PTP (Precision Time Protocol) and SDH (Synchronous Digital Hierarchy) cross-network time service method and device

Abstract

The invention relates to the technical field of time frequency transmission, in particular to a PTP and SDH cross-network time service method and device, an SDH overhead channel is used for transmitting a PTP time signal, compared with an E1 service channel, the overhead channel is fixed in position in an SDH frame structure, is not influenced by branch pointer adjustment and is small in transmission delay jitter, meanwhile, PTP messages are not directly transmitted, and the transmission efficiency is improved. The PTP protocol is converted into a simplified time service protocol and then is transmitted by using an SDH overhead channel, so that the bandwidth occupation is reduced, the time synchronization frequency can be improved, the time service precision is improved, in addition, a time signal transmission path is more flattened, a multi-layer communication protocol nesting and a communication protocol conversion buffer area required by directly transmitting the PTP protocol are avoided, and the transmission efficiency is improved. According to the invention, the transmission delay jitter is reduced, the time service precision is improved, and the technical problem that the time service precision is seriously degraded when the PTP time signal crosses the SDH network for long-distance transmission in the existing scheme is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of time-frequency transmission, and in particular to a PTP and SDH cross-network timing method and device. Background Art

[0002] Time and frequency transfer technology has important applications in the fields of communication, measurement and control, power systems, etc. Among them, PTP (Precision Time Protocol), also known as IEEE1588 protocol, is a network time synchronization protocol with sub-microsecond time synchronization performance and distributed networking capabilities. It has become a widely used industrial standard, but PTP is based on Ethernet technology and cannot directly perform high-precision time transfer in other communication networks. There is a problem that it cannot be interconnected with other time synchronization networks.

[0003] Prior art CN105119678A discloses a method for realizing PTP nanosecond precision transmission based on SDH_E1 network, by directly loading PTP message into the E1 service channel of SDH (Synchronous Digital Hierarchy) for transmission, adding a converter between PTP device and SDH device to realize communication protocol conversion, the method discloses a dynamic time deviation compensation method for transmitting PTP time signal through E1 channel of SDH network, realizing long-distance transmission of PTP time signal across SDH network.

[0004] However, the above solution only converts the underlying communication technology protocol, loads the PTP message into the SDH E1 service for transmission, and does not process the payload data (PTP message) to achieve transparent transmission of the PTP message. The transmission process based on the SDH service channel is relatively complex, including a series of processes such as low-order cross-connection, high-order channel, and framing. In addition, affected by the branch pointer adjustment, there is a large delay uncertainty in data transmission, which ultimately affects the timing accuracy of PTP. Therefore, although this solution realizes the cross-network timing of PTP, the timing accuracy is seriously degraded, which is a technical solution that sacrifices performance. Summary of the invention

[0005] The purpose of the present invention is to provide a PTP and SDH cross-network timing method and device, which solves the technical problem that when the PTP time signal in the existing solution crosses the SDH network for long-distance transmission, the SDH overhead channel bandwidth is limited and the multi-layer protocol nesting and communication protocol conversion buffer will increase the delay jitter, resulting in serious degradation of the timing accuracy.

[0006] To achieve the above object, the present invention provides a PTP and SDH cross-network timing method, comprising the following steps:

[0007] At the SDH master station, set the PTP clock unit to PTP slave clock mode and synchronize it to the external PTP master clock.

[0008] Then, the synchronization time frequency is sent to the timing protocol conversion unit through the three signals of TOD, PPS and CLK, and a new simplified timing protocol is regenerated;

[0009] Afterwards, the simplified timing protocol is inserted into the idle overhead byte of the SDH frame through the SDH overhead processing unit for long-distance transmission;

[0010] At the SDH slave station end, a series of reverse processes are implemented to recover the synchronous time and frequency signal from the SDH network by the timing protocol conversion unit by running the timing protocol;

[0011] Then, the synchronous time frequency is sent to the PTP clock unit through the TOD, PPS and CLK signals and reconverted into the standard PTP protocol;

[0012] Finally, the PTP clock unit is set to the master clock mode, and the external PTP slave clock is corrected to complete the entire timing process.

