CN112202519A - Method for controlling message transmission delay jitter - Google Patents
Method for controlling message transmission delay jitter Download PDFInfo
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- CN112202519A CN112202519A CN202010871162.8A CN202010871162A CN112202519A CN 112202519 A CN112202519 A CN 112202519A CN 202010871162 A CN202010871162 A CN 202010871162A CN 112202519 A CN112202519 A CN 112202519A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0658—Clock or time synchronisation among packet nodes
- H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
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Abstract
The invention relates to the field of digital substations, in particular to a method for controlling message transmission delay jitter, which comprises the following steps: synchronizing the time and frequency of all devices on the link; the transmission delay of each message on a link and the residence time of each message in each device are measured by stamping a timestamp on each message, and the delay time of each message on the whole link is calculated; setting a fixed delay time according to the delay time of each message on the whole link; and transmitting the message when the fixed delay time is reached. The invention can control the message jitter delay within a small range.
Description
Technical Field
The invention relates to the field of digital substations, in particular to a method for controlling message transmission delay jitter.
Background
At present, a communication platform of a digital substation basically adopts a mode that a switch network consists of an SMV (simple message service) network, an MMS (multimedia messaging service) network and a GOOSE (generic object oriented substation event) network. The MMS network is used for the communication between the devices of the layer and the monitoring background, and the GOOSE network is used for the communication between the devices of the layer and the devices of the process layer.
SV samples the sampling frequency for protection and measurement is 4000Hz, i.e. the phase difference between two samples is 250 us. The maximum value of SV message jitter which can be tolerated by protection and measurement control is 10 us.
However, the communication devices in the existing substation mostly employ the switch and the EPON system. Both of them adopt best effort transmission mode, and it is difficult to effectively control the transmission of data signal in delay and delay jitter, and the jitter is usually much larger than 10 us. Jitter can reach the level of 100us when traffic bursts or large flows are encountered.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for controlling packet transmission delay jitter, so as to reduce the delay jitter of a packet in the transmission process.
The method for controlling the message transmission delay jitter comprises the following steps:
synchronizing the time and frequency of all devices on the link;
the transmission delay of each message on a link and the residence time of each message in each device are measured by stamping a timestamp on each message, and the delay time of each message on the whole link is calculated;
setting a fixed delay time according to the delay time of each message on the whole link;
and transmitting the message when the fixed delay time is reached.
Preferably, the time of all devices on the synchronization link includes:
the time of all devices on the link is synchronized via the 1588 protocol.
Preferably, the frequencies of all devices on the synchronization link include:
the frequencies of all devices on the link are synchronized by synchronous ethernet technology.
Preferably, the measuring the residence time of each packet in each device includes:
at the entrance of ONUx, a time stamp T for entering the ONUx is printed by a message through the local clock of the ONUx1When the message is about to be output through the PON, the residence time t of the message in the OUNx is calculated by checking the time of the local clock1；
At PON exit of ONUx, the residence time t1Put into the message, and simultaneously record the time stamp T of the message sent from ONUx from PON2Will time stamp T2MPCP _ rtt _ ts timestamp T put into MPCP packet3Performing the following steps;
the message is switched to another ONUy after passing through the OLT, and when the message reaches the PON port of the ONUy, the time stamp T of the arrival of the message is recorded4Using time stamp T4Minus the timestamp T of mpcp _ rtt _ ts in the message3Obtaining the residence time t of the message in the OLT2；
When the message enters from PON of ONUy and is output from GE port of ONUy, the time stamp T is used when the message is output5Minus the timestamp T of the incoming message6Obtaining the residence time t of the message in the ONUy3。
Preferably, the calculating the delay time of each packet on the whole link includes:
and calculating the sum of the total transmission delay of the message on the link and the total residence time of the message in each device to obtain the delay time of the message on the whole link.
Preferably, the fixed delay time is slightly greater than or equal to the maximum delay time of the message on the whole link.
By using the present invention, the following effects can be achieved:
1. the time and frequency of all equipment on the link are synchronized, so that the accuracy requirements of subsequent delay measurement and timestamp stamping are guaranteed, and the delay jitter control accuracy of the message is improved;
2. the method comprises the steps of stamping a timestamp on each message, measuring the transmission delay of each message on a link and the residence time of each message in each device, calculating the delay time of each message on the whole link, setting a fixed delay time according to the delay time of each message on the whole link, and transmitting the message when the fixed delay time is reached so as to control the message jitter delay within a small range.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is a schematic flowchart of a method for controlling packet transmission delay jitter according to an embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited to these embodiments.
