master mode, and the data transmission device 2 operates in the slave mode. The data transmission device 2 that operates in the slave mode generates and outputs a clock that is synchronized with a clock that is input to the data transmission device 1 that operates in the master mode or a clock that is generated inside the data transmission device 1.

  The data transmission apparatus 1 inputs real-time data a associated with a clock and inputs a clock. Then, the data transmission device 1 creates an IP packet storing the real-time data a and clock information, and transmits the IP packet to the data transmission device 2 via the IP network 3.

  The data transmission device 2 receives the IP packet transmitted from the data transmission device 1 via the IP network 3, and extracts real-time data a and clock information from the IP packet. Then, the data transmission device 2 generates a clock based on the clock information, and outputs the real time data a and the clock.

  Further, the data transmission device 2 receives the real-time data b associated with the clock output from the data transmission device 2, creates an IP packet storing the real-time data b, and transmits the IP packet via the IP network 3. To the data transmission device 1.

  The data transmission apparatus 1 receives the IP packet transmitted from the data transmission apparatus 2 via the IP network 3, and extracts real-time data b from the IP packet. Then, the data transmission device 1 outputs real time data b.

  As a result, clock information, which is time information related to the clock input to the data transmission device 1, is transmitted to the data transmission device 2, and a clock synchronized with the clock of the data transmission device 1 is generated in the data transmission device 2. The real-time data a and b are transmitted and received as synchronized data.

[Data transmission equipment]
Next, the data transmission apparatuses 1 and 2 shown in FIG. 1 will be described in detail. FIG. 2 is a block diagram illustrating a configuration example of the data transmission apparatuses 1 and 2. The data transmission apparatuses 1 and 2 include an RTP packet creation unit 10, a buffer unit 11, a phase measurement information insertion (storage) unit 12, a packet transmission unit 13, a network interface 14, a packet reception unit 15, a phase measurement information extraction unit 16, A buffer unit 17, a real-time data extraction unit 18, a clock phase measurement unit 19, and a local clock control unit 20 are provided.

  As described above, the data transmission device 1 operates in the master mode, and the data transmission device 2 operates in the slave mode. As described above, the difference between the master mode and the slave mode is that the clock of the slave mode is synchronized with the clock on the basis of the clock of the master mode. That is, the data transmission device 2 operating in the slave mode generates a clock that is synchronized with the clock used by the data transmission device 1 operating in the master mode, and uses the clock.

  In FIG. 2, the difference between the data transmission apparatuses 1 and 2 is in the processing of the local clock control unit 20. The local clock control unit 20 provided in the data transmission apparatus 1 uses an input clock or an internally generated clock as a local clock. On the other hand, the local clock control unit 20 provided in the data transmission device 2 generates a clock synchronized with the local clock of the data transmission device 1 based on the clock phase difference between the data transmission devices 1 and 2, Used as a local clock. The components other than the local clock controller 20 perform the same processing between the data transmission apparatuses 1 and 2.

  The RTP packet creation unit 10 inputs real-time data to be transmitted associated with the clock input by the local clock control unit 20, creates an RTP packet storing the real-time data, and stores the RTP packet in the buffer unit 11. .

  The buffer unit 11 is a first-in first-out (FIFO) buffer, and holds the RTP packet until the RTP packet can be transmitted to the IP network 3.

  The phase measurement information insertion unit 12 inputs the response time and the response packet reception time from the phase measurement information extraction unit 16. The response time is the response time included in the phase measurement information received from the opposing data transmission devices 1 and 2, that is, transmission when the opposing data transmission devices 1 and 2 transmit the RTP packet including the phase measurement information. It is the time related to the time. The response packet reception time is the time when the RTP packet arrives at the packet receiver 15 or the phase measurement information extraction unit 16, that is, when the RTP packet including the phase measurement information is received from the opposing data transmission devices 1 and 2. This is the time related to the reception time.

