WO2021004005A1

WO2021004005A1 - Timestamp jitter compensation method and system

Info

Publication number: WO2021004005A1
Application number: PCT/CN2019/124990
Authority: WO
Inventors: 陈驰; 吴倩
Original assignee: 烽火通信科技股份有限公司; 武汉飞思灵微电子技术有限公司
Priority date: 2019-07-10
Filing date: 2019-12-13
Publication date: 2021-01-14
Also published as: CN112217588A; CN112217588B

Abstract

The present invention relates to the field of time synchronization, and disclosed are a timestamp jitter compensation method and system. The method is applicable to a packet that has a timestamp. The method comprises the step of: a receiving end compensates for the timestamp of a current packet according to a sending time interval between the current packet and a previous packet and a receiving time interval between the current packet and the previous packet. In the present invention, the timestamp of the current packet is compensated and corrected by means of the sending time interval and the receiving time interval of two adjacent packets. That is, delay jitter and time synchronization jitter are prevented by means of the sending time interval and receiving time interval, which not only significantly improves clock synchronization accuracy and effectively reduces the impact of link delay jitter on synchronization stability, but also does not need to take into consideration the location and clock frequency of a timestamp record, i.e. hardware does not need to be improved.

Description

Time stamp jitter compensation method and system

Technical field

The invention relates to the field of time synchronization, in particular to a time stamp jitter compensation method and system.

Background technique

The PTP protocol (Precision Time Protocol) or the 1588 protocol provides a mechanism for time synchronization in Ethernet. It uses the symmetry and delay measurement of the network to achieve master control between nodes. The synchronization of the slave time allows the slave device and the master device to have a consistent clock frequency and phase.

As shown in Figure 1, the existing time synchronization method is: assuming that the link delay between the master and slave stations is symmetric, that is, the link delay between the master station and the slave station Tms = the link from the station to the master station Time delay Tsm.

The slave clock of the slave station can calculate the time offset and link delay between it and the master clock of the master station according to the four time stamps t1, t2, t3, and t4 obtained, namely:

Time offset Offset=[(t2-t1)-(t4-t3)]/2

Link delay Delay=[(t2-t1)+(t4-t3)]/2.

With the rapid development of the mobile Internet, the demand for various new applications such as the Internet of Things and the Internet of Vehicles has soared, the explosive growth of data traffic and the massive amount of access devices, the fifth generation of mobile communications (5G) technology has emerged. 5G technology puts forward higher requirements for the accuracy of time synchronization in the bearer network. Furthermore, the ultimate performance of time synchronization is highly sensitive to link delay jitter, requiring more accurate recording of message timestamps, that is, the location is closer to the actual physical port, and the processing clock frequency of message timestamps is further improved.

At present, because the location of the time stamp record cannot be located on the physical link port, the message will go through a series of operations such as non-fixed buffering or AM codeword insertion and deletion from the time stamping to the physical link port. There is jitter in the link delay (see Figure 2), which leads to jitter in time synchronization.

In order to solve the above problems, people in the industry have thought of the following two ways:

1. The location of the time stamp record is located at the physical link port;

2. Increase the clock frequency of the sender and receiver, thereby reducing the jitter range of time synchronization.

However, the above two methods are difficult to implement due to hardware limitations; after testing, the existing time synchronization method can only achieve the time error between the sender and the receiver within ±200ns, which does not meet the time synchronization requirements of 5G technology (error within ±5ns) Within)

Summary of the invention

In view of the defects in the prior art, the technical problem solved by the present invention is: how to improve the time synchronization accuracy without improving the hardware.

In order to achieve the above objectives, the present invention provides a time stamp jitter compensation method, which is suitable for messages with time stamps. The method includes the following steps: the receiving end according to the sending time interval between this message and the last message, And the time interval between the current message and the last message received, to compensate the timestamp of the current message.

Based on the above technical solution, the specific steps of the method include: the sending end sends the sending time interval to the receiving end along with this message; the receiving end subtracts the sending time interval from the receiving time interval to obtain the sending and receiving time interval If the difference Δt is normal, the receiving end adds the receiving timestamp of the current message to the receiving and sending Δt to obtain the compensated receiving timestamp, and marks the timestamp as the receiving timestamp of the current message.

On the basis of the above technical solution, the method for judging that the transmission and reception time interval difference Δt is normal is to determine whether the absolute value of the transmission and reception time interval difference Δt is greater than the preset value of link delay jitter; if so, determine the transmission and reception time interval difference If Δt is abnormal, otherwise, it is determined that the difference Δt between the transmission and reception time intervals is normal; the preset value of the link delay jitter is at least greater than the maximum value of the transmission and reception time interval difference.

