JP7533733B2 - Communication Control Method - Google Patents

Description

This invention relates to a communication control method in a system using TSN (Time Sensitive Networking).

Conventional networks have adopted methods of adjusting bandwidth by setting priorities and widening the interval between transmission frames. However, there are restrictions such as limiting the amount of transmission in order to ease momentary congestion on the network and prevent frames from being discarded.

Therefore, a method is used to ensure that important data arrives reliably while transmitting large amounts of data using TSN time division. TSN is a network bandwidth control technology that uses time synchronization with PTP (IEEE 1588 Precision Time Protocol) and executes transmissions during time-division periods on the network using this highly accurate clock.

According to TSN, important data and other communication data (data other than important data: hereafter referred to as general data) are transmitted at different times, so the transmission of important data is not affected by the transmission of general data. For example, Patent Document 1 is a known example of TSN-related technology.

Patent Publication No. 2020-17877

(1) In conventional networks (networks that do not support TSN), when large amounts of data are transmitted, the buffers of network devices such as switching hubs (hereafter referred to as HUBs) can momentarily become insufficient, causing frames to be discarded. If important data is discarded at this time, it can cause problems. There are methods that use protocols to confirm delivery and resend data, but these methods take time due to timeout processing, etc., and are therefore not applicable to systems that require responsiveness.

As mentioned above, the network was designed to have sufficient capacity by making adjustments such as setting priorities to give priority to certain frames and spreading out the intervals between frames to send them more slowly. This design makes it impossible to transmit large amounts of data.

In contrast, a TSN network (a network compatible with TSN) transmits data in time-shared periods using a PTP time-synchronized clock. During the important data period determined by TSN, only important data is sent and received, so it is less susceptible to the effects of general data. However, during the period when general data is transmitted, each HUB transmits large amounts of data, so a mechanism such as delivery confirmation is required to avoid discarding frames due to high load.

(2) If all HUBs in a system are TSN-compatible, data types can be separated into time-shared periods. A new system can be built using only TSN-compatible HUBs, but in practice, it is common to update part of a legacy system to a TSN-compatible HUB.

Conventional networks that operate to keep transmission loads low coexist with TSN networks that are time-division separated by data type (important data/general data), and problems arise at the boundary between the two.

Conventional networks transmit only a small amount of data, less than 1% of the transmission path, and even in the rare cases when large amounts of data such as files are sent, measures such as bandwidth control are used to transmit data slowly, and timing control is also used to prevent multiple hubs from sending large amounts of data at the same time. On the other hand, TSN networks have ample transmission capacity during periods when important data is being sent and received, and are best-effort type during periods when general data is being sent, and the transmission load can approach 100% due to large amounts of data being sent.

At the boundary between these two networks, frames are discarded because the expected transmission conditions are not met. In addition, since TSN handles multiple transmission periods, the settings are complicated, and it would be a huge task to configure it while taking into account the conventional network.

(3) The present invention was made to solve such problems, and aims to automatically detect network devices that do not support TSN when conventional networks and TSN networks are mixed, and to deal appropriately with the boundary between the two.

(1) One aspect of the present invention is a method for detecting a network device in a system using Time Sensitive Networking (TSN), comprising:
obtaining information on the transmission and reception times of large and small UDP frames having different frame sizes from time stamps when the UDP frames are sent back and forth between the TSN-compatible network devices, and calculating a transmission time of each of the UDP frames based on the obtained information;
detecting the presence of N network devices that do not support TSN if the transmission time difference between the UDP frames is N times the frame size difference;
The present invention is characterized in that it has the following features.

(2) Another aspect of the present invention is a method for controlling communication of a time sensitive network device located at a boundary between a time sensitive network and a non-time sensitive network in a system using the time sensitive network, the method comprising:
A step of discarding frames of general data other than important data among the frames transmitted from the TSN-compatible network side, and transmitting only the frames of the important data to the TSN-incompatible network side;
transmitting the frames transmitted from the TSN non-compliant network side to the TSN compliant network side during a time-shared period of important data;
The present invention is characterized in that it has the following features.

