Fault analysis method for communication system based on FTA and FMEA

Abstract

The invention discloses a communication system fault analysis method based on FTA and FMEA, and the method comprises the following steps: building an MBSE model of a communication system based on an MBSE methodology, and taking the MBSE model as a model basis of system fault analysis; based on the MBSE model of the system, establishing a function fault tree by adopting an FTA method, identifying a hierarchical relationship between system function blocks, and performing fault analysis; based on the function fault tree, using an FMEA method to analyze important function blocks of each level, and generating an FMEA analysis table corresponding to each level; and integrating the function fault tree and the FMEA analysis table of each level function block, establishing a function fault database of the communication system, and finally generating a fault analysis report of the system. Through systematic design and hierarchical analysis, the fault cause of the system can be comprehensively identified and analyzed, the fault analysis efficiency is improved, and the reliability and performance of the system are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of communication systems, relates to communication system fault analysis, and specifically relates to a communication system fault analysis method based on FTA and FMEA. Background Art

[0002] As the core of modern information transmission, communication systems play a vital role in all walks of life. In recent years, with the rapid development of technology and the continuous growth of demand, the scale and complexity of communication systems have increased significantly. As a large and complex system, traditional fault analysis methods are often unable to cope with such complex systems. Not only does it consume a lot of manpower, financial resources and time, but it is also difficult to guarantee the comprehensiveness and accuracy of the analysis results. Summary of the invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, a communication system fault analysis method based on FTA and FMEA is provided, which systematically designs and analyzes the faults of the communication system by combining the MBSE (model-based system engineering) method, fault tree analysis (FTA) and failure mode and effect analysis (FMEA) method. By establishing a detailed MBSE model, the potential faults at all levels of the system are systematically identified and analyzed, a fault risk library is formed, and a fault analysis report is generated, thereby improving the efficiency of fault analysis, quickly identifying fault modes and causes, finding effective fault resolution measures, and significantly improving the reliability and performance of the system.

[0004] Technical solution: To achieve the above purpose, the present invention provides a communication system fault analysis method based on FTA and FMEA, comprising the following steps:

[0005] S1: Based on MBSE methodology, establish the MBSE model of the communication system as the model basis for system fault analysis;

[0006] S2: Based on the MBSE model of the system, the FTA method is used to establish a functional fault tree, identify the hierarchical relationship between system functional blocks and perform fault analysis;

[0007] S3: Based on the functional fault tree, use the FMEA method to analyze the important functional blocks at each level and generate the corresponding FMEA analysis tables at each level;

[0008] S4: Integrate the functional fault tree and FMEA analysis tables of functional blocks at each level, establish a functional fault database of the communication system, and finally generate a system fault analysis report.

[0009] Furthermore, the method for establishing the MBSE model of the communication system in step S1 is: using the MBSE method to model the system, dividing the modeling into three levels: logical subsystem level, component level and interface level, modeling the communication system from top to bottom from the three aspects of system structure, function and parameter, and the logical subsystem level, component level and interface level are respectively used as the first design level, the second design level and the third design level from top to bottom.

[0010] Furthermore, in step S1, the communication system is modeled from top to bottom from the three aspects of system structure, function and parameters, specifically including:

[0011] B1: Model the structure of the communication system. At the logical subsystem level, the system is divided into three logical subsystems: access network, bearer network, and core network. At the component level, these logical subsystems are further decomposed into specific network elements. At the interface level, interfaces are added to components and divided into several protocol layers so that each component can communicate through the interface in a prescribed manner.

[0012] B2: Model the functions of the communication system. At the logical subsystem level, an activity diagram of the connected mobility management function is established, covering the measurement reporting, terminal location reporting, intra-frequency switching and inter-frequency switching functional blocks. At the component level, taking the measurement reporting functional block as an example, a sequence diagram of measurement reporting is established. At the interface level, taking the Uu-C interface sending data on the UE side as an example, an activity diagram of the interface sending data is established.

[0013] B3: Model the parameters of the communication system. Several service indicators of the system are decomposed layer by layer from top to bottom, through the logical subsystem level, component level and interface level, and finally implemented as service indicators of the protocol layer.

[0014] Furthermore, the method for establishing the functional fault tree in step S2 is specifically as follows: selecting the logical subsystem level functional blocks in the MBSE model as fault analysis objects, and establishing the functional fault tree.