[0013] Wherein, the time synchronization implementation process between the timing protocol conversion unit and the internal PTP clock unit is:

[0014] At the SDH master station, the clock synthesis unit selects the clock signal output by the PTP clock unit as the reference clock, synthesizes the 155.52MHz clock required by the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same clock source;

[0015] The timing protocol conversion unit receives the TOD and PPS signals output by the PTP clock unit, and the internal TOD decoder extracts the time information from the TOD signal and sends it to the PPS timer. The PPS timer corrects the current time when the rising edge of the PPS signal arrives, and sends the corrected time and the PPS signal to the protocol framing module;

[0016] At the SDH slave station end, the clock synthesis unit selects the SDH line recovery clock as the reference clock, synthesizes the clocks required by the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same source of clocks;

[0017] The PPS timer inside the timing protocol conversion unit generates the PPS signal and time information through frequency counting, the TOD encoder converts the time information generated by the PPS timer into the TOD signal, and the PTP clock unit receives the PPS signal and the TOD signal output by the timing protocol conversion unit, and corrects the current time.

[0018] The time synchronization between the SDH master station and the SDH slave station is implemented as follows:

[0019] The timing protocol conversion unit adopts a simplified timing protocol to achieve time synchronization between the SDH master station and the SDH slave station. The SDH master station and the slave station complete transmission delay measurement and information transmission by exchanging timing protocol frames. The SDH slave station obtains a relatively accurate time compensation value through calculation and error processing. The time compensation value is used to correct the local clock to achieve synchronization with the SDH master station time.

[0020] The specific process of synchronizing the SDH master station and the SDH slave station is as follows:

[0021] The SDH slave station controls the protocol framing module to send a request frame at time t1, and triggers the time interval measurement module to start measurement;

[0022] When the protocol de-framing module of the SDH master station receives the REQ frame, it immediately triggers the time interval measurement module to start the measurement. At time t3, it controls the protocol framing module to send a response frame and stop the time interval measurement to obtain the time interval measurement value T. mm = t3-t2;

[0023] When the protocol de-framing module of the SDH slave station receives the ACK frame, it stops the time interval measurement and obtains the time interval measurement value T ss = t4-t1;

[0024] When the PPS signal is generated, the SDH master station immediately triggers the time interval measurement module to start measurement, and at time t6, the control protocol framing module sends a signal containing the time measurement value T mm The pulse signal frame is set and the time interval measurement is stopped to obtain the time interval measurement value T pps =t6-t5;

[0025] When the protocol de-framing module of the SDH slave station receives the PS frame, it parses it to obtain the time measurement value T mm ;

[0026] At time t8, the SDH master station controls the protocol framing module to send a message containing the time measurement value T pps and a time signal frame containing UTC time information;

[0027] When the protocol de-framing module of the SDH slave station receives the TS frame, it parses it to obtain the time measurement value T pps and UTC time information.

[0028] Among them, when the SDH master station and the slave station send the protocol frame, in order to obtain deterministic transmission delay and reduce jitter, the frame data should be written into the sender FIFO buffer when the SDH frame header signal TTOHFP is detected. After the above series of processes, the SDH slave station clock servo module can obtain T mm , T ss , T pps_m The three time interval measurement values ​​and the UTC time of the SDH master station, assuming that the bidirectional path is symmetrical, can be used to calculate the transmission path delay T from the SDH master station to the slave station. m2s =(T ss -T mm ) / 2, PPS transmission delay T pps_ms =T m2s +T pps_m The clock servo module is used to obtain UTC time information and PPS transmission delay value T pps_ms Correcting the local PPS timer can achieve time synchronization with the SDH master station, and path asymmetry can be compensated by external technical means.

[0029] The present invention also provides a PTP and SDH cross-network timing device, comprising a clock synthesis unit, a PTP clock unit, a timing protocol conversion unit and an SDH overhead processing unit, wherein the clock synthesis unit is connected to the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit respectively, and the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit are connected in sequence;

[0030] The clock synthesis unit is used to realize the clock homology of the whole system;

[0031] The PTP clock unit is used to synchronize time with an external PTP clock device;

[0032] The timing protocol conversion unit is used to achieve time synchronization with the internal PTP clock unit, and long-distance time synchronization between the SDH master station and the SDH slave station;

[0033] The SDH overhead processing unit is used to insert and extract the SDH overhead, insert the timing protocol information into the idle overhead bytes of the SDH frame at the line sending end, and extract the timing protocol information from the overhead bytes corresponding to the SDH frame at the line receiving end.