  The phase measurement information insertion unit 12 waits until the RTP packet can be transmitted to the IP network 3, and inputs a transmission enable notification indicating that transmission is possible from the packet transmission unit 13. When the phase measurement information insertion unit 12 receives a transmission enable notification, the phase measurement information insertion unit 12 records the response time when the phase of the clock (local clock output by the local clock control unit 20) at that time (when transmission is possible) is measured. (Set). This response time is a time relating to a transmission time when the data transmission apparatuses 1 and 2 transmit an RTP packet including phase measurement information. The clock phase is measured by the clock phase measuring unit 19 by counting up the binary counter with the local clock.

  The phase measurement information insertion unit 12 sets the response time and response packet reception time input from the phase measurement information extraction unit 16 as an inquiry time and an inquiry packet reception time, respectively. Then, the phase measurement information insertion unit 12 generates phase measurement information including the inquiry time, the inquiry packet reception time, and the response time recorded by the phase measurement information insertion unit 12.

  Further, the phase measurement information insertion unit 12 reads the RTP packet from the buffer unit 11, inserts the phase measurement information into the RTP packet, and outputs the RTP packet to the packet transmission unit 13. Details of the phase measurement information insertion unit 12 will be described later.

(RTP packet and phase measurement information)
FIG. 3 is a diagram illustrating a configuration example of an RTP packet and a configuration example of phase measurement information. The RTP packet includes a UDP header, an RTP header, an RTP extension header, and an RTP payload. The example of FIG. 3 shows an example in which the phase measurement information is stored in the RTP extension header of the RTP packet.

  The phase measurement information includes an inquiry time, an inquiry packet reception time, and a response time. Three pieces of information of original timestamp, receive timestamp, and transmit timestamp in NTP are used as inquiry time, inquiry packet reception time, and response time.

  As described above, the phase measurement information insertion unit 12 generates phase measurement information including the inquiry time, the inquiry packet reception time, and the response time, and stores the phase measurement information in the RTP extension header area of the RTP packet.

  Note that the phase measurement information insertion unit 12 may store the phase measurement information in the first area of the RTP payload in the RTP packet or in another area.

  Here, the phase measurement information is preferably stored in the area of the RTP extension header. This is because the data transmission devices 1 and 2 can be connected to a conventional data transmission device based on adaptive clock recovery to form a data transmission system based on adaptive clock recovery. The phase measurement information is stored in the RTP packets transmitted by the data transmission apparatuses 1 and 2, but the conventional data transmission apparatus does not need this phase measurement information. In RTP, it is defined that a device that does not support an additional function using an RTP extension header ignores information of the RTP extension header. Therefore, even when the data transmission apparatuses 1 and 2 are connected as a master and the conventional data transmission apparatus is a slave, the conventional data transmission apparatus can normally read data other than the phase measurement information included in the RTP packet. And clock synchronization based on adaptive clock recovery.

  Furthermore, when the phase measurement information is not included in the extension header area of the RTP packet in the data transmission apparatuses 1 and 2, the data transmission apparatuses 1 and 2 have a function of performing clock synchronization based on adaptive clock recovery. to add. As a result, even when the conventional data transmission apparatus is connected as a master and the data transmission apparatuses 1 and 2 added with the clock synchronization function based on the adaptive clock recovery are connected as slaves, the clock synchronization based on the adaptive clock recovery is performed. be able to.

  Returning to FIG. 2, the packet transmission unit 13 monitors whether or not it is possible to transmit the RTP packet to the IP network 3. 12 is output.

  The packet transmission unit 13 receives the RTP packet from the phase measurement information insertion unit 12, adds an IP header and a MAC header to the RTP packet, and creates an IP packet addressed to the opposing data transmission apparatuses 1 and 2. Then, the packet transmitter 13 outputs the created IP packet transmission signal to the network interface 14.

  The network interface 14 receives a transmission signal from the packet transmission unit 13 and transmits the transmission signal to the opposing data transmission apparatuses 1 and 2 via the IP network 3. The network interface 14 receives signals transmitted from the opposing data transmission apparatuses 1 and 2 via the IP network 3 and outputs the received signals to the packet receiving unit 15.