(3) Yet another aspect of the present invention is a method for controlling communication of a time sensitive network device located at a boundary between a time sensitive network and a non-time sensitive network in a system using the time sensitive network, the method comprising:
a step of applying a bandwidth restriction to frames of general data other than important data among the frames transmitted from the TSN-compatible network side and transmitting the frames to the TSN-incompatible network side;
transmitting the frames transmitted from the TSN non-compliant network side to the TSN compliant network side during a time-shared period of important data;
A communication control method comprising:

(4) Yet another aspect of the present invention is a time synchronization method for a system using Time Sensitive Networking (TSN), in which a network device that does not support TSN exists between a network and a work device that supports TSN, comprising:
If there is a response to the PTP (Precision Time Protocol) time synchronization frame transmitted by the TSN-compatible network device, a PTP time synchronization frame is transmitted back and forth between the TSN-compatible network devices to perform time synchronization;
if there is no response, performing time synchronization by sending a UDP time synchronization frame back and forth between the TSN-compatible network devices;
A time synchronization method comprising:

According to the present invention, when conventional networks and TSN networks coexist, it is possible to automatically detect network devices that do not support TSN and to appropriately handle the boundary between the two.

FIG. 4 is a schematic diagram showing a transmission time when no conventional relay device exists between TSN relay devices in the first embodiment; FIG. 13 is a schematic diagram showing transmission time when a conventional relay device is present. 1 is a schematic diagram of a system in which TSN networks and conventional networks coexist. 1 is a graph showing a transmission load in a conventional network. 1 is a graph showing the transmission load through a TSN network. 1 is a graph showing a transmission load when a conventional network and a TSN network are mixed. FIG. 11 is a schematic diagram showing a communication control method A of the second embodiment. FIG. 4 is a schematic diagram showing the communication control method B of the same embodiment. FIG. 13 is a schematic diagram showing a case where a conventional relay device can transfer a time synchronization frame in the third embodiment. FIG. 13 is a schematic diagram showing a case in which the time synchronization frame cannot be transferred. FIG. 1 is a schematic diagram showing an industrial application field of the present invention. 12 is a schematic diagram showing a conversion process of the arrow Q in FIG. 11 .

The present invention relates to a technology for a system using TSN, and relates to a detection method for a TSN-compatible network device (TSN-compatible device) to detect a TSN-incompatible network device (TSN-incompatible device), a communication control method for TSN-compatible devices, and a time synchronization method. The following describes an embodiment of the present invention based on Examples 1 to 3.

In Example 1, the detection method is described. Here, the TSN-compatible device is a relay device (HUB: hereafter referred to as a TSN relay device) that supports TSN.

Devices that do not support TSN are called relay devices (HUBs) that do not support TSN, but to distinguish them from HUBs with PTP functionality, the ones without PTP functionality are called conventional HUBs, and the ones with PTP functionality are called PTP hubs.

<Basic Concept>
If a conventional HUB/PTP hub exists between the TSN relay devices, the TSN relay device detects the existence of the conventional HUB/PTP hub in order to perform operation processing according to the existence of the conventional HUB/PTP hub. Between the TSN relay devices, a PTP time synchronization frame according to the event type is sent back and forth by the PTP time synchronization function.

If a conventional hub exists between the TSN relay devices, the conventional hub will forward the frame without time correction. Since the time is not corrected, time synchronization will be unstable, but it is not possible to determine that a conventional hub exists. Even if a PTP hub exists between the TSN relay devices, the PTP hub will perform time correction and time synchronization will be stable, so it is not possible to determine that a PTP hub exists.

Therefore, we make it possible for TSN relay devices to perform time synchronization using normal UDP frames. UDP frames of different frame sizes are sent back and forth as time synchronization frames with timestamps attached.

In this case, if a conventional HUB/PTP hub exists between the TSN relay devices, it will be processed as a simple transfer, and a transmission time difference will occur depending on the size of the UDP frame. The presence of a conventional HUB/PTP hub is detected based on this transmission time difference.

If there is no adjacent TSN relay device, there will be no response to a normal UDP frame, but this will be interpreted as meaning that a conventional HUB/PTP hub or similar is connected.

