Real-time Stream Instantaneous Fault Tolerant Scheduling Method for IEEE 802.1 Qch

Abstract

The real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch of the present invention includes the following steps: Step 1: Input the real-time stream set, network topology, failure rate, safety standards for different critical levels, and time slot length; Step 2: Calculate the minimum number of redundant copies of the frames of real-time streams with different critical levels when meeting the safety standards; Step 3: Calculate the duration required for transmitting a TT stream or an AVB stream based on the minimum number of redundant copies of the frames calculated in Step 2, and allocate network resources for the TT stream and the AVB stream according to the rule that the TT stream and the AVB stream are stored in different queues and the TT stream is preferentially transmitted; Step 4: Schedule the TT stream and the AVB stream through the network resources allocated in Step 3, and calculate the probability of transmission failure per hour of the TT stream and the AVB stream during actual transmission; Step 5: Whether the probability of transmission failure per hour of the TT stream and the AVB stream meets the safety standards. If both are yes, return success; otherwise, return failure.

Description

Technical Field

[0001] The present invention belongs to the technical field of fault-tolerant scheduling of real-time networks, and relates to a method for fault-tolerant scheduling of instantaneous faults of real-time streams for IEEE 802.1Qch. Background Art

[0002] With the further deepening and reform of industrial digitization and informatization, the types of services in industrial information systems and control systems are constantly increasing, and industrial information networks and control networks also show a trend of integration. Services with different requirements need to be transmitted in a mixed manner. The key technical basis for realizing the mixing of information networks and control networks is Time-Sensitive Networking (TSN).

[0003] On the other hand, in scenarios such as autonomous driving and industrial automation systems, the reliability and real-time performance of network data transmission are crucial. However, in the automotive driving or complex industrial production environment, due to instantaneous faults (such as electromagnetic interference) or permanent faults (such as switch paralysis or network cable interruption), the transmission of network data is affected, resulting in system failure, casualties, industrial production interruption or even more serious accidents. Therefore, it is necessary to adopt the fault-tolerant scheduling of real-time streams of TSN to improve the reliability and real-time performance of network data transmission. Generally, the fault-tolerant scheduling of real-time streams of TSN can be divided into two levels: time redundancy and space redundancy.

[0004] At the time redundancy level, it often solves the instantaneous faults that occur during the network data transmission process. Traditional Ethernet solves such problems through the fault-tolerant mechanism of cyclic redundancy check and automatic repeat request, but retransmission will increase the transmission delay and cause uncertainty in network transmission. Alvarez et al. Inés,et al.Towards a timeredundancy mechanism for critical frames in Time-Sensitive Networking[C].ETFA2017.IEEE,2017:1-4) proposed an algorithm for proactive fault-tolerant scheduling to solve instantaneous faults. Its main idea is to transmit multiple copies of real-time stream frames on a route to improve the reliability of data transmission in time-sensitive networks. Alvarez et al. proposed two schemes. One is that the source terminal directly copies a certain number of real-time stream frame copies and transmits them on a route; the other is that intermediate node devices on a route respectively copy a certain number of real-time stream frame copies and eliminate the received frame copies. Based on this method, the probability of multiple copies of frames simultaneously being in error during the network data transmission process is relatively low, thereby improving the reliability of network data transmission.

[0005] At the spatial redundancy level, the TSN working group proposed the IEEE 802.1CB standard (IEEE Standard for Local and metropolitan area networks—Frame Replication and Elimination for Reliability) to improve the transmission reliability of TSN. Relay devices that meet the frame replication and elimination mechanism in the IEEE 802.1CB standard can actively replicate frames and eliminate frame copies. Based on this, before real-time stream transmission, multiple non-intersecting routes can be allocated for the real-time stream; at the start of real-time stream transmission, the node device connected to the source terminal will actively replicate n copies of the frame to be transmitted (the value of n is determined by the number of non-intersecting routes); during the real-time stream transmission process, each copy of the frame is transmitted along its respective route to the node device connected to the destination terminal; this node device will actively eliminate the frame copies and transmit the earliest-arrived and correct frame to the terminal.