[0015] Furthermore, the step S3 specifically includes:

[0016] A1: Based on the functional fault tree and the MBSE model of the system, the connected mobility management functional block is taken as the analysis object, and the FMEA analysis method is used to perform FMEA analysis on the functional blocks of the first design level (logical subsystem level) to form an FMEA analysis table;

[0017] A2: After completing the FMEA analysis at the logical subsystem level, take the measurement reporting function block as the analysis object, combine the functional fault tree, MBSE model and the FMEA analysis results at the logical subsystem level, use the FMEA analysis method, and perform FMEA analysis on the function blocks at the second design level (component level) to form the corresponding FMEA analysis table;

[0018] A3: Following the component-level analysis, based on the functional fault tree, MBSE model and component-level FMEA analysis results, the Uu-C interface (UE side) data sending function block is taken as the analysis object, and the FMEA analysis method is used to perform FMEA analysis on the function blocks of the third design level (interface level) to form a corresponding FMEA analysis table.

[0019] Furthermore, in the FMEA analysis table of step A1, the FMEA items include FMEA ID, FMEA name, current level behavior, failure mode, failure cause, next level behavior, upper level failure impact, previous level behavior, final failure impact, OCC (failure frequency), SEV (failure impact severity) and design improvement measures.

[0020] Furthermore, in the FMEA analysis table of step A2, the FMEA items include FMEA ID, FMEA name, current level behavior, network element, physical entity, failure mode, failure cause, next level behavior, interface, upper level failure impact, previous level behavior, final failure impact, OCC (failure frequency), SEV (failure impact severity) and design improvement measures.

[0021] Furthermore, in the FMEA analysis table of step A3, the FMEA items include FMEA ID, FMEA name, current level behavior, interface, physical entity, failure mode, failure cause, next level behavior, protocol layer specific behavior, protocol layer index, upper level failure impact, previous level behavior, final failure impact, OCC (failure frequency), SEV (failure impact severity), and design improvement measures.

[0022] Furthermore, in the step S2, a functional fault tree of connection-state mobility management is established, and the establishment method is: establishing FMEA items of the connection-state mobility management function; the function is decomposed into four functional blocks at the component level: measurement reporting, terminal location reporting, inter-frequency switching and intra-frequency switching; then, the functional blocks at the component level are further decomposed into functional blocks of various interfaces at the interface level, and the functional blocks of the interface are further refined into functional blocks of the protocol layer.

[0023] Fault tree analysis (FTA) is a top-down deductive failure analysis method widely used in the fields of safety engineering and reliability engineering. Through fault tree analysis, we can gain an in-depth understanding of the causes of system failures, find the best risk reduction method, or determine the probability of a safety accident or a specific system failure, thereby enhancing the reliability of the system.

[0024] Failure Mode and Effects Analysis (FMEA) is an analytical method used to identify potential failure modes and their causes. It is widely used to systematically evaluate and reduce the risk of potential failures. FMEA is managed in a table format, including items such as serial number, name, project, failure cause, failure mode, local failure effect, and final failure effect. Among them, the failure mode refers to how the requirements, components or functions fail, which is the core of FMEA analysis. The failure cause leads to the failure mode, and the failure effect is the result of the failure mode.

[0025] The present invention can systematically design and model the communication system through the model-based system engineering (MBSE) method, establish a detailed MBSE model, and provide a solid model foundation for fault analysis. By combining FTA and FMEA to analyze the fault of the communication system, a fault risk library can be established, the efficiency of fault analysis can be improved, the fault mode can be quickly identified, and measures to solve the fault can be found, thereby optimizing the maintenance and management of the system. Through the systematic design of the MBSE model and the efficient fault analysis method of FTA and FMEA, the fault analysis of the communication system is not only more systematic and efficient, but also can significantly improve the reliability and performance of the system, and promote the continuous development of communication technology.

[0026] Beneficial effects: Compared with the prior art, the present invention, through systematic design and modeling, hierarchical fault analysis, combined with FTA and FMEA methods, comprehensively identifies and analyzes the causes of communication system failures, establishes a detailed fault database and generates analysis reports, thereby significantly improving the reliability and performance of the system and enhancing the efficiency of fault management and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process of the present invention.

[0028] Figure 2 Schematic diagram of the MBSE-based communication system modeling method.

[0029] Figure 3 It is a structural diagram of the MBSE model of the communication system.

[0030] Figure 4 Functional diagram of MBSE model for communication system.

[0031] Figure 5 Schematic diagram of the parameters of the MBSE model of the communication system.

[0032] Figure 6 Schematic diagram of a functional fault tree of a connection state mobility management functional block in an embodiment of the present invention.

[0033] Figure 7 The figure shows a FMEA analysis diagram of a connected mobility management functional block in an embodiment of the present invention.

[0034] Figure 8 The diagram is a schematic diagram of the FMEA analysis of the measurement reporting functional block in the embodiment of the present invention.