<Details of the detection method>
The detection method will be described in detail with reference to Figures 1 and 2. In Figures 1 and 2, 1a and 1b indicate TSN relay devices 1. Also, 2 indicates a conventional HUB/PTP hub (hereinafter referred to as conventional HUB, etc. 2) that exists between the TSN relay devices 1a and 1b.

(1) Figure 1 shows the state in which a PTP time synchronization frame is sent back and forth between TSN relay devices 1a and 1b. Specifically, TSN relay device 1a sends a "Pdelay_Req" message to TSN relay device 1b. Upon receiving this message, TSN relay device 1b responds by sending back a "Pdelay_Resp" message.

The transmission and reception times "T1" to "T4" for the outbound and inbound journeys are obtained based on the timestamps when such a PTP time synchronization frame travels back and forth, and the transmission time between TSN relay devices 1a and 1b is calculated. Note that the calculated transmission time is the timing when the first part of the frame is transmitted and received, as a timestamp mechanism is used, and is not affected by the frame size.

(2) Figure 2 shows a state in which UDP frames of different frame sizes are sent back and forth between TSN relay devices 1a and 1b as time synchronization frames. Here, the conventional hub 2 transfers each UDP frame without time correction. However, the transfer time of the conventional hub 2 differs depending on the size of each UDP frame.

For example, if a 100-byte UDP frame and a 1,000-byte UDP frame are sent back and forth, if there is a conventional hub or similar device 2 along the way, the store-and-forward mechanism adds the frame size to the sending and receiving time, affecting the transmission time of each.

The transmission time is calculated on the TSN relay device 1a side in the same way as for the PTP time synchronization frame. That is, the sending and receiving times "T1" to "T4" for the outbound and return journeys are obtained based on the timestamps when each UDP frame is sent back and forth, and the transmission time of each UDP frame is calculated using formula (1).

Equation 1: Transmission time = (T2 - T1) + (T4 - T3) / 2
T1 = Time when outgoing UDP frame is sent T2 = Time when outgoing UDP frame is received T3 = Time when returning UDP frame is sent T4 = Time when returning UDP frame is received The TSN relay device 1a detects the number of conventional hubs, etc. 2 according to the transmission time difference (delay time) between the outgoing and returning paths calculated by formula 1. In other words, if the "transmission time difference = N times the frame size difference", it is determined that there are N conventional hubs, etc. 2 between the TSN relay device 1b. For example, in the case of the aforementioned UDP frames (100 bytes/1000 bytes), the frame size difference is "900 bytes".

If the transmission time difference is "900 bytes", it is one time the frame difference, so it is determined that one conventional HUB etc. 2 exists. Also, if the transmission time difference is "1800 bytes", it is twice the frame difference, so it is determined that two conventional HUB etc. 2 exist.

If the transmission time difference is not an integer multiple of the frame difference, a fractional processing method (such as rounding off) may be used. Also, if the "transmission time difference ≒ 0", it is determined that the conventional HUB etc. 2 does not exist.

As described above, according to the first embodiment, it is possible to determine whether or not a conventional hub 2 exists between the TSN devices 1a and 1b. In other words, since the presence of a conventional hub 2 can be detected, any changes to the network configuration can be automatically accommodated. This reduces configuration errors and improves system stability. In addition, it is possible to distinguish a PTP hub as a device that does not support TSN, and it is also possible to detect devices that operate as bridges other than hubs.

The second embodiment will be described with reference to Figures 3 to 8. In this embodiment, a communication control method will be described for a case where a conventional network and a TSN network are mixed.

In other words, if multiple conventional hubs, etc. 2 can be detected by the detection method of the first embodiment, it can be recognized that a conventional network 20 and a TSN network 10 are mixed, as shown in Figure 3. In Figure 3, 1 indicates a TSN relay device that constitutes the TSN network 10, and 2 indicates a conventional hub, etc. 2 that constitutes the conventional network 20.

Figure 4 shows the transmission load in a conventional network. Here, transmission is adjusted to the minimum necessary so that frames are not discarded due to momentary high loads.