  The packet receiver 15 receives a received signal from the network interface 14, extracts an RTP packet from the IP packet of the received signal, and outputs the RTP packet to the phase measurement information extractor 16. The RTP packet includes phase measurement information generated by the opposing data transmission apparatuses 1 and 2 and real-time data.

  When the RTP packet is input from the packet receiver 15, the phase measurement information extraction unit 16 records the response packet reception time when the phase of the clock at that time (the local clock output by the local clock controller 20) is measured. Note that the phase measurement information extraction unit 16 may record the response packet reception time when the phase of the clock at the time is measured at the time when the packet reception unit 15 inputs the reception signal. The response packet reception time indicates the time when the phase measurement information is received from the opposing data transmission apparatuses 1 and 2. The clock phase is measured by the clock phase measuring unit 19 by counting up the binary counter with the local clock.

  The phase measurement information extraction unit 16 extracts phase measurement information from the RTP packet and extracts a response time from the phase measurement information. Then, the phase measurement information extraction unit 16 outputs the extracted response time and the recorded response packet reception time to the phase measurement information insertion unit 12, and outputs the extracted phase measurement information and the recorded response packet reception time to the clock phase measurement unit. 19 output. Further, the phase measurement information extraction unit 16 stores the RTP packet in the buffer unit 17. Details of the phase measurement information extraction unit 16 will be described later.

  The RTP packet includes information that is not necessary for extracting real-time data in addition to information necessary for extracting real-time data. The phase measurement information extraction unit 16 may store the RTP packet after deleting various information such as phase measurement information that is not necessary for extracting real-time data in the buffer unit 17.

  Like the buffer unit 11, the buffer unit 17 is a first-in first-out buffer, and holds the RTP packet until the real-time data extraction unit 18 needs to extract real-time data from the RTP packet.

  The real-time data extraction unit 18 reads the RTP packet from the buffer unit 17, extracts real-time data from the RTP packet at the local clock timing output by the local clock control unit 20, and outputs the real-time data.

  The clock phase measurement unit 19 inputs the phase measurement information and the response packet reception time from the phase measurement information extraction unit 16, and extracts the inquiry time, the inquiry packet reception time, and the response time from the phase measurement information. Then, the clock phase measuring unit 19 calculates the clock of the data transmission apparatuses 1 and 2 opposite to the clock of the data transmission apparatuses 1 and 2 based on the inquiry time, the inquiry packet reception time, the response time, and the response packet reception time. Measure the clock phase difference between them. The clock phase difference can be measured based on these four pieces of time information, similarly to the processing described with reference to FIG. The clock phase measurement unit 19 outputs the clock phase difference to the local clock control unit 20.

  The clock phase measuring unit 19 inputs the local clock from the local clock control unit 20 and counts up the binary counter with the local clock, thereby measuring the clock phase. As a result, the phase measurement information insertion unit 12 records the phase of the clock at the time when the transmission enable notification is input as the response time and sets it as the phase measurement information. In addition, the phase measurement information extraction unit 16 records the phase of the clock when the RTP packet is input as the response packet reception time.

  The local clock control unit 20 inputs a clock, inputs a clock phase difference from the clock phase measurement unit 19, generates a local clock, and outputs the local clock to the clock phase measurement unit 19. The local clock control unit 20 outputs the local clock as a clock.

  Specifically, the local clock control unit 20 provided in the data transmission apparatus 1 operating in the master mode uses an input clock or an internally generated clock as a local clock.

  On the other hand, the local clock control unit 20 provided in the data transmission device 2 operating in the slave mode controls a PLL (Phase Locked Loop) based on the clock phase difference input from the clock phase measurement unit 19, Generate a local clock. The generated local clock is a clock synchronized with the clock of the data transmission device 1 operating in the master mode.

  Note that the local clock control unit 20 included in the data transmission device 2 operating in the slave mode adds the phase corresponding to the clock phase difference input from the clock phase measurement unit 19 to the input clock, thereby generating the local clock. You may make it produce | generate.

