JP2009005070A - Communication system, communication method, and communication program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To synchronize time between each terminal device connected to a user interface of each subscriber-side communication device having a different connection distance in-between a station-side communication device. <P>SOLUTION: A communication system is provided with a time-stamp notification part, which notifies a first time-stamp being time information indicating time of a first counter possessed by a station-side communication device with a time-synchronization frame for propagating the first time-stamp from the station-side communication device to a subscriber-side communication device, an RTT notification part, which notifies RTT (Round Trip Time) being time information indicating round-trip propagation time between the station-side communication device and the subscriber-side communication device with an RTT notification frame for propagating the RTT from the station-side communication device to the subscriber-side communication device, and a time-stamp correction part that corrects a second time-stamp being time information indicating time of a second counter synchronized with time indicated by the first time-stamp notified with the time-synchronization frame on the basis of the RTT notified with the RTT notification frame. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication method, a communication method, and a communication program in which a subscriber side communication device communicates with a station side communication device, and more particularly to a time synchronization technique in a subscriber side communication device.

  As a conventional access network, a GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system is known (see, for example, Non-Patent Document 1). In this GE-PON system, a plurality of subscriber side communication devices and a station side communication device are connected by a fiber optic cable cable via a star coupler, and a plurality of subscriber side communication devices are connected to a single station side. Since the communication device is shared, it is economical.

IEEE (Institut of Electrical and Electronics Engineers) 802.3ah-2004 (427, 428 pages)

  In the GE-PON system disclosed in Non-Patent Document 1, subscriber-side communication devices having different connection distances are mixed, and the counters in the subscriber-side communication devices are shifted by a communication time corresponding to each connection distance. It is synchronized with the counter in the side communication device. The station side communication device measures the connection distance of each subscriber communication device, and corrects in advance the time information to be transmitted to the station side communication device for each subscriber communication device based on the measured distance information. Notice. Therefore, the subscriber communication device is not provided with means for synchronizing with the counter of the station side communication device. On the other hand, when a control device is connected as a terminal device, the same time of the sensor information between the control devices and the same time are required when recording the event occurrence of the control target and the control device. For example, if a terminal device such as a sensor or an actuator is connected to the user interface of each subscriber side communication device and synchronization is performed by a counter in each subscriber side communication device, the time will be different between the terminal devices. was there.

  The present invention has been made to solve the above-described problems, and each terminal device connected to the user interface of each subscriber-side communication device having a different connection distance, such as a GE-PON system, in the communication method. The purpose is to achieve time synchronization with a simple configuration and method.

  The communication method according to the present invention is for time synchronization in which a first time stamp, which is time information indicating the time of a first counter included in a station side communication device, is propagated from the station side communication device to a subscriber side communication device. A time stamp notifying unit for notifying by a frame, and RTT (Round Trip Time), which is time information indicating a round trip propagation time between the station side communication device and the subscriber side communication device, is sent from the station side communication device to the Based on the RTT notification unit that notifies the RTT notification frame propagated to the subscriber side communication device, and the first time stamp notified by the time synchronization frame based on the RTT notified by the RTT notification frame And a time stamp correction unit that corrects a second time stamp that is time information indicating the time of the second counter synchronized with the time.

  The present invention provides time synchronization between terminal devices connected to the user interface of each subscriber-side communication device having a different connection distance to the station-side communication device in the communication system, and prevents temporal fluctuations in transmission timing. However, stable time synchronization can be realized.

Embodiment 1 FIG.
In the communication system according to Embodiment 1 of the present invention, in a time stamp correction unit provided in a subscriber side communication device, the round-trip propagation time between the subscriber side communication device and the station side communication device is RTT, and each connection distance For notifying the TS and the terminal device of a time stamp indicating the time of the second counter in the subscriber side communication device synchronized with the first counter in the station side communication device with a shift of the propagation time corresponding to When the time stamp is expressed as TS_sync, TS_sync is synchronized with the first counter in the station side communication device by correcting the TS using the RTT notified from the station side communication device according to the relational expression TS_sync = TS + RTT / 2. The time information is obtained. Thereby, time synchronization can be taken between the terminal devices connected to the user interfaces of the subscriber side communication devices having different connection distances.

  FIG. 1 is a block diagram showing a communication system according to Embodiment 1 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 1, a station side communication device (OLT: Optical Line Terminal) 1 is connected to a subscriber side communication device (ONU: Optical Network Unit) 2 via an optical fiber cable 101 and an optical coupler 102, and is connected to an IEEE (Institut). A GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system that is compliant with of Electrical and Electronics Engineers (802.3ah) is configured. A terminal device 4 such as a sensor or an actuator is connected to the user side of the ONU 2.