[0034] The invention discloses a PTP and SDH cross-network timing method and device. The PTP time signal is transmitted by using an SDH overhead channel. Compared with an E1 service channel, the overhead channel has a fixed position in the SDH frame structure and is not affected by the branch pointer adjustment. The transmission delay jitter is small. Meanwhile, the PTP message is not directly transmitted, but the PTP protocol is converted into a simplified timing protocol and then transmitted using the SDH overhead channel, thereby reducing bandwidth occupancy, improving the time synchronization frequency, and improving the timing accuracy. In addition, the time signal transmission path is flatter, and the multi-layer communication protocol nesting and communication protocol conversion buffer required for the direct transmission of the PTP protocol are avoided, thereby reducing the transmission delay jitter and improving the timing accuracy. The invention solves the technical problem in the existing solution that when the PTP time signal crosses the SDH network for long-distance transmission, the limited bandwidth of the SDH overhead channel and the multi-layer protocol nesting and communication protocol conversion buffer will increase the delay jitter, thereby causing the timing accuracy to be seriously deteriorated. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0036] Figure 1 It is a flowchart of the PTP and SDH cross-network timing method according to the first embodiment of the present invention.

[0037] Figure 2 It is a flow chart of the steps of implementing time synchronization between a timing protocol conversion unit and an internal PTP clock unit in a PTP and SDH cross-network timing method according to a first embodiment of the present invention.

[0038] Figure 3 It is a flowchart of the timing of the SDH master station and the SDH slave station in the PTP and SDH cross-network timing method of the first embodiment of the present invention.

[0039] Figure 4 It is a specific flow chart of the synchronization between the SDH master station and the SDH slave station according to the first embodiment of the present invention.

[0040] Figure 5 It is a schematic diagram of the overall structure of the PTP and SDH cross-network timing device of the second embodiment of the present invention.

[0041] Figure 6 It is a schematic diagram of signal transmission between a PTP and SDH inter-network timing device and an external Ethernet according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0043] First embodiment:

[0044] See also Figures 1 to 4 The present invention provides a PTP and SDH cross-network timing method, comprising the following steps:

[0045] S101, at the SDH master station, set the PTP clock unit to PTP slave clock mode and synchronously track the external PTP master clock;

[0046] S102, then, the synchronization time frequency is sent to the timing protocol conversion unit through the three signals of TOD (Time Of Day, a serial time interface protocol), PPS (Pulse Per Second), and CLK (Clock), and a new simplified timing protocol is regenerated;

[0047] S103, then, inserting the simplified timing protocol into the idle overhead byte of the SDH frame through the SDH overhead processing unit for long-distance transmission;

[0048] S104, at the SDH slave station end, implement a series of reverse processes, and restore the synchronous time and frequency signal from the SDH network by the timing protocol conversion unit by running the timing protocol;

[0049] S105, sending the synchronized time frequency to the PTP clock unit through the TOD, PPS and CLK signals and reconverting them into the standard PTP protocol;

[0050] S106. Finally, the PTP clock unit is set to the master clock mode, and the external PTP slave clock is calibrated to complete the entire timing process.

[0051] Specifically, the time synchronization implementation process between the timing protocol conversion unit and the internal PTP clock unit is:

[0052] S107, at the SDH master station end, the clock synthesis unit selects the clock signal (CLK) output by the PTP clock unit as the reference clock, synthesizes the 155.52 MHz clock required by the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same clock source;

[0053] S108, the timing protocol conversion unit receives the TOD and PPS signals output by the PTP clock unit, and the internal TOD decoder extracts the time information from the TOD signal and sends it to the PPS timer, and the PPS timer corrects the current time when the rising edge of the PPS signal arrives, and sends the corrected time and the PPS signal to the protocol framing module;

[0054] S109, at the SDH slave station end, the clock synthesis unit selects the SDH line recovery clock as the reference clock, synthesizes the clocks required by the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same source of clocks;

[0055] S110, the PPS timer inside the timing protocol conversion unit generates the PPS signal and time information through frequency counting, the TOD encoder converts the time information generated by the PPS timer into the TOD signal, the PTP clock unit receives the PPS signal and the TOD signal output by the timing protocol conversion unit, and corrects the current time.

[0056] The time synchronization between the SDH master station and the SDH slave station is implemented as follows:

[0057] The timing protocol conversion unit adopts a simplified timing protocol to achieve time synchronization between the SDH master station and the SDH slave station. The SDH master station and the slave station complete transmission delay measurement and information transmission by exchanging timing protocol frames. The SDH slave station obtains a relatively accurate time compensation value through calculation and error processing. The time compensation value is used to correct the local clock to achieve synchronization with the SDH master station time.