[0006] At the temporal redundancy level, both of the two schemes in the active fault-tolerant scheduling algorithm proposed by Alvarez et al. require transmitting multiple copies of a frame in the network link at one time. However, since the number of transmission copies of real-time stream frames is not determined, it will not be possible to ensure that the reliability and schedulability requirements of network data transmission are both met. Although transmitting multiple copies of real-time stream frames can improve the network reliability, this will reduce the network schedulability, that is, it cannot satisfy the constraint that all copies of all real-time streams in the network system arrive at the destination node before their deadlines at the same time. On the contrary, reducing the number of copies of real-time stream frames can improve the network schedulability, but the network reliability cannot be guaranteed.

[0007] At the spatial redundancy level, the IEEE 802.1CB standard proposed by the TSN working group has similar deficiencies to the active fault-tolerant scheduling algorithm proposed by Alvarez et al. Using the method proposed in the IEEE 802.1CB standard, multiple non-intersecting routes need to be allocated for each real-time stream. Non-intersecting routes mean that except for the source terminal node and the destination terminal node of the route being the same, there are no intersecting intermediate nodes. Obviously, the network load of each route or each link segment will increase, so when the network reliability conditions are met, the network schedulability will decrease. On the contrary, reducing the number of routes for each real-time stream can improve the network schedulability, but the network reliability cannot be guaranteed. Summary of the Invention

[0008] To solve the above technical problems, the object of the present invention is to provide a real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch. By introducing a probability model of instantaneous faults occurring in network transmission and safety standards for real-time streams of different critical levels, the number of retransmissions of real-time stream frames is quantified, and the pain point of being unable to balance the reliability and schedulability of real-time stream transmission in TSN fault tolerance scheduling is solved.

[0009] The present invention provides a real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch, including:

[0010] Step 1: Input a set of real-time streams, network topology, failure rate, safety standards for different critical levels, and time slot length. The real-time streams include TT streams and AVB streams, and the critical level of TT streams is higher than that of AVB streams;

[0011] Step 2: Calculate the minimum number of redundant copies of frames of real-time streams of different critical levels when meeting the safety standards;

[0012] Step 3: Calculate the duration required for the transmission of a TT stream or an AVB stream based on the minimum number of redundant copies of frames calculated in Step 2. According to the rule that TT streams and AVB streams are stored in different queues and TT streams are preferentially transmitted, allocate network resources for TT streams and AVB streams;

[0013] Step 4: Schedule TT streams and AVB streams using the network resources allocated in Step 3, and then calculate the probability of transmission failure per hour of TT streams and AVB streams during actual transmission;

[0014] Step 5: Whether the probability of transmission failure per hour of TT streams and AVB streams meets the safety standards. If both are yes, return success; otherwise, return failure.

[0015] In the real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch of the present invention, the safety standards for different critical levels are specifically:

[0016] To describe the reliability of network transmission, the probability of failure per hour PFH is introduced as a safety standard index, and three critical levels A, B, and C in the DO-178B standard are used to measure the reliability of real-time stream transmission. The PFH requirements for the three critical levels are PFH(A) < 10 -9 、PFH(B) < 10 -7 、PFH(C) < 10 -5 ; TT streams belong to level A or B, and AVB streams belong to level C.

[0017] In the real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch of the present invention, the switches in the network topology support the functions of cyclic redundancy check and automatic repeat request.

[0018] In the real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention, the failure rate refers to the frequency of a frame transmission failure in a link, and the exponential distribution is used to represent the probability of instantaneous fault occurrence during the transmission of the real-time stream.

[0019] In the real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention, the specific content of step 2 is as follows:

[0020] Step 2.1: The probability of hourly transmission failure of the TT stream or AVB stream is calculated according to formula (1):

[0021]

[0022] where, pfh(x) represents the set S of real-time streams with the critical level of x x The probability of hourly transmission failure; x represents the critical levels A, B, or C; represents the probability that all frames of a real-time stream S i are transmitted and failed in a route; r i (n i , t) represents the number of times a real-time stream S i is released within the time t, and t takes the value of 1 hour;

[0023]

[0024] where, represents the probability that the j-th frame of a real-time stream S i is transmitted and failed on the link [v a , v b , and the value range is [0, 1], NF i is the number of frames in a real-time stream S i ;

[0025]

[0026] where, λ is the failure rate, which is set by the user according to the working scenario of the device; is the transmission time of the frame on this link, which is determined by the length of the frame and the parameters of the port; e is the natural constant;

