Method for delay monitoring

Abstract

The invention relates to a method for transmitting data between two endpoints A, B, which particularly requires a common time of day at the two endpoints A, B in order to monitor differential delays, the timestamps sent and received from both ends, as both ends use the same time reference, characterized in that the time of the time stamp sent and received from both ends uses the same time reference. The differential delay measurement is performed by combining the results of the two measurements into a single number indicating a change in the differential delay compared to the differential delay at the beginning of the measurement.

Description

[0001] The present invention relates to a method for transmitting data between two endpoints A and B, which particularly requires a common time of day (TimeOfDay) at the two endpoints A and B in order to monitor differential delays. According to the characteristics of the general term of claim 1, the method sends and receives timestamps from both ends because both ends use the same time reference.

[0002] Current differential delay protection applications rely on equal communication delays between the two endpoints of the application. In the figure, the time it takes to transmit data from A to B should be the same (or have minimal variation) as the time it takes to transmit data from B to A. The difference between the two is called the differential delay of the service. The difference in transmission time in the two directions is called the differential delay of the service.

[0003] Current differential protection applications typically use protocols such as IEEE C37.94, which typically rely on TDM networks between the two ends. When these applications move to Ethernet-based communication infrastructure, they will take advantage of the TDMolP capabilities of Ethernet networks. These types of networks always have some jitter. In addition, the jitter of the TDMolP service depends on several factors, such as the addition of additional services on the network and the type of data used by other services.

[0004] When using current differential protection applications on Ethernet-based networks, the network must be able to control the differential protection. Typically, the maximum differential delay allowed is in the range of 50 microseconds to 400 microseconds. Preferably, the network has the ability to measure and / or monitor the differential delay and provide this information to the network users. This allows the user to detect any changes in the differential delay.

[0005] Differential Delay Measurement

[0006] In order to monitor differential delay without using external test equipment, the system usually needs to use a common time of day at both endpoints. It is easy to compare the send and receive timestamps from both ends because both use the same time reference. However, the accuracy of the measurement (microseconds) excludes simple time synchronization techniques of the two nodes, such as the Network Time Protocol. More precise mechanisms, such as GPS clocks at each node or time distribution using IEEE1588PTP, are usually complex and expensive.

[0007] In the above and below contexts, the terms "A end" and "end point A" are used equivalently. The same applies to "B end" and "end point B".

[0008] Therefore, the present invention is based on this problem and provides a simple time synchronization technology for two nodes (endpoints A and B) while at least maintaining the measurement accuracy (microsecond level).

[0009] This problem is solved by the features of patent claim 1.

[0010] According to the invention, a differential delay measurement is provided by combining the results of two measurements into a single number indicating the change in differential delay compared to the differential delay at the start of the measurement.

[0011] In order to eliminate the dependency on the IEEE 1588 PTP protocol, the solution according to the invention shows that it is only necessary to measure the variation of the differential delay over time without knowing the exact differential delay.

[0012] If the initial differential delay is too high, current differential protection applications do not work at startup. This does not usually result in a potential protection fault that could damage the distribution. However, knowing the change in differential delay is much more important than knowing the actual differential delay itself. The transition from a working condition (differential protection under control) to a non-working condition (differential protection out of range) has a much greater impact on the distribution network, as the protection application may perform unnecessary shutdowns on certain sections.

[0013] The present invention describes a solution (and therefore a method) for accurately measuring the change in differential delay in the case where the two end points do not have a common time of day. This means that the solution can be used when synchronous Ethernet is used, even when adaptive and internal clocks are combined. The solution also works when the synchronous Ethernet between the two ends fails and each end uses its own internal clock.

[0014] The differential delay measurement combines the results of two measurements to provide a single number that indicates the change in differential delay compared to the differential delay at the start of the measurement.

[0015] Both measurements are necessary, otherwise not all application cases can be measured accurately.

[0016] Measurement 1: Transmission delay variation between Side A and Side B.

[0017] The first measurement measures the variation in transmission delay between the two directions, but relies on the fact that both ends are synchronized (eg using Synchronous Ethernet).

[0018] · Both the A and B terminals have counters that increment with each cycle of their respective internal clocks.

[0019] · End A sends a message to End B at local time tA1.

[0020] · Terminal B receives the message at local time tB1 and acknowledges the message.

[0021] and include the value of tB1 in the message,

[0022] · End A receives the confirmation at local time tA2,

[0023] · End A calculates (i) the round trip time rA1 = tA2 - tA1 and (ii) the initial offset offsetA1 = tB1 - tA1 - rA1 / 2.

[0024] If the transmission time changes in one of the two directions and the measurement is repeated, the calculated offset (OffsetA2) changes. This can be used to indicate a change in the differential delay.

[0025] The absolute value of the change in differential delay can be calculated as follows:

[0026] ·ddA=2×(offsetA2-offsetA1)×internal clock cycle.

[0027] Measurement 2: Clock difference between A and B

[0028] If the two ends are no longer synchronized, the second measurement is used to correct the first measurement. In this case, the local time at both ends is no longer frequency synchronized, making the measurement of the transmission delay using measurement 1 unreliable.

[0029] To correct the results, measurement 2 compares the clock frequencies of both ends by looking at the internal send rate and the rate of incoming packets. The difference in the send rate and the receive rate provides the clock difference between the two ends. If the two ends are synchronized, the difference is 0 (for a long period of time) and the second measurement does not change the results of the first measurement.

[0030] The A side uses a counter ctrAA which increases with each cycle of its own clock.

[0031] The TDMoIP mechanism periodically sends data packets to the other party according to its own transmission clock. This means that packets are periodically sent from end A to end B and from end B to end A.

[0032] A uses a counter ctrAB, which is incremented each time a packet is received from B.

[0033] Calculation at end A: ctrDiffA = ctrAB - ctrAA.

[0034] Combination of two measurements:

[0035] To get the final result, terminal A must combine the results of the two measurements. This result is calculated as:

[0036] ·RelativeDifferentialDelay=ddA+2xctrDiffA.

[0037] This combination provides very accurate results, comparable to measurements using external test equipment.

Claims

1. A method for transmitting data between two endpoints A, B, in particular requiring a common time of day at the two endpoints A, B in order to monitor differential delays, the method sending and receiving timestamps from both ends, since both use the same time reference, It is characterized in that The differential delay measurement is made by combining the results of the two measurements into a single number that indicates the change in differential delay compared to the differential delay at the start of the measurement.

2. The method according to claim 1, It is characterized in that The transmission delay variation between the A end and the B end is determined by the first measurement, and the clock difference between the A end and the B end is determined by the second measurement.

3. The method according to claim 2, It is characterized in that The first measurement is performed as: Both A and B have counters that increment with each cycle of their respective internal clocks. Number, · End A sends a message to End B at local time tA1, ·B receives the message at local time tB1 and confirms the message, and sends The value of tb1 is included in the message, Terminal A receives the confirmation at local time tA2, and A calculates (i) the round trip time rA1 = tA2 - tA1 and (ii) the initial offset offsetA1=tB1-tA1-rA1 / 2.

4. The method according to claim 2 or 3, It is characterized in that The second measurement is used to correct the first measurement if the two ends are no longer synchronized, in which case the local times of the two ends are no longer frequency synchronized.

5. The method according to claim 4, It is characterized in that For result correction, the second measurement compares the clock frequencies of the two ends A, B by taking into account the internal sending rate and the rate of incoming packets, the difference in sending and receiving rates providing the clock difference between the two ends A and B.

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