In a general network technology, if the network is an ethernet switch, controllability of traffic transmission is improved by improving a traffic class of an SV. For example, on the input side, the flow classification ensures that the input side of the SV service does not lose packet due to speed limit, and ensures the reliability of the input signal. But in the case of a traffic burst, even with a priority guarantee, this can lead to data congestion buffering. Although the packet is not lost, the buffering of the service is also caused, which results in an increase in delay and an increase in uncertainty of the service path transmission. On the output side, the output is also scheduled by priority of the traffic. Therefore, the certainty of the service output can be ensured to a certain extent, and the uncertainty of the output of the service due to service congestion and the like is reduced.
The method ensures the certainty of service transmission by improving the service priority and preferentially scheduling data scheduling, thereby reducing the jitter delay of the service. But due to best effort ethernet data, non object oriented transport mechanisms lead to uncertainty in the transport delay of the data network. Although the priority scheduling is performed in each input and output link, in the case of congestion burst, in order to ensure that the service is not lost, a data buffering manner is adopted to buffer in advance, and when the congestion burst and the burst pass, a mechanism of sending a message again inevitably causes uncertainty of transmission delay of the service, thereby causing excessive delay jitter.
The basic idea of the invention is to synchronize the time and frequency of all devices on the link, and to provide guarantee for the accuracy requirements of the subsequent delay measurement and time stamping. And then, stamping a timestamp on each message, measuring the transmission delay of each message on a link and the residence time of each message in each device, calculating the delay time of each message on the whole link, setting a fixed delay time according to the delay time of each message on the whole link, and transmitting the message when the fixed delay time is reached, so that the delay jitter of the message is controlled within a minimum time range, and the requirement of a power system on the delay jitter of the message is well met.
Based on the above thought, an embodiment of the present invention provides a method for controlling packet transmission delay jitter, as shown in fig. 1, including the following steps:
s1: the time and frequency of all devices on the link are synchronized.
Specifically, the clock server supporting the 1588 protocol transmits the clock information to the OLT through an ethernet interface or a 1PPS + TOD interface. The OLT operates a 1588 protocol, synchronizes the local clock 2 with the clock 1, and transmits corresponding time information to the ONU through the PON port. A1588 protocol is operated between the OLT and the ONU, finally, the clock 3 of the ONU can be synchronized with the clock 2 by measuring and calculating line delay and time synchronization information, and finally, the clocks 1,2 and 3 realize synchronization by primary-level clock synchronization.
In order to improve the precision of clock synchronization, the ONU is enabled to finally realize the frequency synchronization of the ONU and the OLT by recovering the frequency of the PON through a synchronous Ethernet technology.
After the frequency synchronization is realized, the precision of the time clocks 1,2 and 3 reaches +/-100ns, and the precision requirements of subsequent time delay measurement and time stamping are guaranteed.
S2: and (3) stamping a timestamp on each message, measuring the transmission delay of each message on the link and the residence time of each message in each device, and calculating the delay time of each message on the whole link.
The transmission time of the message on the link can be calculated according to the timestamp of the message when the message is output by one device and the timestamp of the message when the message enters the next device.
At the entrance of ONUx, a time stamp T for entering the ONUx is printed by a message through the local clock of the ONUx1When the message is about to be output through the PON, the residence time t of the message in the OUNx is calculated by checking the time of the local clock1(ii) a At PON exit of ONUx, the residence time t1Put into the message, and simultaneously record the time stamp T of the message sent from ONUx from PON2Will time stamp T2MPCP _ rtt _ ts timestamp T put into MPCP packet3Performing the following steps; the message is switched to another ONUy after passing through the OLT, and when the message reaches the PON port of the ONUy, the time stamp T of the arrival of the message is recorded4Using time stamp T4Minus the timestamp T of mpcp _ rtt _ ts in the message3Obtaining the residence time t of the message in the OLT2(ii) a When the message enters from PON of ONUy and is output from GE port of ONUy, the time stamp T is used when the message is output5Minus the timestamp T of the incoming message6Obtaining the residence time t of the message in the ONUy3。
S3: and setting a fixed delay time according to the delay time of each message on the whole link.
Because the delay of each SV message in the whole link is not uniform, delay jitter is caused. In order to control the delay jitter within a small range, each SV message is sent to the client terminal equipment from the ONU side after a fixed delay as much as possible.
And calculating the sum of the total transmission delay of the message on the link and the total residence time of the message in each device to obtain the delay time of the message on the whole link. The setting of the fixed delay time is generally slightly larger than the maximum delay time of the message on the whole link.