[0027]

[0028] where, C i represents the total transmission duration of the real-time stream S i , that is, the sum of all link transmission times; n i represents the real-time stream S released once iThe number of copies of the frames; T i is the real-time stream S i 's period;

[0029] Step 2.2: Introduce a real-time stream S i The maximum probability that all frames of are transmitted unsuccessfully in one route and the set S of real-time streams with critical level x x The maximum probability of transmission failure per hour Calculate the minimum redundant copy number of real-time stream frames for each critical level:

[0030] If pfh(x) has an upper limit and the upper limit meets the corresponding reliability requirements, then the transmission of real-time streams at this level is reliable. Introduce the following formula:

[0031]

[0032] where, represents the maximum value of the probability of transmission failure of the j-th frame of the real-time stream S i in one route, that is, the maximum value of Equation (3); is determined by the parameter λ and the transmission time of the real-time stream in one link. That is, when λ is the largest and the transmission time in one link is the longest, is the maximum value, and the link with the longest transmission time is denoted as When reaches the maximum value, the transmission time of each link needs to be the maximum value. Then at this time, each link is represents the number of such links in this route ;

[0033]

[0034] When , that is, the theoretical maximum value of the probability of real-time stream transmission failure meets the reliability requirements, and the actual transmission failure probability of the real-time stream will not be greater than Therefore, the transmission of all real-time streams at this level is reliable; x in PFH(x) represents the critical level A, B, or C; for the convenience of calculation, it is stipulated that real-time streams at the same level have the same redundant copy number, that is, when x is the same, n i is the same. At this time, the minimum value of the number of copies n of the frames of the real-time stream can be derived from i , that is, the minimum redundant copy number.

[0035] In the real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch of the present invention, the said step 4 includes:

[0036] Step 4.1: Calculate the probability of hourly transmission failure of TT streams and AVB streams during actual transmission according to formula (1);

[0037] Step 4.2: When an AVB stream cannot complete transmission before its deadline, terminate or degrade the service of the AVB stream. Calculate the probability of hourly transmission failure pfh'(x) when the AVB stream is terminated through the following formula:

[0038]

[0039] where P(N', α) represents the minimum probability that all TT streams have successful transmission of the first n i copies within the time interval [0, α]; represents the maximum probability of transmission failure of all frames of an AVB stream S k in one route; n k represents the number of copies of the frames of an AVB stream S k released once; when pfh'(x) < PFH(x), the transmission of the AVB stream is reliable;

[0040]

[0041] P(N', t) represents the minimum probability that all TT streams have successful transmission of the first n i -1 copies within the time interval [0, t], and at this time, the transmission of the AVB stream will not be affected by TT streams;

[0042]

[0043] where, P k (t) represents the set of the latest completion times of each released frame of an AVB stream S k within the time interval [0, t]; C k represents the total transmission duration of the AVB stream S k , T k and D k are the period and deadline of the AVB stream S k respectively; is a positive integer, r k (n k , t) represents the number of times an AVB stream S k is released within the time t, and t takes the value of 1 hour;

[0044] Step 4.3: Calculate the probability of hourly transmission failure pfh”(x) when the AVB stream degrades service through the following formula:

[0045] pfh”(x) ≤ (1 - P(N', t)) × ω(d f , t) (10)

[0046]

[0047] where ω(d f , t) represents the upper limit of the hourly transmission failure probability of the AVB stream; when pfh”(x) < PFH(x), the transmission of the AVB stream is reliable.

[0048] In the real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention, step 5 is specifically as follows:

[0049] Step 5.1: Determine whether the TT stream resources and the AVB stream resources are successfully allocated, and whether the hourly transmission failure probabilities of the TT stream and the AVB stream meet the safety standards;

[0050] Step 5.2: Return success, indicating that the real-time stream in the current network is schedulable and the transmission of the real-time stream is reliable; return failure, indicating that the transmission of the real-time stream in the current network is unreliable or unschedulable, and parameters need to be reset and tested again.