[Phase measurement information extraction unit 16]
Next, the phase measurement information extraction unit 16 shown in FIG. 2 will be described in detail. 4 is a diagram showing a message sequence chart for explaining the phase measurement information insertion unit 12 and the phase measurement information extraction unit 16, and FIG. 5 shows a configuration example of the phase measurement information of the reception packet α1 and the transmission packet β1. It is a figure explaining. FIG. 6 is a flowchart illustrating a processing example of the phase measurement information extraction unit 16. This is an example of the case where the phase measurement information is composed of the inquiry time, the inquiry packet reception time, and the response time, as shown in FIG.

  The data transmission device 1 receives a packet (see the received packet α1 in FIG. 5 (1)) including phase measurement information including the inquiry time, the inquiry packet reception time, and the response time c1 from the opposing data transmission device 2. Real-time data and phase measurement information are stored in the received packet α1.

  The phase measurement information extraction unit 16 of the data transmission apparatus 1 waits until the RTP packet (reception packet α1) arrives at the packet reception unit 15 or the phase measurement information extraction unit 16 (step S601). When the arrival of the RTP packet is detected (when the RTP packet is input from the packet reception unit 15), the phase measurement information extraction unit 16 records the clock phase at this time as the response packet reception time (step S602).

  The phase measurement information extraction unit 16 extracts the phase measurement information from the received RTP packet, and outputs the phase measurement information and the response packet reception time to the clock phase measurement unit 19 (step S603). Further, the phase measurement information extraction unit 16 extracts the response time c1 from the phase measurement information, and outputs the response time c1 and the response packet reception time to the phase measurement information insertion unit 12 (step S604).

  The phase measurement information extraction unit 16 stores the received RTP packet in the buffer unit 17 (step S605).

  In this way, the phase measurement information extraction unit 16 outputs the response time c1 included in the received phase measurement information and the response packet reception time that is the time when the received packet α1 is received to the phase measurement information insertion unit 12.

[Phase measurement information insertion unit 12]
Next, the phase measurement information insertion unit 12 shown in FIG. 2 will be described in detail. FIG. 7 is a flowchart illustrating a processing example of the phase measurement information insertion unit 12. This is an example of the case where the phase measurement information is composed of the inquiry time, the inquiry packet reception time, and the response time, as shown in FIG.

  The phase measurement information insertion unit 12 waits until the RTP packet can be transmitted to the IP network 3 (step S701). When the phase measurement information insertion unit 12 receives a transmission ready notification from the packet transmission unit 13 and detects that transmission is possible, the phase measurement information insertion unit 12 records the phase of the clock at this time as the response time c2 (step S702).

  The phase measurement information insertion unit 12 transfers (sets) the response time c1 (response time c1 included in the received phase measurement information) input from the phase measurement information extraction unit 16 to the inquiry time a2 (step S703). Further, the phase measurement information insertion unit 12 transcribes the response packet reception time input from the phase measurement information extraction unit 16 into the inquiry packet reception time b2 (step S704).

  The phase measurement information insertion unit 12 generates phase measurement information including the inquiry time a2 transcribed in step S703, the inquiry packet reception time b2 transcribed in step S704, and the response time c2 recorded in step S702 (step 702). S705).

  The phase measurement information insertion unit 12 inserts phase measurement information into the RTP packet read from the buffer unit 11 (step S706), and outputs the RTP packet to the packet transmission unit 13 (step S707).

  When dummy phase measurement information is stored in the RTP packet read from the buffer unit 11, the phase measurement information insertion unit 12 overwrites the phase measurement information generated in step S705. May be. In this case, the RTP packet creation unit 10 generates dummy phase measurement information, generates an RTP packet storing real-time data and dummy phase measurement information, and stores the RTP packet in the buffer unit 11. The phase measurement information insertion unit 12 overwrites the dummy phase measurement information in the RTP packet read from the buffer unit 11 with the phase measurement information generated in step S705.

  The data transmission device 1 transmits a packet including phase measurement information including the inquiry time a2, the inquiry packet reception time b2, and the response time c2 (see the transmission packet β1 in FIG. 5 (2)) to the opposing data transmission device 2. . Real-time data and phase measurement information are stored in the transmission packet β1.