  In FIG. 1, the OLT 1 is an optical / electrical conversion unit 11 that performs photoelectric conversion as an optical interface on the PON side, and a frame extraction unit 12 that extracts an upstream PON control frame from an upstream frame in the upstream direction from the ONU 2 to the OLT 1. Using the extracted upstream PON control frame information, a downstream PON control frame from OLT 1 to ONU 2 is generated, and OLT PON control unit 13 that performs upstream burst control is defined by IEEE 802.3ah. Local timer unit 14 that manages a first counter necessary for PON control, MUX unit 15 that multiplexes various downlink frames, and time stamp insertion as a time stamp notification unit that inserts a first time stamp into a specific frame RTT (Round Trip Time) in part 16, ONU2 RTT notification frame generator 17 as RTT notification unit that generates a RTT notification frame for notifying to and includes an interface unit 18 for providing an electrical interface on the network side.

  In FIG. 1, an ONU 2 includes an optical / electrical conversion unit 21 that performs photoelectric conversion as an optical interface on the PON side, a frame extraction unit 22 that extracts various frames from downstream downlink frames, and an extracted downstream PON control frame. The ONU PON control unit 23 that generates an uplink PON control frame in the upstream direction, the local timer unit 24 that manages the second counter necessary for PON control, and the MUX unit that multiplexes various uplink frames 25, a time stamp insertion unit 26 that inserts a second time stamp into a specific frame, a time stamp correction unit 27 that generates time information synchronized with the counter of the OLT 1 based on the RTT received from the OLT 1, and a downstream downlink frame Provides a downstream buffer unit 28 for storing data and a user-side electrical interface. And an interface unit 29 as a user interface for.

  Next, the operation will be described. A plurality of ONUs 2 connected to the OLT 1 via the optical fiber cable 101 and the optical coupler 102 are located at different distances from the OLT 1. In the GE-PON system defined by IEEE 802.3ah, a time stamp for embedding an RTT, which is a round trip propagation time corresponding to the distance between OLT 1 and ONU 2, in an upstream PON control frame and a downstream PON control frame for communication between OLT 1 and ONU 2 Measure using

  First, the operation of RTT measurement will be described. Each of the OLT 1 and each ONU 2 has a 32-bit counter in the local timer unit 14 and the local timer unit 24. When the main signal transfer rate is 1.25 Gbps (Giga bit per second), these counters count up every 16 ns. In the OLT 1, the local timer unit 14 automatically counts up the first counter, and when transmitting the downstream PON control frame as the time synchronization frame, the time stamp inserting unit 16 enters the time stamp area in the downstream PON control frame. The value of the first counter is set as the first time stamp (OLT time t0). On the other hand, when the ONU 2 receives the downlink PON control frame as the time synchronization frame, the local timer unit 24 sets the value of the first time stamp in the second counter (ONU time t0). As a result, the first counter of the OLT 1 becomes the main and the second counter of the ONU 2 becomes the subordinate, and synchronization is performed with a shift by the propagation time of the downstream PON control frame as the time synchronization frame.

  In the ONU 2, when transmitting the upstream PON control frame, the time stamp insertion unit 26 sets the value of the second counter of the local timer unit 24 in the time stamp area in the upstream PON control frame (ONU time t1). In the OLT 1, when an upstream PON control frame is received, the value of the time stamp area in the upstream PON control frame (ONU time t1) and the value of the first counter of the local timer unit 14 at the time of reception (OLT time t2) The OLT PON control unit 13 measures RTT (RTT = (OLT time t2−OLT time t0) − (ONU time t1−ONU time t0) = t2−t1). The OLT 1 corrects the variation of the RTT by periodically executing a procedure using the upstream PON control frame and the downstream PON control frame.

According to the procedure using the downstream PON control frame in the RTT measurement, the first counter of the OLT 1 and the second counter of the ONU 2 are synchronized with a shift of the propagation time of the time synchronization frame equal to RTT / 2. It will be. The RTT is managed by the OLT PON control unit 13 in the OLT 1. Accordingly, the RTT notification frame generated by the RTT notification frame generation unit 17 is used to periodically notify each ONU 2 of the RTT information corresponding to each ONU 2 from the OLT 1. In each ONU 2, the time stamp correction unit 27 calculates the third time according to the following equation (1) from the second time stamp TS, which is time information indicating the value of the second counter of the own device, and the notified RTT. By calculating the time stamp TS_sync, it is possible to obtain time information synchronized with the first counter in the OLT 1.
TS_sync = TS + RTT / 2 (1)

  In this way, the third time stamp TS_sync obtained by the ONU 2 is notified to the terminal device 4 connected to the user interface unit 29 of the own device, and the counter of the terminal device 4 performs time synchronization based on the notified time information. Thus, time synchronization can be established between the terminal devices 4 connected to different ONUs 2 at the same time synchronized with the first counter in the OLT 1.