[0051] The real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention, by introducing a probability model of network transmission failures and safety standards for real-time streams of different critical levels, quantifies the number of retransmissions of real-time stream frames, and only retransmits the frames of the real-time stream when instantaneous failures occur, solving the pain point in TSN fault-tolerant scheduling that it is impossible to balance the reliability and schedulability of real-time stream transmission. Compared with the active fault-tolerant scheduling algorithm proposed by Alvarez et al. and the method of transmitting in non-overlapping routes proposed by the IEEE 802.1CB standard, the solution of the present invention not only reduces the network transmission load but also improves the schedulability of real-time stream transmission. On the other hand, by introducing queue isolation and the AVB stream termination or service degradation mechanism, the service quality of the AVB stream is improved, and the transmission reliability of the AVB stream is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a flowchart of the real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0053] As Figure 1 shown, the real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch of the present invention includes:

[0054] Step 1: Input the real-time stream set, network topology, failure rate, safety standards for different critical levels, and time slot length.

[0055] The real-time stream includes: the time-triggered stream (Time-Trigger, TT), i.e., the TT stream, and the audio / video bridging stream (AudioVideo Bridging, AVB), i.e., the AVB stream. The critical level of the TT stream is higher than that of the AVB stream.

[0056] Network topology: The switches in the network topology need to support the functions of cyclic redundancy check and automatic repeat request.

[0057] Failure rate: It refers to the frequency at which a frame fails to be transmitted in a link, and the exponential distribution is used to represent the probability of instantaneous failure during the transmission of the real-time stream. Since the exponential distribution can be used to describe the time intervals between failures of large and complex systems such as computers.

[0058] Safety standards for different critical levels: To describe the reliability of network transmission, the probability-of-failure-per-hour (PFH) is introduced as a safety standard indicator. PFH is adopted by most safety and reliability standards, such as the DO-178B standard (Authority, F.A., 1992. Software considerations in airborne systems and equipment certification. Document No. RTCA / DO-178B). The values of the PFH indicators satisfied by real-time streams with different critical levels are different, and as the critical level of the real-time stream increases, the value of PFH will become smaller and smaller.

[0059] This patent uses the DO-178B standard to measure the reliability of real-time stream transmission. The DO-178B standard includes 5 critical levels: A, B, C, D, and E. Their PFH requirements are respectively PFH(A) < 10 -9 、PFH(B) < 10 -7 、PFH(C) < 10 -5 、PFH(C) ≥ 10 -5 , E has no requirement. Among them, D and E do not belong to the category of real-time streams because the probability of error is too high. Therefore, 3 critical levels A, B, and C in the DO-178B standard are used to measure the reliability of real-time stream transmission. Among them, the TT stream belongs to levels A and B, and there are distinctions in the attributes of the TT stream. The AVB stream only belongs to level C, and the symbols x are used to represent A, B, or C.

[0060] Slot length: The IEEE 802.1Qch standard divides the transmission period of the real-time stream into equal-length slots, and requires the real-time stream to be transmitted to the next node within the slot. The length of the slot is set by the user.

[0061] Step 2: Calculate the minimum number of redundant copies of frames for real-time streams of different critical levels when meeting the safety standards. Specifically, Step 2 is as follows:

[0062] Step 2.1: Calculate the probability of hourly transmission failure for TT streams or AVB streams according to formula (1):

[0063]

[0064] where, pfh(x) represents the probability of hourly transmission failure for the set S of real-time streams with critical level x; x represents critical levels A, B, or C; x the probability of hourly transmission failure; x indicates critical levels A, B, or C; represents the probability that all frames of a real-time stream S i are transmitted unsuccessfully in a route; represents the probability that all n i frame copies of a real-time stream S i are all transmitted unsuccessfully in a route; r i (n i , t) represents the number of releases of a real-time stream S i within time t, where t takes the value of 1 hour;

[0065]

[0066] where, represents the probability that the j-th frame of a real-time stream S i is transmitted unsuccessfully on the link [v a , v b , and its value range is [0, 1]; is the probability that the j-th frame of the real-time stream S i is transmitted successfully on the link [v a , v b ; is the probability that a frame is transmitted successfully simultaneously in a route R i ; is the probability that all frames of the real-time stream S i are transmitted successfully simultaneously in a route, NF i is the number of frames in a real-time stream S i ; where a real-time stream S i can contain one or more frames, which is determined by the length of the stream and the device fragmentation strategy; a route contains multiple links;

[0067]