Based on the above technical solution, the packet is a PTP packet, the transmitting end transmits the packet with the current time last _sent packet interval t, with the flow receiving end of the packet sent to this include: The sender replaces the reserved field in the PTP message with t _sent .

On the basis of the above technical solution, the prerequisite for implementing the method is that the clock frequency of the sending end and the receiving end are synchronized.

The time stamp jitter compensation system provided by the present invention is suitable for messages with time stamps. The system includes a time stamp compensation module arranged on the receiving end, which is used for: according to the current message and the last message Compensate the time stamp of the current message with the sending time interval of the current message and the time interval of receiving the last message.

Based on the above technical solution, the system further comprises at the transmitting end of the transmission time interval of a transmission module configured to: _send a transmission time interval t with the current packet to the receiving end; the time stamp compensation module work The process includes: after receiving the message, the receiving end calculates the receiving time interval t _receive , and calculates the sending and receiving time interval difference Δt based on t _sending and t _receiving . The calculation formula is: Δt=t _sending- t _receiving ; if Δt is normal, then Add Δt to the receiving timestamp of this message to obtain the compensated receiving timestamp, and mark this timestamp as the receiving timestamp of this message.

On the basis of the above technical solution, the method for the time stamp compensation module to determine whether the transmission and reception time interval difference Δt is normal is to determine whether the absolute value of the transmission and reception time interval difference Δt is greater than the preset value of link delay jitter; If yes, it is determined that the transmission and reception time interval difference Δt is abnormal; otherwise, it is determined that the transmission and reception time interval difference Δt is normal.

Based on the above technical solution, the packet is a PTP packet, the transmission time interval to the transmission module of this packet transmission time interval t last packet _sent, with this packet to the receiving end The process includes: replacing the reserved field in the PTP message with t _sending .

On the basis of the above technical solution, the system also includes local time counters respectively arranged at the sending end and the receiving end and synchronized with the clock frequency, which are used to record the time stamp of sending or receiving messages.

Compared with the prior art, the advantages of the present invention are:

The present invention compensates and corrects the time stamp of this message through the sending time interval and receiving time interval of two adjacent messages; that is, the time delay jitter and the time synchronization jitter are avoided by the sending time interval and the receiving time interval, It not only significantly improves the clock synchronization accuracy, but also effectively reduces the impact of link delay jitter on synchronization stability; and there is no need to consider the location of the time stamp recording and the clock frequency, that is, no hardware improvement is required.

It is obtained through testing that the error between the time stamp of the receiving end and the time stamp corresponding to the transmitting end after compensation by the present invention is within ±5ns.

At the same time, the above method is not only different from the prior art, but it is also very difficult for those of ordinary skill in the art to think of the above method. The reason is that as mentioned in the background art, the conventional improvement concept is: Physical link ports, or increase the clock frequency of the sender and receiver, thereby reducing the jitter range of time synchronization. In addition, there is no document that discloses or mentions the specific realization or idea of the above-mentioned method.

Description of the drawings

Figure 1 is a schematic diagram of the principle of time synchronization in the background art;

Figure 2 is a schematic diagram of a time synchronization implementation model in the background art;

FIG. 3 is a schematic flowchart of a time stamp jitter compensation method in an embodiment of the present invention;

4 is a schematic diagram of the description of the fields of the PTP message common header in the 1588v2 protocol defined by ITU-T in the embodiment of the present invention;

Figure 5 is a schematic diagram of a time synchronization implementation model in an embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the drawings and embodiments.

The time stamp jitter compensation method in the embodiment of the present invention is suitable for messages with time stamps, and the method includes the following steps:

The receiving end compensates for the time stamp of the current message according to the time interval between the current message and the last message and the time interval between the current message and the last message.

It can be seen from this that the present invention compensates and corrects the time stamp of this message through the transmission time interval and the reception time interval of the two adjacent messages; that is, the transmission time interval and the reception time interval are used to avoid delay jitter and delay. Time synchronization jitter not only significantly improves the clock synchronization accuracy, but also effectively reduces the impact of link delay jitter on synchronization stability; it does not need to consider the location of the time stamp recording and the clock frequency, that is, there is no need to improve the hardware.

Preferably, the step of compensating the time stamp of the current message according to the sending time interval between the current message and the last message and the receiving time interval between the current message and the last message includes:

The transmitting side transmits this packet to the time the last packet _sent interval t, with this message to the receiving end;

After receiving this message, the receiving end calculates the receiving time interval between this message and the last message t _receive , and calculates the difference Δt between the _sending and receiving time according to t _sending and t _receiving , the calculation formula is: Δt = t _sending- t _Receive

If the difference between the sending and receiving time interval Δt is normal, the receiving end adds the receiving time stamp of the current message to the sending and receiving time interval difference Δt to obtain the compensated receiving time stamp, and mark the time stamp as the receiving time of the current message stamp.