  As described above, the response time c1 included in the received phase measurement information by the phase measurement information insertion unit 12 is the inquiry time a2, and the response packet reception time that is the time when the packet (received packet α1) is received is the inquiry packet reception time. As b2, the time when the packet (transmission packet β1) can be transmitted is set as the response time c2. Then, phase measurement information including inquiry time a2, inquiry packet reception time b2, and response time c2 is generated, and an RTP packet including real-time data and phase measurement information is generated.

  As described above, according to the data transmission apparatuses 1 and 2 according to the embodiment of the present invention, the phase measurement information extraction unit 16 records the response packet reception time when the signal is received from the opposing data transmission apparatuses 1 and 2. The phase measurement information is extracted from the RTP packet, and the response time is extracted from the phase measurement information.

  The phase measurement information insertion unit 12 records the response time when the RTP packet can be transmitted, sets the response time extracted by the phase measurement information extraction unit 16 as a reference time, and records it by the phase measurement information extraction unit 16 The response packet reception time is set as the inquiry packet reception time. Then, the phase measurement information insertion unit 12 generates phase measurement information including the inquiry time, the inquiry packet reception time, and the response time recorded by the phase measurement information insertion unit 12, and inserts the phase measurement information into the RTP packet. .

  Thereby, the RTP packet including real-time data and phase measurement information is transmitted to the opposing data transmission apparatuses 1 and 2.

  The clock phase measurement unit 19 includes an inquiry time, an inquiry packet reception time and a response time included in the phase measurement information extracted by the phase measurement information extraction unit 16, and a response packet reception time recorded by the phase measurement information extraction unit 16. Based on the above, the clock phase difference is measured.

  The local clock control unit 20 of the data transmission apparatus 1 operating in the master mode generates an input clock or an internally generated clock as a local clock. On the other hand, the local clock control unit 20 of the data transmission apparatus 2 operating in the slave mode controls the PLL based on the clock phase difference measured by the clock phase measurement unit 19 to generate a local clock.

  As a result, the slave mode local clock is synchronized with the master mode local clock.

  Therefore, the real-time data transmission process and the time information transmission process for measuring the clock phase difference can be realized simultaneously by one type of protocol, and the circuit scale can be reduced. That is, the measurement of the clock phase difference can be realized with a small circuit.

  In addition, since a packet for transmitting time information for measuring the clock phase difference is not necessary, the transmission timing of the packet for measuring the real time data and the packet for measuring the phase offset does not overlap, and the PDV can be increased. The measurement accuracy of the clock phase difference can be improved.

[Example of using response waiting time]
In the phase measurement information shown in FIG. 3, a response waiting time may be used instead of the inquiry packet reception time. The phase measurement information in this case is composed of an inquiry time, a response waiting time, and a response time. Further, the data transmission apparatuses 1 and 2 in this case are different in the processing of the phase measurement information insertion unit 12 and the clock phase measurement unit 19 in FIG. 2, and the processing of the other components is the same.

  The phase measurement information insertion unit 12 subtracts the response packet reception time input from the phase measurement information extraction unit 16 from the recorded response time to obtain a response standby time, and a phase measurement consisting of a reference time, a response standby time, and a response time Generate information.

  The clock phase measuring unit 19 extracts the response waiting time and the response time included in the phase measurement information input from the phase measurement information extracting unit 16, and subtracts the response waiting time from the response time to obtain the inquiry packet reception time. Then, the clock phase measurement unit 19 includes the inquiry time and response time included in the phase measurement information, the inquiry packet reception time obtained by the clock phase measurement unit 19, and the response packet reception time input from the phase measurement information extraction unit 16. , The clock phase difference is measured, and the clock phase difference is output to the local clock control unit 20. The clock phase measurement unit 19 measures the clock phase by counting up the binary counter with the local clock.

  Hereinafter, in the case where the phase measurement information is configured by the inquiry time, the response waiting time, and the response time, a processing example of the phase measurement information insertion unit 12 will be described in detail.