[0035] Fig. 9 The FMEA analysis diagram of the Uu-C interface (UE) data sending function block in the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0037] like Figure 1 As shown, the present invention provides a communication system fault analysis method based on FTA and FMEA, comprising the following steps:

[0038] S1: Based on the MBSE methodology, establish the MBSE model of the communication system as the model basis for system fault analysis:

[0039] like Figure 2 As shown, the method for establishing the MBSE model of the communication system in step S1 of this embodiment is: using the MBSE method to model the system, dividing it into three modeling levels vertically and three modeling aspects horizontally, specifically dividing the modeling into three levels: logical subsystem level, component level and interface level, modeling the communication system from top to bottom from the three aspects of system structure, function and parameter, and the logical subsystem level, component level and interface level are respectively used as the first design level, the second design level and the third design level from top to bottom.

[0040] like Figure 3As shown in the figure, at the logical subsystem level, the system is divided into three logical subsystems: access network, bearer network, and core network. At the component level, these logical subsystems are further decomposed into specific network elements. For example, the access network is divided into UE (user terminal) and gNB (base station). At the interface level, interfaces are added to components and the interfaces are divided into several protocol layers so that each component can communicate through the interface in a prescribed manner. For example, there is a Uu-C interface on the gNB side, through which the gNB communicates with the UE to transmit control information. The interface contains five protocol layers, namely RRC, PDCP, RLC, MAC, and PHY layers.

[0041] Next, the functions of the communication system are modeled, such as Figure 4 The functional model of the communication system is shown, taking the connected state mobility management function as an example. At the logical subsystem level, an activity diagram of the connected state mobility management function is established, covering the measurement reporting, terminal location reporting, intra-frequency switching and inter-frequency switching functional blocks. At the component level, this embodiment takes the measurement reporting functional block as an example to establish a sequence diagram of measurement reporting. At the interface level, this embodiment takes the Uu-C interface sending data on the UE side as an example to establish an activity diagram of the interface sending data.

[0042] Finally, the parameters of the communication system are modeled, such as Figure 5 The figure shows the parameter model of the MBSE model of the communication system. Several service indicators of the system are decomposed layer by layer from top to bottom, through the logical subsystem level, component level and interface level, and finally implemented as service indicators of the protocol layer.

[0043] S2: Based on the MBSE model of the system, the FTA method is used to establish a functional fault tree, identify the hierarchical relationship between system functional blocks and perform fault analysis:

[0044] This embodiment takes the connected state mobility management functional block as an example. The connected state mobility management ensures that the user equipment can maintain a stable network connection and high-quality service during movement in the connected state by coordinating base station switching, measuring and reporting signal quality, configuring mobility policies, and handling switching failures.

[0045] like Figure 6 The following is the functional fault tree of connected mobility management. First, the FMEA items of connected mobility management function are established, namely Figure 6 The F-29 connection state mobility management in the UE fails. This function is decomposed into four functional blocks at the component level: measurement reporting, terminal location reporting, inter-frequency switching, and intra-frequency switching. Subsequently, the functional blocks at the component level are further decomposed into functional blocks of various interfaces at the interface level, and the functional blocks of the interfaces are further refined into functional blocks of the protocol layer.

[0046] When a connection state mobility management function block fails, it can be traced back through the fault tree. For example, it can be traced back to the failure of the measurement reporting function at the component level, and further traced back to the failure of the interface protocol layer function at the interface level. In this way, the cause of the failure can be analyzed layer by layer to ensure the comprehensiveness and accuracy of the fault analysis.

[0047] S3: Based on the functional fault tree, use the FMEA method to analyze the important functional blocks at each level and generate the corresponding FMEA analysis tables for each level, specifically:

[0048] 1) Based on the functional fault tree and the MBSE model of the system, this embodiment takes the connected mobility management function block as the analysis object, uses the FMEA analysis method, performs FMEA analysis on the function blocks of the first design level (logical subsystem level), and forms an FMEA analysis table;

[0049] This embodiment takes the FMEA item of connection state mobility management failure, i.e., the faulty functional block, as an example for FMEA analysis. Figure 7 The figure shows the FMEA analysis table of the connected mobility management functional block. The FMEA analysis items include the current level behavior, failure mode, failure cause, next level behavior, upper level failure impact, previous level behavior, final failure impact, severity, probability of occurrence, risk index, and design improvement measures. It can be seen that the level behavior of this FMEA item is "connected mobility management". The failure mode is the top-level functional failure. The cause of the failure may be excessive load, configuration error, software problem, network failure, or hardware failure. The next level of functional blocks includes terminal location reporting, measurement reporting, inter-frequency switching, and intra-frequency switching. The upper level failure impact is the inability to perform connected mobility management. The previous level functional block is mobility management. The final failure impact is data transmission interruption or quality degradation. OCC is 1 (failure frequency, the larger the value, the higher the frequency). SEV is 2 (failure impact severity, the higher the value, the higher the impact severity). Design improvement measures include strengthening location management and update, applying fault tolerance and redundancy mechanisms, optimizing network topology, and enhancing signaling coverage and quality.