Preferably, the packet is a PTP packet, the transmitting end transmits the packet with the current time last _sent packet interval t, with this packet to the receiving end the process comprising: the transmitting side in the PTP message the reserved field is replaced with t _hair, so basically the design of the software will not change, and the rational use of resources.

Preferably, the method for judging that the transmission and reception time interval difference Δt is normal is: judging whether the absolute value of the transmission and reception time interval difference Δt is greater than the preset value of link delay jitter; if so, it is determined that the transmission and reception time interval difference Δt is abnormal , Otherwise it is determined that the transmission and reception time interval difference Δt is normal. The principle of this design is to effectively avoid the error time data caused by other abnormal reasons such as software or hardware. If the interval difference Δt is 500ns, it is obvious that the time data this time is the wrong data obtained due to abnormal reasons (such as data packet loss, etc.), and subsequent compensation with this data will only make mistakes.

In practical applications, the preset value of link delay jitter is set according to specific scenarios and experience;

Setting according to specific scenarios means: In order to effectively avoid the wrong time data caused by other abnormal reasons such as software or hardware, the preset value of link delay jitter should be at least greater than the maximum value of the difference between the transmission and reception time, and the transmission time interval is poor The maximum value is determined according to different scenarios;

Setting based on experience refers to determining based on experience how much the preset value of link delay jitter is greater than the maximum value of the difference between the transmission and reception time intervals, generally about 10ns.

Preferably, the frequency of the local time counter that records the time stamp on the sending end and the receiving end is synchronized. In this embodiment, both are 32 bits. The advantage of such a design is that the sending interval of a typical PTP message is usually less than 1 second/time, and the local time The 32-bit counter can count from 0 to 4.3s, which satisfies typical application scenarios; a continuous 32-bit reserved field is defined in the common header of the PTP message, which can just pass a 32-bit counter.

In order to facilitate a comprehensive understanding, referring to Fig. 3, the method of the present invention will be described through a complete embodiment below.

S1: The receiving end and the sending end synchronize the clock frequency through SyncE, and a 32-bit local real-time time counter is maintained at the receiving end and the sending end.

S2: The sender records the 32-bit local real-time time corresponding to each message sent. When sending the message, it obtains the 32-bit local real-time time interval between the current message and the previous message (there is no previous message when the message is sent for the first time). A message, so the time interval is 0), that is, the sending time interval t is _sent .

S3: the transmission side while transmitting the current packet, the packet is replaced with a reserved field for a transmission time interval t 32bit _hair; packets embodiment according to the present embodiment is a PTP message, see FIG. 4, the present embodiment redefined 32bit reserved field (Offset = 16) packets, this field for transmitting the transmission time interval t _hair.

S4: The receiving end compares the receiving real-time time of the current received message with the previous received message to obtain the receiving time interval t _received .

S5: Remove the receiving end corresponding to the packet transmission time from the PTP message reserved field _hair interval t, with t t _yield obtained by subtracting the _hair transceiver difference interval Δt.

S6: The receiving end judges whether the absolute value of the difference Δt between the sending and receiving time interval is greater than the preset value of the link delay jitter, if it is, it means that the time data is wrong, and the difference is treated as 0 and ends; otherwise, the difference between the sending and receiving time interval Δt is obtained and transferred To S7.

S7: The receiving end adds the receiving timestamp of the current message to the difference Δt of the sending and receiving time to obtain the compensated receiving timestamp, and marks the timestamp as the receiving timestamp of the current message.

As shown in Fig. 5, the two upward solid arrows on the right side of Fig. 5 represent the receiving time interval t _received without using the method of the present invention. It can be seen that the jitter of the link delay results in the receiving time of the message at the receiving end. packet interval is not equal to the transmitting side transmission time interval; the right side in the broken line arrow in FIG. 5 up to the solid line arrows represent the present invention up to the time stamp corrected _received after reception time interval t, it can be seen reception time interval after the correction The time interval between t _receiving and sending t _is equal.

The time stamp jitter compensation system in the embodiment of the present invention includes a time stamp compensation module arranged on the receiving end, which is used for: according to the sending time interval of this message and the last message, and the current message and the previous message. The time interval for receiving the second message compensates for the time stamp of the current message.