[0068] where, λ is the failure rate, which is set by the user according to the working scenario of the device; is the time for a frame to be transmitted on this link, which is determined by the length of the frame and the parameters of the port; e is the natural constant;

[0069]

[0070] Among them, C i represents the total transmission duration of the real-time stream S i , that is, the sum of the transmission times of all links; n i represents the number of copies of the frames of the real-time stream S i released once, that is, n i ×C i represents the total transmission duration of the n i frame copies of the real-time stream S i ; T i is the period of the real-time stream S i ;

[0071] Step 2.2: Introduce the maximum probability of transmission failure of all frames of a real-time stream S i in a route and the maximum probability of transmission failure per hour of the set S of real-time streams with a critical level of x to calculate the minimum number of redundant copies of the frames of real-time streams at each critical level: x If pfh(x) has an upper limit and the upper limit meets the corresponding reliability requirements, then the transmission of the real-time stream at this level is reliable. Introduce the following formula:

[0072]

[0073]

[0074] Among them, represents the maximum value of the probability of transmission failure of the j-th frame of the real-time stream S i in a route, that is, the maximum value of formula (3); is determined by the parameter λ and the transmission time of the real-time stream in a link, that is, when λ is the largest and the transmission time in a link is the longest, it is the maximum value, and the link with the longest transmission time is denoted as When reaches the maximum value, the transmission time of each link needs to be the maximum value. Then, each link at this time is represents the number of such links in this route;

[0075]

[0076] When , that is, the theoretical maximum value of the probability of real-time stream transmission failure meets the reliability requirements, and the actual probability of real-time stream transmission failure will not be greater than​ Therefore, the transmission of all real-time streams at this level is reliable; in PFH(x), x represents the critical levels A, B, or C; for the convenience of calculation, it is stipulated that real-time streams at the same level have the same number of redundant copies, that is, when x is the same, n i is the same. At this time, it can be derived from the minimum number of copies n of the frames of the real-time stream, that is, the minimum number of redundant copies. i

[0077] Step 3: Calculate the duration required for the transmission of a TT stream or an AVB stream based on the minimum number of redundant copies of the frames calculated in Step 2, and allocate network resources for the TT stream and the AVB stream according to the rule that the TT stream and the AVB stream are stored in different queues and the TT stream is preferentially transmitted;

[0078] Specifically, in a time slot of the transmission, the high-criticality stream, that is, the TT stream, is preferentially transmitted, and the remaining time is used to transmit the AVB stream. During the transmission process, retransmission is only performed if an error occurs. The present invention adopts the MSS scheduling algorithm to offline allocate network resources for the TT stream, including the transmission time slot and port queue of the stream (Guo M, Gu C, He S, et al. MSS: Exploiting Mapping Score for CQF Start Time Planning in Time-Sensitive Networking[J]. IEEE Transactions on Industrial Informatics, 2022, 19(2): 2140-2150.). The Credit Based Shaper (CBS) is used to schedule the AVB stream (Maxim D, Song Y Q. Delay analysis of AVB traffic in time-sensitive networks (TSN)[C] / / Proceedings of the 25th International Conference on Real-Time Networks and Systems. 2017: 18-27.).

[0079] Step 4: Schedule the TT stream and the AVB stream based on the network resources allocated in Step 3, and then calculate the probability of hourly transmission failure of the TT stream and the AVB stream during actual transmission. Step 4 includes:

[0080] Step 4.1: Calculate the probability of hourly transmission failure of the TT stream and the AVB stream during actual transmission according to formula (1);

[0081] ​Step 4.2: When the AVB stream cannot be transmitted before its deadline, the AVB stream needs to be terminated or service degraded. Calculate the probability of transmission failure per hour pfh'(x) when the AVB stream is terminated by the following formula:

[0082]

[0083] where P(N',α) represents the minimum probability that all TT streams are successfully transmitted for the first n i copies within the time interval [0,α]; represents the maximum probability of transmission failure of all frames of an AVB stream S k in a single route; n k represents the number of copies of the frames of an AVB stream S k released once; when pfh'(x) < PFH(x), the transmission of the AVB stream is reliable;

[0084]

[0085] P(N',t) represents the minimum probability that all TT streams are successfully transmitted for the first n i - 1 copies within the time interval [0,t], and at this time, the transmission of the AVB stream will not be affected by the TT stream; then the upper limit of the probability that the AVB stream is terminated or service degraded is 1 - P(N',t);