[0058] Specifically, the specific process of synchronizing the SDH master station and the SDH slave station is as follows:

[0059] S111, the SDH slave station controls the protocol framing module to send a request frame (REQ frame) at time t1, and triggers the time interval measurement module to start measurement;

[0060] S112: When the protocol deframing module of the SDH master station receives the REQ frame (at time t2), it immediately triggers the time interval measurement module to start measurement. At time t3, it controls the protocol framing module to send a response frame (ACK frame) and stop the time interval measurement to obtain the time interval measurement value T. mm = t3-t2;

[0061] S113, when the protocol de-framing module of the SDH slave station receives the ACK frame (time t4), the time interval measurement is stopped to obtain the time interval measurement value T ss = t4-t1;

[0062] S114, when the PPS signal is generated (at time t5), the SDH master station immediately triggers the time interval measurement module to start measurement, and at time t6 controls the protocol framing module to send a signal containing the time measurement value T mm The pulse signal frame (PS frame) is taken and the time interval measurement is stopped to obtain the time interval measurement value T pps =t6-t5;

[0063] S115, when the protocol de-framing module of the SDH slave station receives the PS frame (at time t7), it parses and obtains the time measurement value T mm ;

[0064] S116, the SDH master station controls the protocol framing module to send a message containing the time measurement value T at time t8. pps and time signal frame (TS frame) containing UTC time information;

[0065] S117, when the protocol de-framing module of the SDH slave station receives the TS frame (at time t9), it parses and obtains the time measurement value T pps and UTC time information.

[0066] Among them, when the SDH master station and the slave station send the protocol frame, in order to obtain deterministic transmission delay and reduce jitter, the frame data should be written into the sender FIFO buffer when the SDH frame header signal TTOHFP is detected. After the above series of processes, the SDH slave station clock servo module can obtain T mm 、T ss 、T pps_m The three time interval measurement values ​​and the UTC time of the SDH master station, assuming that the bidirectional path is symmetrical, can be used to calculate the transmission path delay T from the SDH master station to the slave station. m2s =(T ss -T mm ) / 2, PPS transmission delay T pps_ms =T m2s +T pps_m The clock servo module is used to obtain UTC time information and PPS transmission delay value T pps_ms Correcting the local PPS timer can achieve time synchronization with the SDH master station, and path asymmetry can be compensated by external technical means.

[0067] When using a PTP and SDH cross-network timing method of the present embodiment, the PTP time signal is transmitted by using the SDH overhead channel. Compared with the E1 service channel, the overhead channel has a fixed position in the SDH frame structure and is not affected by the branch pointer adjustment. The transmission delay jitter is small. At the same time, the PTP message is not directly transmitted, but the PTP protocol is converted into a streamlined timing protocol and then transmitted using the SDH overhead channel, which reduces bandwidth occupancy, can increase the timing frequency, and improve the timing accuracy. In addition, the time signal transmission path is flatter, avoiding the multi-layer communication protocol nesting and communication protocol conversion buffer required for direct transmission of the PTP protocol, reducing transmission delay jitter, and improving timing accuracy. The technical problem that the timing accuracy is seriously deteriorated due to the limited bandwidth of the SDH overhead channel and the multi-layer protocol nesting and communication protocol conversion buffer when the PTP time signal in the existing solution is transmitted across the SDH network for a long distance is solved.

[0068] Second embodiment:

[0069] Based on the first embodiment, please refer to Figure 5 and Figure 6 The present invention also provides a PTP and SDH cross-network timing device, including a clock synthesis unit, a PTP clock unit, a timing protocol conversion unit and an SDH overhead processing unit.

[0070] In this embodiment, the PTP and SDH cross-network timing device does not directly transmit PTP messages. A cross-network timing device is added between the PTP and SDH networks to realize timing protocol conversion and SDH overhead insertion and extraction. Through the coordinated use of the clock integration unit, the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit, the bandwidth occupancy can be reduced, the timing frequency can be increased, and the time signal transmission path can be flatter, thereby reducing delay jitter and improving timing accuracy.

[0071] Wherein, the clock synthesis unit is connected to the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit respectively, and the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit are connected in sequence;

[0072] The clock synthesis unit is used to realize the clock homology of the whole system;

[0073] The PTP clock unit is used to synchronize time with an external PTP clock device;

[0074] The timing protocol conversion unit is used to achieve time synchronization with the internal PTP clock unit, and long-distance time synchronization between the SDH master station and the SDH slave station;

[0075] The SDH overhead processing unit is used to insert and extract the SDH overhead.