  As described above, in the communication method according to the first embodiment of the present invention, in the GE-PON system, the time stamp correction unit 26 provided in the ONU 2 sends the round-trip propagation notified from the OLT 1 by the relational expression TS_sync = TS + RTT / 2. By correcting the second time stamp TS indicating the time of the second counter in the ONU 2 using the time RTT, the third time stamp TS_sync for notifying the terminal device 4 is obtained. Thereby, time synchronization can be taken between the terminal devices 4 connected to the user interfaces of the ONUs 2 having different connection distances.

  Incidentally, IEEE 1588 called “Precision Time Protocol” was standardized in 2002 as a communication method for realizing time synchronization with high accuracy on the order of sub-milliseconds on Ethernet (registered trademark). In the communication system based on IEEE 1588, time synchronization is performed by exchanging messages between a master clock function unit and a slave clock function unit arranged on a network. Furthermore, in the communication method according to IEEE 1588, the variation of the delay amount is corrected by the boundary clock function unit in which the master clock function unit and the slave clock function unit are arranged in the input / output unit of the switch in which the built-in buffer varies the delay amount. Thus, time synchronization is performed. If a communication method based on IEEE 1588 is used, time synchronization can be performed by a terminal device on the GE-PON system. However, in this case, it is necessary to additionally install a master clock function unit, a slave clock function unit, and a boundary clock function unit in both the OLT and the ONU, which makes the configuration complicated and further increases the number of message exchanges. To be complicated. On the other hand, according to the communication system according to the first embodiment of the present invention, as described above, time synchronization can be realized with the same accuracy with a simple configuration and procedure as compared with the communication system according to IEEE 1588. There is an effect.

Embodiment 2. FIG.
In the communication system according to the second embodiment of the present invention, a time stamp correction unit provided in a time synchronization unit connected to a user interface of a subscriber side communication device is used between a subscriber side communication device and a station side communication device. A time stamp indicating the time of the second counter in the subscriber-side communication device synchronized with the first counter in the station-side communication device with a round-trip propagation time of RTT shifted by a propagation time corresponding to each connection distance Is expressed as TS, the delay amount corresponding to the transfer time between the subscriber side communication device and the time synchronization unit is expressed as α, and the time stamp for notifying the terminal device is expressed as TS_sync, the relational expression of TS_sync = TS + RTT / 2 + α By correcting the TS using the RTT notified from the station side communication device, TS_sync is synchronized with the first counter in the station side communication device. It is to be requested as information. As a result, even in an existing subscriber side communication device that does not include a time stamp correction unit, between each terminal device connected to the user interface of each subscriber side communication device having a different connection distance via the time synchronization unit. Time synchronization can be taken.

  FIG. 2 is a block diagram showing a communication system according to Embodiment 2 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 2, 3 is a time synchronization unit, and 103 is an electric cable. Other configurations are the same as those according to the first embodiment shown in FIG. However, the ONU 2a is an IEEE 802.3ah-compliant subscriber-side communication device having an existing configuration in which the time stamp correction unit 26 shown in FIG. 1 is omitted. The terminal device 4 is connected to the user side of the time synchronization unit 3.

  In FIG. 2, the OLT 1 is a photoelectric conversion unit 11 that performs photoelectric conversion as an optical interface on the PON side, and a frame extraction unit 12 that extracts an upstream PON control frame from an upstream upstream frame from the ONU 2 to the OLT 1. Using the extracted upstream PON control frame information, a downstream PON control frame from OLT 1 to ONU 2 is generated, and OLT PON control unit 13 that performs upstream burst control is defined by IEEE 802.3ah. Local timer unit 14 that manages a first counter necessary for PON control, MUX unit 15 that multiplexes various downlink frames, and time stamp insertion as a time stamp notification unit that inserts a first time stamp into a specific frame RTT (Round Trip Time) in part 16, ONU2 RTT notification frame generator 17 as RTT notification unit that generates a RTT notification frame for notifying to and includes an interface unit 18 for providing an electrical interface on the network side.