Figure 5 shows the transmission load of the TSN network, with important data period J and general data period I as time-division periods. This general data is subject to delivery confirmation by TCP and other protocols, and frame discarding due to high load is permitted.

When the conventional network 20 and the TSN network 10 are connected, the transmission load in FIG. 4 and the transmission load in FIG. 5 are added together, resulting in the transmission load shown in FIG. 6, which may result in some of the important data transmitted over the conventional network 20 being discarded. The probability that a frame will be discarded is a fixed probability per frame, but since the number of frames of important data is small, the impact is relatively large.

Therefore, in this embodiment, when a conventional network 20 and a TSN network 10 are mixed, the following communication control methods A and B are implemented to adjust the transmission timing and bandwidth at the boundary between the two networks 10 and 20.

(1) Communication control method A
First, a description will be given of the communication control method A. At the boundary between the two networks 10, 20, there is a risk that the conventional network 20 will be overwhelmed by a large amount of general data transmitted from the TSN network 10 side.

Therefore, among the frames sent from the TSN network side, frames containing general data are discarded at the boundary and are not sent to the conventional network 20 side. On the other hand, frames sent from the conventional network 20 side are transmitted to the TSN network side during the period of important data. One method is to discard all general data sent from the conventional network 20 side, or to prepare a dedicated transmission period in the TSN network and collect it there.

The details will be explained based on Figure 7. In Figure 7, 1c indicates a TSN relay device 1 located at the boundary between the two networks 10, 20. 1d and 1e indicate TSN relay devices 1 located on the TSN network side of TSN relay device 1c. 2a and 2b are conventional hubs, etc. 2 located on the conventional network side, adjacent to TSN relay device 1c.

Here, general data frames transmitted and received in the order of TSN relay devices "1e → 1d → 1c" on the TSN network 10 side are discarded by TSN relay device 1c and are not forwarded to conventional hub etc. 2a on the conventional network 20 side.

On the other hand, frames transmitted and received in the order of "conventional hub 2b → 2a" on the conventional network 20 side are sent from conventional hub 2a to TSN relay device 1c. TSN relay device 1c receives the frames, stores them as important data, and transmits them to TSN relay device 1d during the important data period of the TSN.

At this time, the TSN relay device 1c sets the transmission bandwidth low to ensure stable transmission during the period of important TSN data, or adjusts the schedule to ensure even transmission.

In addition, in FIG. 7, data sent from the conventional network 20 arrives at the TSN network 10 with a slight delay, and high-load transmission of general TSN data is limited to only the TSN network 10 section.

(2) Communication control method B
The communication control method B will be described with reference to Fig. 8. Among frames transmitted and received in the order of TSN relay devices "1e -> 1d ->1c" on the TSN network 10 side, general data frames are band-limited by TSN relay device 1c and then transmitted to the conventional network 20 side (conventional HUBs 2a, 2b, etc.).

In other words, while a large amount of general data can be transmitted within the TSN network 10, the amount of general data transmitted within the conventional network 20 is limited to a small amount. At this time, the width of the communication path changes at the boundary (TSN relay device 1c), and communication with a narrow bandwidth is easily affected by bandwidth adjustment by TCP.

Therefore, the bandwidth of general data on the networks 10 and 20 sides is adjusted so that frames are not discarded even when TSN general data is sent to the conventional network 20. This reduces the impact on the conventional network 10 and enables communication throughout the entire system. Note that frames from the conventional network 20 side are processed in the same way as in communication control method A.

According to the second embodiment, in an environment where a conventional network 20 and a TSN network 10 coexist, communication via the TSN relay device 1 is possible, albeit with restrictions, while maintaining communication via the conventional network 20.

Note that communication control methods A and B are executed at the boundary when conventional hubs, etc. 2 are detected by Example 1, and return to normal TSN operation when all conventional hubs, etc. 2 are removed. This normal TSN operation can be used without bandwidth restrictions.

The third embodiment will be described with reference to Figures 9 and 10. This embodiment mainly relates to a PTP time synchronization method when a conventional HUB or the like 2 is detected between TSN relay devices 1a and 1b by the detection method of the first embodiment.