The system further includes a transmission time interval of the transmission side disposed in transmission module configured to: send the packet and the current time last _sent packet interval t, with this message to the receiving terminal; the time stamp compensation workflow module comprising: the receiver receives the packet, this packet is calculated with the last reception time t _received packet interval t according to the calculated transceiver _send and _receive time interval t difference [Delta] t, is calculated as follows: Δt = t _send- t _receive ; if the difference between the sending and receiving time interval Δt is normal, add the receiving timestamp of this message to the sending and receiving time interval difference Δt to obtain the compensated receiving timestamp, and mark the timestamp as the current report The timestamp of the receipt of the document.

The method for the time-stamp compensation module to determine whether the difference Δt between the transmission and reception time intervals is normal is to determine whether the absolute value of the difference between the transmission and reception time intervals Δt is greater than the preset value of the link delay jitter; if so, determine the difference between the transmission and reception time intervals Δt is abnormal, otherwise it is determined that the time difference Δt between sending and receiving is normal.

The transmission time interval module transmits the transmission packet with the current time last _sent packet interval t, with this packet to the receiving end the process comprising: replacing the message field reserved t _hair.

The system also includes 32-bit local time counters respectively set on the sending end and the receiving end, which are used to record the time stamp of sending or receiving messages.

It should be noted that when the system provided by the embodiment of the present invention performs inter-module communication, only the division of the above-mentioned functional modules is used as an example for illustration. In actual applications, the above-mentioned functions can be allocated by different functional modules as required. That is, the internal structure of the system is divided into different functional modules to complete all or part of the functions described above.

Further, the present invention is not limited to the above-mentioned embodiments. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the present invention. Within the scope of protection. The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims

A time stamp jitter compensation method, which is suitable for messages with time stamps, is characterized in that the method includes the following steps: the receiving end according to the sending time interval of this message and the last message, and this time The time interval between the message and the last message received is compensated for the time stamp of this message.
The time stamp jitter compensation method according to claim 1, wherein the specific steps of the method include: the sending end sends the sending time interval to the receiving end along with this message; the receiving end subtracts the sending time interval The receiving time interval obtains the sending and receiving time interval difference Δt. If the Δt is normal, the receiving end adds the receiving timestamp of the current message to the receiving and sending Δt to obtain the compensated receiving timestamp, and mark the timestamp as the current time The timestamp of the message received.
3. The time stamp jitter compensation method according to claim 2, wherein the method for judging that the transmission and reception time interval difference Δt is normal is to determine whether the absolute value of the transmission and reception time interval difference Δt is greater than the preset value of link delay jitter If yes, it is determined that the sending and receiving time interval difference Δt is abnormal, otherwise it is determined that the sending and receiving time interval difference Δt is normal; the preset value of the link delay jitter is at least greater than the maximum value of the sending and receiving time interval difference.
Timestamp shake compensation method according to claim 2, wherein: the packet is a PTP packet, the transmitting end transmits the packet with the current time last sent packet interval t, with this The process of sending the message to the receiving end includes: the sending end replaces the reserved field in the PTP message with t sending .
The time stamp jitter compensation method according to any one of claims 1 to 4, wherein the premise of implementing the method is that the clock frequency of the sending end and the receiving end are synchronized.
A time stamp jitter compensation system, which is suitable for messages with time stamps, is characterized in that: the system includes a time stamp compensation module arranged on the receiving end, which is used for: according to the current message and the last time The time interval between sending messages and the time between receiving this message and the last message are compensated for the time stamp of this message.
Stamp shake compensation system according to claim 6, wherein: the system further comprises a transmission time interval of the transmission side disposed in transmission module configured to: send a transmission time interval t with the current packet to the receiving end The working process of the time stamp compensation module includes: after receiving the message, the receiving end calculates the receiving time interval t received , and calculates the difference Δt of the sending and receiving time interval according to t sending and t receiving , the calculation formula is: Δt=t sending -t received ; if Δt is normal, add Δt to the receiving timestamp of the current message to obtain the compensated receiving timestamp, and mark the timestamp as the receiving timestamp of the current message.
The time stamp jitter compensation system according to claim 6, wherein the method for the time stamp compensation module to determine whether the transmission and reception time interval difference Δt is normal is to determine whether the absolute value of the transmission and reception time interval difference Δt difference value is greater than The link delay jitter preset value; if it is, it is determined that the transmission and reception time interval difference Δt is abnormal, otherwise, it is determined that the transmission and reception time interval difference Δt is normal.
Stamp shake compensation system according to claim 6, wherein: the packet is a PTP packet, the transmission time interval module transmits the transmission packet with the current time of the last sent packet interval t, The process of sending this message to the receiving end includes: replacing the reserved field in the PTP message with t sending .
The time stamp jitter compensation system according to any one of claims 6 to 9, characterized in that: the system further comprises a local time counter which is respectively set at the sending end and the receiving end and synchronized with the clock frequency, which is used to record and send Or the timestamp of the received message.