  In FIG. 2, the time synchronization unit 3 includes an interface unit 31 connected to the user interface of the ONU 2a, a frame extraction unit 32 for extracting various frames from downlink frames in the downlink direction, and a second counter necessary for time synchronization. A local timer unit 33 that manages the time, a time stamp correction unit 34 that generates time information synchronized with the OLT 1 based on the RTT received from the OLT 1, and an interface unit 35 for connecting the terminal device 4.

  Next, the operation will be described. The RTT notification frame generation unit 17 of the OLT 1 stores the RTT information for each ONU 2a obtained by the above-described RTT measurement as MPCP (Multi-Point Control Protocol) processing defined in IEEE 802.3ah in a frame, and generates this The RTT notification frame is periodically inserted into the buffer in the MUX unit 15. The frame read from the buffer in the MUX unit 15 is given a first time stamp, which is time information indicating the time of the first counter of the local timer unit 14, by the time stamp insertion unit 16, and the time It is distributed toward each ONU 2a also serving as a synchronization frame. In each ONU 2a, the frame is handled in the same manner as a normal user frame, and is transferred to the time synchronization unit 3 in the subsequent stage.

In the time synchronization unit 3 connected to the user side of the ONU 2a, the second counter of the local timer unit 33 counts up at the same clock frequency as the first counter of the local timer unit 14 of the OLT 1. The frame extraction unit 32 extracts a first time stamp every time a frame for time synchronization addressed to the own device is received, sets the second time stamp in the second counter of the own device, and synchronizes the time. Further, in the time stamp correction unit 34, the second time stamp TS, which is time information indicating the value of the second counter, is obtained from the RTT information notified in the RTT notification frame and the ONU 2a to the time synchronization unit 3. The third time stamp TS_sync is obtained as time information synchronized with the first counter in the OLT 1 by performing correction by the following equation (2) using the delay amount α.
TS_sync = TS + RTT / 2 + α (2)

  The delay amount α may be fixedly given to the time synchronization unit 3, or may be registered in the OLT 1, stored in a time synchronization frame, and distributed to the time synchronization unit 3. Also good.

  In this way, the third time stamp TS_sync obtained by the time synchronization unit 3 is notified to the terminal device 4 connected to the user interface unit 35 of the own device, and the counter of the terminal device 4 uses the notified time information. By taking time synchronization, time synchronization can be achieved at the same time synchronized with the first counter in the OLT 1 between the terminal devices 4 connected to different ONUs 2a via the time synchronization unit 3.

  In the local timer unit 33 of the time synchronization unit 3, it is desirable that the time correction of the second counter for the first time synchronization is performed before the user communication is started. This is to prevent the time synchronization frame from being buffered in the downstream buffer 28 of the ONU 2a due to the presence of the user frame, and the fluctuation of the delay amount α from occurring. Further, after the communication is started, a time synchronization frame is periodically transmitted from the OLT 1. The time synchronization unit 3 compares the value of the first time stamp in the received time synchronization frame with the value of the second counter of its own device when the time synchronization frame is received, and the difference between the compared times is When the set threshold value is exceeded, the time synchronization frame is handled as being buffered in the ONU 2a, and the value of the first time stamp is not taken into the second counter. Thereby, it is possible to detect arrival fluctuation of the time synchronization frame caused by the user frame, and an effect of improving the accuracy of time synchronization can be expected. In addition, when the above difference is equal to or less than the above threshold, the time of the second counter may be finely adjusted stepwise by decreasing the difference in a plurality of times.

  In addition, in order to prevent delay fluctuation of the time synchronization frame in a state where the user frame and the time synchronization frame are mixed, the time synchronization frame is transferred to the time synchronization unit 3 as shown in FIG. The ONU 2a as the first subscriber-side communication device for performing communication and the ONU 2a as the second subscriber-side communication device that transmits and receives user frames are separated and connected to the terminal device 4 in parallel. Also good. By doing so, only the time synchronization frame is transmitted to the ONU 2a for time synchronization, and congestion can be avoided. Therefore, highly accurate time synchronization is performed in the second counter of the time synchronization unit 3. It becomes feasible.

  As described above, in the communication method according to the second embodiment of the present invention, in the GE-PON system, the time stamp correction unit 34 provided in the time synchronization unit 3 connected to the user interface of the ONU 2a has the function TS_sync = TS + RTT / 2 + α. In order to notify the terminal device 4 by correcting the second time stamp TS indicating the time of the second counter in the time synchronization unit 3 using the round-trip propagation time RTT notified from the OLT 1 by the relational expression The third time stamp TS_sync is obtained. As a result, even if the existing ONU 2a does not include the time stamp correction unit 27, time synchronization is established between the terminal devices 4 connected to the user interfaces of the ONUs 2a having different connection distances via the time synchronization unit 3. Can do.