[0086]

[0087] where, P k (t) represents the set of the latest completion times of the frames released each time by an AVB stream S k within the time interval [0,t]; C k represents the total transmission duration of the AVB stream S k , T k and D k are the period and deadline of the AVB stream S k respectively; is a positive integer, r k (n k ,t) represents the number of times an AVB stream S k is released within the time t, and t takes the value of 1 hour;

[0088] Step 4.3: Calculate the probability of transmission failure per hour pfh”(x) when the AVB stream is service degraded by the following formula:

[0089] pfh”(x) ≤ (1 - P(N',t)) × ω(d f ,t) (10)

[0090]

[0091] where ω(d f , t) represents the upper limit of the hourly transmission failure probability of the AVB stream; when pfh”(x) < PFH(x), the transmission of the AVB stream is reliable.

[0092] Step 5: Determine whether the hourly transmission failure probabilities of the TT stream and the AVB stream meet the safety standards. If both are yes, return success; otherwise, return failure. The specific steps of Step 5 are as follows:

[0093] Step 5.1: Determine whether the resources of the TT stream and the AVB stream are successfully allocated, and whether the hourly transmission failure probabilities of the TT stream and the AVB stream meet the safety standards;

[0094] Step 5.2: Return success, indicating that the real-time streams in the current network are schedulable and the transmission of the real-time streams is reliable; return failure, indicating that the transmission of the real-time streams in the current network is unreliable or unschedulable, and parameters need to be reset and tested again.

[0095] The present invention proposes a real-time stream instantaneous fault tolerance scheduling method for IEEE 802.1Qch. When an instantaneous fault occurs in the real-time stream transmission, retransmission is performed, and this passive retransmission method saves network resources and improves the schedulability of the real-time stream. Moreover, a queue isolation mechanism is introduced to solve the problem that the AVB stream affects the transmission of the TT stream. In addition, when the AVB stream cannot be transmitted, the AVB stream is terminated or service degraded to meet the requirements of transmission reliability.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the idea of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch, characterized in that, Including: Step 1: Input a set of real-time streams, network topology, failure rate, safety criteria for different critical levels, and time slot length. The real-time streams include TT streams and AVB streams, and the critical level of TT streams is higher than that of AVB streams; Step 2: Calculate the minimum number of redundant copies of frames for real-time streams with different critical levels when meeting the safety criteria; Step 3: Based on the minimum number of redundant copies of frames calculated in Step 2, calculate the transmission duration required for a TT stream or an AVB stream. According to the rule that TT streams and AVB streams are stored in different queues and TT streams are preferentially transmitted, allocate network resources for TT streams and AVB streams; Step 4: Schedule TT streams and AVB streams using the network resources allocated in Step 3, and then calculate the probability of hourly transmission failures for TT streams and AVB streams during actual transmission; Step 5: Determine whether the probability of hourly transmission failures for TT streams and AVB streams meets the safety criteria. If both are yes, return success; otherwise, return failure.

2. The real-time flow instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 1, wherein The safety criteria for different critical levels are specifically: To describe the reliability of network transmission, the probability of failure per hour (PFH) is introduced as a safety standard metric. The three critical levels A, B, and C in the DO-178B standard are used to measure the reliability of real-time stream transmission. The PFH requirements for the three critical levels are PFH(A) < 10 -9 , PFH(B) < 10 -7 , and PFH(C) < 10 -5 ; The TT stream belongs to level A or B, and the AVB stream belongs to level C.

3. The real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 1, wherein, The switches in the network topology support the functions of cyclic redundancy check and automatic repeat request.

4. The real-time flow instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 1, characterized in that, The failure rate refers to the frequency of a frame transmission failure in a link, and the exponential distribution is used to represent the probability of instantaneous failures occurring during the transmission of real-time streams.