  FIG. 8 is a diagram illustrating a message sequence chart when the response waiting time is used, and FIG. 9 is a diagram illustrating a configuration example of the phase measurement information of the reception packet α2 and the transmission packet β2. FIG. 10 is a flowchart illustrating a processing example of the phase measurement information insertion unit 12 when the response waiting time is used.

  The data transmission device 1 receives a packet (see the received packet α2 in FIG. 9 (1)) including phase measurement information including the inquiry time, the response waiting time, and the response time c1 from the opposing data transmission device 2. Real-time data and phase measurement information are stored in the received packet α2.

  The phase measurement information extraction unit 16 of the data transmission apparatus 1 performs the same processing as the processing illustrated in FIG. 6, such as waiting until an RTP packet arrives at the packet reception unit 15 or the phase measurement information extraction unit 16. The phase measurement information extraction unit 16 outputs to the phase measurement information insertion unit 12 the response time c1 included in the received phase measurement information and the response packet reception time that is the time when the packet (reception packet α2) is received.

  The phase measurement information insertion unit 12 waits until the RTP packet can be transmitted to the IP network 3 (step S1001). When the phase measurement information insertion unit 12 receives a transmission enable notification from the packet transmission unit 13 and detects that transmission is possible, the phase measurement information insertion unit 12 records the phase of the clock at this time as the response time c2 (step S1002).

  The phase measurement information insertion unit 12 records the response waiting time d2 that is the result of subtracting the response packet reception time from the response time c2 (step S1003). That is, the response waiting time d2 is recorded as a phase increase from the phase of the clock at the response packet reception time to the phase of the clock at the response time c2.

  The phase measurement information insertion unit 12 transcribes the response time c1 (response time c1 included in the received phase measurement information) input from the phase measurement information extraction unit 16 to the inquiry time a2 (step S1004).

  The phase measurement information insertion unit 12 generates phase measurement information including the inquiry time a2 transcribed in step S1004, the response waiting time d2 recorded in step S1003, and the response time c2 recorded in step S1002 (step S1005). ).

  The phase measurement information insertion unit 12 inserts phase measurement information into the RTP packet read from the buffer unit 11 (step S1006), and outputs the RTP packet to the packet transmission unit 13 (step S1007).

  The data transmission device 1 transmits a packet including phase measurement information including the inquiry time a2, the response waiting time d2 and the response time c2 (see (2) transmission packet β2 in FIG. 9) to the opposing data transmission device 2. Real-time data and phase measurement information are stored in the transmission packet β2.

  As described above, the response time c1 included in the received phase measurement information is set as the inquiry time a2, the time when the packet (transmission packet β2) can be transmitted is set as the response time c2 by the phase measurement information insertion unit 12, and A result obtained by subtracting the response packet reception time, which is the time when the packet (reception packet α2) is received, from the response time c2 is set as the response waiting time d2. And the phase measurement information which consists of inquiry time a2, response waiting time d2, and response time c2 is produced | generated, and the RTP packet containing real-time data and phase measurement information is produced | generated.

  As described above, according to the data transmission apparatuses 1 and 2 of the embodiment of the present invention, when using the response waiting time, the phase measurement information insertion unit 12 records the response time when the RTP packet can be transmitted. Then, the response packet reception time recorded by the phase measurement information extraction unit 16 is subtracted from the response time to obtain the response waiting time. The phase measurement information insertion unit 12 uses the response time extracted by the phase measurement information extraction unit 16 as a reference time, the reference time, the response waiting time obtained by the phase measurement information insertion unit 12, and the phase measurement information insertion Phase measurement information including the response time recorded by the unit 12 is generated. Then, the phase measurement information insertion unit 12 inserts the phase measurement information into the RTP packet.

  Thereby, the RTP packet including real-time data and phase measurement information is transmitted to the opposing data transmission apparatuses 1 and 2.