  As described above, in the first and second embodiments of the present invention, the case where the present invention is applied to the GE-PON system has been described. Needless to say, however, the application system is not limited to this, and the frame propagation time is not limited to this. As long as communication is performed between a plurality of different slave communication devices and the main communication device, it can be applied to any system such as optical or electrical wired communication or wireless communication, and has the same effect. .

  Further, the communication method in the GE-PON system according to the first and second embodiments of the present invention is realized by software processing using a communication program executed by a microcomputer or the like provided in the OLT 1, ONU 2, or time synchronization unit 3. You may do it.

Configuration diagram showing a communication system according to Embodiment 1 of the present invention Configuration diagram showing a communication system according to Embodiment 2 of the present invention Configuration diagram showing a communication system according to Embodiment 2 of the present invention

Explanation of symbols

1 Station side communication device 2, 2 a Subscriber side communication device 3 Time synchronization unit 14, 24, 33 Local timer unit 15 RTT notification frame generation unit 16 Time stamp insertion unit 27, 34 Time stamp correction unit 29, 35 Interface unit

Claims (8)

A time stamp notifying unit for notifying a first time stamp, which is time information indicating the time of a first counter included in the station side communication device, with a time synchronization frame propagating from the station side communication device to the subscriber side communication device When,
RTT notification that propagates RTT (Round Trip Time), which is time information indicating the round-trip propagation time between the station-side communication device and the subscriber-side communication device, from the station-side communication device to the subscriber-side communication device An RTT notifying unit for notifying with a frame,
Based on the RTT notified in the RTT notification frame, the second time is time information indicating the time of the second counter synchronized with the time indicated by the first time stamp notified in the time synchronization frame. A time stamp correction unit for correcting the stamp,
A communication system characterized by comprising: A local timer unit that synchronizes the time of the second counter of the subscriber side communication device with the time indicated by the first time stamp notified in the time synchronization frame;
The time stamp correction unit represents a third time stamp, which is time information notified through the user interface of the subscriber side communication device, as TS_sync, and indicates the time of the second counter synchronized with the local timer unit. When the second time stamp as the time information to be shown is expressed as TS,
TS_sync = TS + RTT / 2
The communication method according to claim 1, wherein the third time stamp is obtained by the relational expression: A local timer unit that synchronizes the time of the second counter included in the time synchronization unit connected to the user interface of the subscriber side communication device at the time indicated by the first time stamp notified in the time synchronization frame; With
The time stamp correction unit represents a third time stamp, which is time information notified through the user interface of the time synchronization unit, as TS_sync, and indicates a time of the second counter synchronized with the local timer unit When the second time stamp as information is represented by TS and the delay amount from the subscriber side communication device to the time synchronization unit is represented by α,
TS_sync = TS + RTT / 2 + α
The communication method according to claim 1, wherein the third time stamp is obtained by the relational expression:   The local timer unit synchronizes the time of the second counter before the start of communication by the user frame, and after the start of communication, the time indicated by the first time stamp periodically notified by the time synchronization frame, and this 4. The communication method according to claim 3, wherein the time of the second counter is not synchronized when the difference from the time of the second counter when the time synchronization frame is received exceeds a predetermined value.   The local timer unit periodically indicates the time indicated by the first time stamp notified in the time synchronization frame after the start of communication by the user frame, and the time of the second counter when the time synchronization frame is received. 5. The communication method according to claim 4, wherein when the difference between the second counter and the second counter is equal to or less than the predetermined value, the time of the second counter is synchronized so as to reduce the difference stepwise.   A second subscriber-side communication device is arranged in parallel with a first subscriber-side communication device as a subscriber-side communication device to which the time synchronization unit is connected, and the station-side communication device is a first subscriber 4. The communication system according to claim 3, wherein the user frame is transferred via the second subscriber side communication device without going through the side communication device. Time stamp notification step of notifying a first time stamp, which is time information indicating the time of a first counter included in the station side communication device, in a time synchronization frame propagating from the station side communication device to the subscriber side communication device When,
RTT notification that propagates RTT (Round Trip Time), which is time information indicating the round-trip propagation time between the station-side communication device and the subscriber-side communication device, from the station-side communication device to the subscriber-side communication device An RTT notification step for notifying with a frame for use;
Based on the RTT notified in the RTT notification frame, the second time is time information indicating the time of the second counter synchronized with the time indicated by the first time stamp notified in the time synchronization frame. A time stamp correction step for correcting the stamp;
A communication method comprising:   A communication program for causing an electronic computer to execute the communication method according to claim 7.

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