5. The real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 2, characterized in that, The specific content of Step 2 is: Step 2.1: Calculate the probability of hourly transmission failures for a TT stream or an AVB stream according to formula (1): Among them, pfh(x) represents the set S of real-time streams with a critical level of x x The probability of transmission failure per hour; x represents the critical levels A, B, or C; Represents a real-time stream S i The probability that all frames of i (n i ,t) represents a real-time stream S i The number of releases within time t, where t takes the value of 1 hour; wherein, represents the j-th frame of a real-time stream S i transmitted over the link [v a , v b with a failure probability, whose value range is [0, 1], and NF i is the number of frames in a real-time stream S i ; Among them, λ is the failure rate, which is set by the user according to the working scenario of the device; is the time for the frame to be transmitted on this link, which is determined by the length of the frame and the parameters of the port; e is the natural constant; Among them, C i represents the total transmission duration of the real-time stream S i , that is, the sum of the transmission times of all links; n i represents the number of copies of the frames of the real-time stream S i released once; T i is the period of the real-time stream S i . Step 2.2: Introduce a real-time stream S i The maximum probability that all frames of are transmitted unsuccessfully in one route, and the set S of real-time streams with critical level x x The maximum probability of transmission failure per hour Calculate the minimum number of redundant copies of real-time stream frames for each critical level: If pfh(x) has an upper limit and the upper limit meets the corresponding reliability requirements, then the transmission of real-time streams at this level is reliable. Introduce the following formula: Among them, represents the maximum probability of transmission failure of the j-th frame of the real-time stream S i in a route, that is, the maximum value of Equation (3); It is determined by the parameter λ and the transmission time of the real-time stream in a link, that is, when λ is the largest and the transmission time in a link is the longest, it is the maximum value, and the link with the longest transmission time is denoted as When reaches the maximum value, the transmission time of each link needs to be the maximum value. At this time, each link is represents the number of such links in this route; When the theoretical maximum value of the probability of real-time stream transmission failure meets the reliability requirements, and the probability of actual transmission failure of the real-time stream will not be greater than Therefore, the transmission of all real-time streams at this level is reliable; in PFH(x), x represents the critical levels A, B, or C; for the convenience of calculation, it is stipulated that real-time streams of the same level have the same number of redundant copies, that is, when x is the same, n i is the same; at this time, the minimum value of the number of copies n of the frames of the real-time stream can be derived from i that is, the minimum number of redundant copies.

6. The real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 5, characterized in that, The specific content of Step 4 includes: Step 4.1: Calculate the probability of hourly transmission failures for TT streams and AVB streams during actual transmission according to formula (1); Step 4.2: When an AVB stream cannot complete transmission before its deadline, terminate or degrade the service of the AVB stream. Calculate the probability of hourly transmission failures pfh'(x) when the AVB stream is terminated through the following formula: Among them, P(N', α) represents the minimum probability that all TT flows are successfully transmitted for the first n i copies within the time interval [0, α]; represents the maximum probability that all frames of an AVB flow S k are transmitted with failures in a route; n k represents the number of copies of the frames of an AVB flow S k released once; when pfh'(x) < PFH(x), the transmission of the AVB flow is reliable; P(N',t) represents the minimum probability that all TT flows have the first n - 1 copies successfully transmitted within the time interval [0, t], where the transmission of the AVB flow is not affected by the TT flow; i ​ Among them, P k (t) represents the set of the latest completion transmission times of each frame released in the AVB stream S k in the time interval [0, t]; C k represents the total transmission duration of the AVB stream S k , T k and D k are the period and deadline of the AVB stream S k respectively; is a positive integer, r k (n k , t) represents the number of times an AVB stream S k is released within the time t, and t takes the value of 1 hour; Step 4.3: Calculate the probability of hourly transmission failures pfh”(x) when the AVB stream's service is degraded through the following formula: pfh”(x)≤(1 - P(N', t)) × ω(d f , t) (10) where ω(d f , t) represents the upper limit of the hourly transmission failure probability of the AVB stream; when pfh”(x) < PFH(x), the transmission of the AVB stream is reliable.

7. The real-time stream instantaneous fault-tolerant scheduling method for IEEE 802.1Qch according to claim 1, wherein The specific content of Step 5 is: Step 5.1: Determine whether the allocation of TT stream resources and AVB stream resources is successful, and whether the probability of hourly transmission failures for TT streams and AVB streams meets the safety criteria; Step 5.2: Return success, indicating that the real-time streams in the current network are schedulable and the transmission of real-time streams is reliable; Return failure, indicating that the transmission of real-time streams in the current network is unreliable or unschedulable, and parameters need to be reset and tested again.

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