  The clock phase measurement unit 19 subtracts the response waiting time from the response time included in the phase measurement information extracted by the phase measurement information extraction unit 16 to obtain the inquiry packet reception time. The clock phase measurement unit 19 receives the inquiry time and response time included in the phase measurement information, the inquiry packet reception time obtained by the clock phase measurement unit 19, and the reception of the response packet recorded by the phase measurement information extraction unit 16. The clock phase difference is measured based on the time. The local clock control unit 20 generates a local clock by the same processing shown in FIG.

  As a result, the slave mode local clock is synchronized with the master mode local clock.

  Therefore, as in the case of using the inquiry packet reception time, measurement of the clock phase difference can be realized with a small circuit, and the measurement accuracy can be improved by reducing the increase in PDV. In the phase measurement information, since the inquiry packet reception time and the response time are very close, the response waiting time becomes a small value, and the phase measurement information can be transmitted with a small number of bits as a whole.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical idea thereof. For example, in the above embodiment, the data transmission apparatuses 1 and 2 transmit RTP packets storing real-time data and phase measurement information. However, the present invention is not limited to RTP packets, and other types of RTP packets are stored. A packet may be transmitted.

  In addition, as described with reference to FIG. 4, the four pieces of information necessary for the data transmission device 2 to measure the clock phase difference are the three pieces of information included in the received phase measurement information (the inquiry to which the response time c1 is transcribed). The time a2, the inquiry packet reception time b2 in which the response packet reception time in the data transmission device 1 is transcribed, and the response time c2), and the response packet reception time in the data transmission device 2.

  In the embodiment of the present invention, the data transmission device 2 transmits the phase measurement information including the response time c1 and receives the phase measurement information including the inquiry time a2 to which the response time c1 is transcribed. Then, the data transmission device 2 extracts the inquiry time a2 that is the response time c1 from the received phase measurement information, and measures the clock phase difference. On the other hand, the data transmission device 2 may use the sequence number included in the header of the RTP packet instead of the response time c1 and transmit phase measurement information including the sequence number.

  In this case, when inserting the phase measurement information into the RTP packet, the phase measurement information insertion unit 12 of the data transmission device 2 extracts the sequence number from the RTP packet and generates phase measurement information including the sequence number. In addition, the phase measurement information insertion unit 12 associates the sequence number with the response time c1 and stores them in the index table. Then, the data transmission device 2 transmits phase measurement information.

  When the data transmission device 1 receives the phase measurement information from the data transmission device 2, the phase measurement information extraction unit 16 of the data transmission device 1 extracts the sequence number from the phase measurement information, and the phase measurement information insertion unit 12 receives the sequence number. Is transferred at inquiry time a2 to generate phase measurement information. Then, the data transmission device 1 transmits phase measurement information.

  When the data transmission device 2 receives the phase measurement information from the data transmission device 1, the phase measurement information extraction unit 16 of the data transmission device 2 extracts the sequence number from the phase measurement information and indexes the response time c1 corresponding to the sequence number. Read from the table. Thereby, the clock phase measuring unit 19 can measure the clock phase difference based on the four pieces of information.

  Note that a normal computer can be used as the hardware configuration of the data transmission apparatuses 1 and 2 according to the embodiment of the present invention. The data transmission devices 1 and 2 are configured by a computer having a volatile storage medium such as a CPU and a RAM, a nonvolatile storage medium such as a ROM, an interface, and the like.

  RTP packet creation unit 10, buffer unit 11, phase measurement information insertion unit 12, packet transmission unit 13, network interface 14, packet reception unit 15, phase measurement information extraction unit 16, buffer unit 17 provided in data transmission apparatuses 1 and 2 The functions of the real-time data extraction unit 18, the clock phase measurement unit 19 and the local clock control unit 20 are realized by causing the CPU to execute a program describing these functions.

  These programs are stored in the storage medium and read out and executed by the CPU. These programs can also be stored and distributed in a storage medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), optical disk (CD-ROM, DVD, etc.), semiconductor memory, etc. You can also send and receive.