The PTP time synchronization between the TSN relay devices 1a and 1b is performed by exchanging "Pdelay_Req" and "Pdelay_Resp" messages, as shown in Figure 9. However, although the standard for PTP time synchronization is multicast by L2 (Layer 2), as shown in Figure 10, there are cases where the conventional HUB etc. 2 between the TSN relay devices 1a and 1b is a device that does not forward the above messages.

Therefore, if there is no "Pdelay_Resp" message response to the "Pdelay_Req" message (PTP time synchronization frame) within a specified time, the TSN relay device 1a will time out.

In addition, in the event of a timeout, the TSN relay device 1a changes to a predetermined UDP frame and sends a time-synchronized "Pdelay_Req" message to the TSN relay device 1b.

At this time, if the TSN relay device 1a receives a "Pdelay_Resp" message (UDP frame) response from the TSN relay device 1b, it performs time synchronization using a UDP frame. If there is no "Pdelay_Resp" message (UDP frame) response, it determines that there is no adjacent TSN relay device 1b, and does not perform time synchronization.

Specifically, the third embodiment is carried out in the following procedure.
(1) The TSN relay device 1a transmits normal UDP time synchronization frames in large and small frame sizes.
(2) If there is no response to the transmission, the TSN relay device 1a determines that there is no TSN relay device 1 at the destination, and does not perform time synchronization.
(3) If there is a response from the TSN relay device 1b, it is determined by the detection method of the first embodiment whether or not a conventional hub or the like 2 is present in between.
(4) If the result of the above determination is that no conventional hub or the like 2 exists, time synchronization is performed between the TSN relay devices 1a and 1b using a normal PTP time synchronization frame.
(5) If the result of the above determination is that a conventional hub or the like 2 exists, the TSN relay device 1a transmits a normal PTP time synchronization frame (a "Pdelay_Req" message) to the TSN relay device 1b.

If there is a response from the TSN relay device 1b with a PTP time synchronization frame (a "Pdelay_Resp" message), time synchronization is performed between the regular PTP time frames. On the other hand, if there is no response with the PTP time synchronization frame, time synchronization is performed using a normal UDP time synchronization frame. Therefore, according to the third embodiment, time synchronization is possible in the case where the conventional hub etc. 2 does not forward the PTP time synchronization frame.

In Patent Document 1, as shown by the arrow Q in Figures 11 and 12, the TSN relay device 1f performs time-division transmission on behalf of the TSN-incompatible device 12 as a conversion process to make the TSN-incompatible device 12 compatible with TSN.

In contrast, according to the present invention, in an environment where both networks 10 and 20 coexist, the TSN relay device 1c located at the boundary indicated by the arrow P in FIG. 11 detects the conventional hub 2, and further enables frame communication control and time synchronization.

Therefore, the present invention can appropriately respond to an environment in which a TSN network 10 and a conventional network 20 coexist, and is industrially beneficial.

1, 1b, 1c, 1d, 1e, 1f...TSN relay device 2, 2a, 2b, 2c...conventional hub, etc. 11...TSN compatible device 12...conventional device 10...TSN network 20...conventional network

Claims (2)

A method for controlling communication of a time sensitive network device located at a boundary between a time sensitive network and a non-time sensitive network in a system using the time sensitive network, comprising:
A step of discarding frames of general data other than important data among the frames transmitted from the TSN-compatible network side, and transmitting only the frames of the important data to the TSN-incompatible network side;
transmitting the frames transmitted from the TSN non-compliant network side to the TSN compliant network side during a time-shared period of important data;
A communication control method comprising: A method for controlling communication of a time sensitive network device located at a boundary between a time sensitive network and a non-time sensitive network in a system using the time sensitive network, comprising:
a step of applying a bandwidth restriction to frames of general data other than important data among the frames transmitted from the TSN-compatible network side and transmitting the frames to the TSN-incompatible network side;
transmitting the frames transmitted from the TSN non-compliant network side to the TSN compliant network side during a time-shared period of important data;
A communication control method comprising:

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