[0076] Secondly, the clock synthesis unit selects the clock signal output by the PTP clock unit as the reference clock source at the SDH master station end, and selects the clock recovered from the SDH line as the reference clock source at the SDH slave station end, so as to realize the clock homology of the whole system.

[0077] Again, the PTP clock unit is set to slave clock mode at the SDH master station end to achieve time synchronization with the external PTP master clock device, and is set to master clock mode at the SDH slave station end to provide a time reference for the external PTP slave clock device, thereby finally achieving time synchronization with the external PTP clock device.

[0078] In addition, the SDH overhead processing unit inserts the timing protocol information into the idle overhead bytes of the SDH frame at the line sending end, and extracts the timing protocol information from the overhead bytes corresponding to the SDH frame at the line receiving end, thereby realizing the insertion and extraction of the SDH overhead.

[0079] Finally, the main functional modules of the timing protocol conversion unit are all implemented using FPGA, including TOD encoder / decoder, PPS timer, protocol framing module, protocol deframing module, time interval measurement module, clock servo module and FIFO buffer.

[0080] When a PTP and SDH inter-network timing device of this embodiment is used, the PTP and SDH inter-network timing device is mainly composed of the clock synthesis unit, the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit. Among them, the clock synthesis unit, the PTP clock unit and the SDH overhead processing unit are mature basic technologies, and there are no special requirements for internal implementation details. The design focuses on the timing protocol conversion unit and the interconnection and coordination between the units.

[0081] The clock synthesis unit is used to realize the same source of the clock of the entire system. At the SDH master station end, the clock signal (CLK) output by the PTP clock unit is selected as the reference clock source. At the SDH slave station end, the clock recovered from the SDH line is selected as the reference clock source to synthesize the 155.52MHz clock required by the timing protocol conversion unit and the SDH overhead processing unit.

[0082] The PTP clock unit is responsible for synchronizing with the external PTP clock device. At the SDH master station end, it is set to the slave clock mode to achieve time synchronization with the external PTP master clock device. At the SDH slave station end, it is set to the master clock mode to provide a time reference for the external PTP slave clock device.

[0083] The SDH overhead processing unit is used to insert and extract the SDH overhead, insert the timing protocol information into the idle overhead bytes of the SDH frame at the line sending end, and extract the timing protocol information from the overhead bytes corresponding to the SDH frame at the line receiving end.

[0084] The timing protocol conversion unit realizes time synchronization with an internal PTP clock unit on the one hand, and realizes long-distance time synchronization between an SDH master station and an SDH slave station on the other hand. The main functional modules are all implemented using FPGA, including a TOD encoder / decoder, a PPS timer, a protocol framing module, a protocol deframing module, a time interval measurement module, a clock servo module, and a FIFO (First In First Out) buffer, etc.

[0085] During the time synchronization between the SDH master station and the SDH slave station, in order to obtain deterministic transmission delay and reduce jitter when the SDH master station and the slave station send protocol frames, the frame data should be written into the sender FIFO buffer when the SDH frame header signal TTOHFP is detected.

[0086] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A PTP and SDH inter-network timing method, characterized in that: The following steps are involved: At the SDH master station, set the PTP clock unit to PTP slave clock mode and synchronize it to the external PTP master clock. Then, the synchronization time frequency is sent to the timing protocol conversion unit through the three signals of TOD, PPS and CLK, and a new simplified timing protocol is regenerated; Afterwards, the simplified timing protocol is inserted into the idle overhead byte of the SDH frame through the SDH overhead processing unit for long-distance transmission; At the SDH slave station end, a series of reverse processes are implemented to recover the synchronous time and frequency signal from the SDH network by the timing protocol conversion unit by running the timing protocol; Then, the synchronous time frequency is sent to the PTP clock unit through the TOD, PPS and CLK signals and reconverted into the standard PTP protocol; Finally, the PTP clock unit is set to the master clock mode, and the external PTP slave clock is corrected to complete the entire timing process.