1, 2, 100 Data transmission device 3, 101 IP network 10 RTP packet creation unit 11, 17, 103 Buffer unit 12 Phase measurement information insertion (storage) unit 13 Packet transmission unit 14 Network interface 15, 102 Packet reception unit 16 Phase measurement Information extraction unit 18, 105 Real-time data extraction unit 19 Clock phase measurement unit 20, 104 Local clock control unit

Claims (7)

In a data transmission device that transmits a packet including data associated with a clock via a network,
Based on the clock, time information related to the transmission / reception time of the packet is generated as phase measurement information for measuring a clock phase difference between the data transmission apparatus and another data transmission apparatus connected to the network. A phase measurement information storage unit for storing the phase measurement information in a packet and generating a packet including the data and the phase measurement information;
A packet transmission unit that transmits the packet generated by the phase measurement information storage unit to the other data transmission device;
A packet receiver for receiving a packet transmitted from the other data transmission device;
A phase measurement information extraction unit that extracts other phase measurement information from the packet received by the packet reception unit;
Based on the time information related to the transmission / reception time in the other data transmission device and the time information related to the transmission / reception time in the data transmission device included in the other phase measurement information extracted by the phase measurement information extraction unit A clock phase measurement unit for measuring the phase difference;
A clock control unit for controlling the clock based on the clock phase difference measured by the clock phase measurement unit;
A data transmission device comprising: The data transmission device according to claim 1,
The phase measurement information generated by the phase measurement information storage unit is
An inquiry time indicating when the packet can be transmitted by the other data transmission device, an inquiry packet reception time indicating a time when the packet is received by the packet receiver, and the packet by the packet transmitter A data transmission device comprising a response time indicating a point in time at which transmission becomes possible. The data transmission device according to claim 2,
The packet receiver
Receiving the packet storing the other phase measurement information including another response time indicating the time when the packet can be transmitted by the other data transmission device;
The phase measurement information extraction unit
Based on the clock, the time when the packet is received by the packet receiver is set as a response packet reception time, and the other phase measurement information is extracted from the packet received by the packet receiver, The other response time is extracted from other phase measurement information,
The phase measurement information storage unit
Based on the clock, the time when the packet can be transmitted by the packet transmission unit is set as the response time, and the other response time extracted by the phase measurement information extraction unit is set as the inquiry time. The response packet reception time set by the phase measurement information extraction unit is set as the inquiry packet reception time, and the phase measurement information including the inquiry time, the inquiry packet reception time, and the response time is generated, A data transmission apparatus characterized by storing phase measurement information in a packet and generating a packet including the data and the phase measurement information. The data transmission device according to claim 1,
The phase measurement information generated by the phase measurement information storage unit is
The packet receiving unit receives the packet from the inquiry time indicating when the other data transmission device can transmit the packet, and the response time indicating when the packet transmitting unit can transmit the packet. A data transmission apparatus comprising: a response waiting time obtained by subtracting a response packet reception time indicating the received time, and the response time. The data transmission apparatus according to claim 4, wherein
The packet receiver
Receiving the packet storing the other phase measurement information including another response time indicating the time when the packet can be transmitted by the other data transmission device;
The phase measurement information extraction unit
Based on the clock, the time when the packet is received by the packet receiver is set as a response packet reception time, and the other phase measurement information is extracted from the packet received by the packet receiver, The other response time is extracted from other phase measurement information,
The phase measurement information storage unit
Based on the clock, the time when the packet can be transmitted by the packet transmission unit is set as the response time, and the response packet reception time set by the phase measurement information extraction unit is subtracted from the response time. The result is set as the response waiting time, the other response time extracted by the phase measurement information extraction unit is set as the inquiry time, and the inquiry time, the response waiting time, and the response time are included. A data transmission device that generates phase measurement information, stores the phase measurement information in a packet, and generates a packet including the data and the phase measurement information. In the data transmission device according to any one of claims 1 to 5,
The phase measurement information storage unit
A data transmission apparatus, wherein the phase measurement information is stored in an RTP extension header of an RTP packet, and an RTP packet including the data and the phase measurement information is generated.   The program for functioning a computer as a data transmission apparatus as described in any one of Claim 1-6.

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