The ONU adopts a message processing mode of storage forwarding, for messages with 64 bytes to 1518 bytes, the time delay of receiving the messages by a user port of the ONU is 0.672 us-12.304 us (GE port), and the internal processing time of the messages on the ONU is not more than 5 us. The ONU waits for the transmission window for no more than 125us upstream (the OLT allocates an upstream transmission window to each ONU with a fixed period of 125 us). The forwarding time delay of the switch does not exceed 30 us; the distance between the OLT and the ONU does not exceed 1 kilometer, and the optical fiber delay does not exceed 10 us; for messages with 64 bytes to 1518 bytes, the time delay of receiving the messages by the PON port of the ONU needs 0.672us to 12.304us (PON port), and the internal processing time of the messages in the downstream line of the ONU does not exceed 5 us. Total time delay: the Tdelta is 12.304+5+125+30+10+12.304+ 5-199.608 us, and if the ONU has a short congestion upstream, waits 2 upstream window times, then the Tdelta is 12.304+5+125+ 2+30+10+12.304+ 5-324.608 us.
The fixed delay time is slightly larger than or equal to the maximum delay time of the message on the whole link, so that an integer is selected, and the message is sent to the client terminal from the ONU side after the fixed delay time of the whole link is determined to be 325 us.
And when the message is advanced, subtracting the residence time of the message by 325us to obtain the waiting time of the ONU. And sending the message out of the ONU once the waiting time is over. By ensuring the frequency synchronization and the time synchronization of all the terminal devices of the system, the time delay jitter of the message can be finally ensured to be within 1 us.
S4: and transmitting the message when the fixed delay time is reached.
Since the delay of each message from ONU 1-ONU 2 will be different, the delay will vary within a range. In order to ensure that the time delay jitter index of the message is as small as possible, the time delay jitter index meets 10us of a power system. When the ONU2 sends a message to the terminal device, it is ensured as much as possible that the message is sent out at a fixed delay time. For example, some messages from ONU1 to ONU2 take only 201us, some take only 250us, and some take only 120 us. But the maximum theoretical delay would not exceed 300 us. Therefore, all messages are uniformly transmitted to the terminal equipment after the delay time of 300 us. For example, 120us of some messages reach ONU2, and then the messages are buffered for another 180us, and the messages are not sent from ONU2 to the terminal device until 300 us. Therefore, the time delay of receiving all messages by the terminal equipment can be controlled to be 300us, and the jitter time delay can be well controlled to be in a small range.
In some embodiments, the forwarding priority of the SV message can be ensured by increasing the priority of the SV message, so that the delay certainty and controllability of the SV message are increased, and the delay jitter of the SV message is ensured.
It should be noted that the invention can be applied to the delay control of messages such as SV/GOOS and the like of the power system, and can also be applied to the delay jitter control of messages of other data communication networks; meanwhile, the delay jitter decision method can be applied to any data exchange network except the PON system of OLT + ONU.
Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (6)
1. A method for controlling message transmission delay jitter is characterized by comprising the following steps:
synchronizing the time and frequency of all devices on the link;
the transmission delay of each message on a link and the residence time of each message in each device are measured by stamping a timestamp on each message, and the delay time of each message on the whole link is calculated;
setting a fixed delay time according to the delay time of each message on the whole link;
and transmitting the message when the fixed delay time is reached.
2. The method according to claim 1, wherein the synchronizing the time of all devices on the link comprises:
the time of all devices on the link is synchronized via the 1588 protocol.
3. The method according to claim 1, wherein the frequencies of all devices on the synchronization link include:
the frequencies of all devices on the link are synchronized by synchronous ethernet technology.
4. The method of claim 1, wherein the measuring the residence time of each packet in each device comprises:
at the entrance of ONUx, a time stamp T for entering the ONUx is printed by a message through the local clock of the ONUx1When the message is about to be output through the PON, the residence time t of the message in the OUNx is calculated by checking the time of the local clock1；
At PON exit of ONUx, the residence time t1Put into the message, and simultaneously record the time stamp T of the message sent from ONUx from PON2Will time stamp T2MPCP _ rtt _ ts timestamp T put into MPCP packet3Performing the following steps;
the message is switched to another ONUy after passing through the OLT, and when the message reaches the PON port of the ONUy, the time stamp T of the arrival of the message is recorded4Using time stamp T4Minus the timestamp T of mpcp _ rtt _ ts in the message3Obtaining the residence time t of the message in the OLT2；
When the message enters from PON of ONUy and is output from GE port of ONUy, the time stamp T is used when the message is output5Minus the timestamp T of the incoming message6Obtaining the residence time t of the message in the ONUy3。
5. The method of claim 1, wherein the calculating the delay time of each packet on the entire link comprises:
and calculating the sum of the total transmission delay of the message on the link and the total residence time of the message in each device to obtain the delay time of the message on the whole link.
6. The method of claim 1, wherein the fixed delay time is slightly longer than or equal to a maximum delay time of the packet on the entire link.
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