2. The PTP and SDH inter-network timing method according to claim 1, wherein: The time synchronization implementation process between the timing protocol conversion unit and the internal PTP clock unit is: At the SDH master station, the clock synthesis unit selects the clock signal output by the PTP clock unit as the reference clock, synthesizes the 155.52MHz clock required by the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same clock source; The timing protocol conversion unit receives the TOD and PPS signals output by the PTP clock unit, and the internal TOD decoder extracts the time information from the TOD signal and sends it to the PPS timer. The PPS timer corrects the current time when the rising edge of the PPS signal arrives, and sends the corrected time and the PPS signal to the protocol framing module; At the SDH slave station end, the clock synthesis unit selects the SDH line recovery clock as the reference clock, synthesizes the clocks required by the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit, and realizes the same source of clocks; The PPS timer inside the timing protocol conversion unit generates the PPS signal and time information through frequency counting, the TOD encoder converts the time information generated by the PPS timer into the TOD signal, and the PTP clock unit receives the PPS signal and the TOD signal output by the timing protocol conversion unit, and corrects the current time.

3. The PTP and SDH inter-network timing method as claimed in claim 1, characterized in that: The time synchronization between the SDH master station and the SDH slave station is implemented as follows: The timing protocol conversion unit adopts a simplified timing protocol to achieve time synchronization between the SDH master station and the SDH slave station. The SDH master station and the slave station complete transmission delay measurement and information transmission by exchanging timing protocol frames. The SDH slave station obtains a relatively accurate time compensation value through calculation and error processing. The time compensation value is used to correct the local clock to achieve synchronization with the SDH master station time.

4. The PTP and SDH inter-network timing method as claimed in claim 3, characterized in that: The specific process of synchronizing the SDH master station and the SDH slave station is as follows: The SDH slave station controls the protocol framing module to send a request frame at time t1, and triggers the time interval measurement module to start measurement; When the protocol de-framing module of the SDH master station receives the REQ frame, it immediately triggers the time interval measurement module to start the measurement. At time t3, it controls the protocol framing module to send a response frame and stop the time interval measurement to obtain the time interval measurement value T. mm = t3-t2; When the protocol de-framing module of the SDH slave station receives the ACK frame, it stops the time interval measurement and obtains the time interval measurement value T ss =t4-t1; When the PPS signal is generated, the SDH master station immediately triggers the time interval measurement module to start measurement. At time t6, the control protocol framing module sends a pulse signal frame containing the time measurement value Tmm and stops the time interval measurement, obtaining the time interval measurement value T pps =t6-t5; When the protocol de-framing module of the SDH slave station receives the PS frame, it parses it to obtain the time measurement value T mm ; At time t8, the SDH master station controls the protocol framing module to send a message containing the time measurement value T pps and a time signal frame containing UTC time information; When the protocol de-framing module of the SDH slave station receives the TS frame, it parses it to obtain the time measurement value T pps and UTC time information.

5. The PTP and SDH inter-network timing method as claimed in claim 4, characterized in that: When the SDH master station and slave station send protocol frames, in order to obtain deterministic transmission delay and reduce jitter, the frame data should be written into the sender FIFO buffer when the SDH frame header signal TTOHFP is detected. After the above series of processes, the SDH slave station clock servo module can obtain T mm , T ss , T pps_m The three time interval measurement values ​​and the UTC time of the SDH master station, assuming that the bidirectional path is symmetrical, can be used to calculate the transmission path delay T from the SDH master station to the slave station. m2s =(T ss -T mm ) / 2, PPS transmission delay T pps_ms =T m2s +T pps_m The clock servo module is used to obtain UTC time information and PPS transmission delay value T pps_ms Correcting the local PPS timer can achieve time synchronization with the SDH master station, and path asymmetry can be compensated by external technical means.

6. A PTP and SDH inter-network timing device, applied to the PTP and SDH inter-network timing method according to any one of claims 1 to 5, characterized in that: It comprises a clock synthesis unit, a PTP clock unit, a timing protocol conversion unit and an SDH overhead processing unit, wherein the clock synthesis unit is connected to the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit respectively, and the PTP clock unit, the timing protocol conversion unit and the SDH overhead processing unit are connected in sequence; The clock synthesis unit is used to realize the clock homology of the whole system; The PTP clock unit is used to synchronize time with an external PTP clock device; The timing protocol conversion unit is used to achieve time synchronization with the internal PTP clock unit, and long-distance time synchronization between the SDH master station and the SDH slave station; The SDH overhead processing unit is used to insert and extract the SDH overhead, insert the timing protocol information into the idle overhead bytes of the SDH frame at the line sending end, and extract the timing protocol information from the overhead bytes corresponding to the SDH frame at the line receiving end.

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