[0050] The FMEA analysis table for this level of functional blocks provides a comprehensive analysis framework by listing in detail the modes, causes, impacts and control measures of connected mobility management failures, helping to identify and respond to potential system failures.

[0051] 2) After completing the FMEA analysis at the logical subsystem level, this embodiment uses the measurement and reporting function block as the analysis object, combines the functional fault tree, MBSE model and the FMEA analysis results at the logical subsystem level, and uses the FMEA analysis method to perform FMEA analysis on the function block at the second design level (component level) to form a corresponding FMEA analysis table;

[0052] This embodiment takes the measurement reporting function block, the next level function block of connected mobility management, as an example. The function block at the component level is different from the FMEA analysis table at the logical subsystem level because the design refinement of the system structure, function and parameters is different at different design levels. The lower the level, the smaller the design granularity, the more detailed the design, and the more accurate the description of the system. Therefore, compared with the FMEA analysis table at the logical subsystem level, the FMEA analysis table at the component level is more detailed and the fault analysis is more accurate.

[0053] like Figure 8 The figure shows the FMEA analysis table of the measurement reporting function block. According to the FMEA analysis table, the failure mode of the measurement reporting function failure is the network element function failure. The network elements that carry this function block are UE and gNB, and the corresponding physical entities are broadband terminals, ka user loads and integrated processing loads. The failure mode is the network element function failure. The cause of the failure may be a configuration error, software problem, network failure, etc. The function block of the next layer of this function block is the data transmission and reception behavior of several interfaces, and the corresponding interfaces are Uu-C interface (gNB) and Uu-C interface (UE). The impact of the upper-level failure is the failure of network element communication. The function block of the previous layer is the connection state mobility management. The final failure impact is the inability to provide mobility management. OCC is 1 and SEV is 2. The design improvement measures are to increase fault tolerance and redundancy mechanisms, enhance the reliability of the protocol layer, and improve the network environment.

[0054] The FMEA analysis table of this level of functional blocks is detailed and systematic. It shows the functional blocks of different levels of the system through hierarchical decomposition, from network elements to interfaces to physical entities, ensuring the comprehensiveness of fault analysis. It combines system structure and function, accurately locates the source of the fault and traces it back to the specific physical entity. The table provides a comprehensive fault impact analysis and clarifies the design improvement measures for each fault mode, such as adding fault tolerance and redundancy mechanisms, enhancing protocol layer reliability and improving network environment. By evaluating the possibility of failure and the severity of the impact, the table helps identify high-risk areas, prioritizes them, and improves the reliability and stability of the system.

[0055] 3) Following the component-level analysis, based on the functional fault tree, MBSE model and component-level FMEA analysis results, the Uu-C interface (UE side) data sending function block is taken as the analysis object, and the FMEA analysis method is used to perform FMEA analysis on the function blocks of the third design level (interface level) to form the corresponding FMEA analysis table:

[0056] This embodiment takes the Uu-C interface (UE side) data sending function block, the next level function block of the measurement report, as an example. The FMEA analysis items of the interface-level function blocks and the component-level function blocks are different. The interface level is the lowest level of the design level, with the highest degree of design sophistication. The description of the system parameters is more detailed and accurate, and the system service indicators are placed on the specific indicators of the protocol layer that can be measured and calculated. The component-level FMEA analysis table adds specific indicators of the protocol layer on the basis of adding system structure information to facilitate parameter analysis of faults.

[0057] like Fig. 9 The figure shows the FMEA analysis table of the Uu-C interface (UE side) data transmission function block. According to the FMEA analysis table, the interface carried by this function block is the Uu-C interface (UE), and the corresponding physical entity is the broadband terminal. The failure mode is interface failure, and the cause of the failure may be a destination address error, a configuration error, a software problem, or a hardware failure. The function block at the next level is the behavior of receiving and sending data at several protocol layers of the interface. The protocol layer receiving and sending data can be decomposed into specific protocol layer function blocks. The interface function block contains specific indicators of the protocol layer, such as the receiver algorithm of PHY, the communication system of PHY, and the delay of sending and receiving data at the RRC layer. By analyzing these specific protocol layer indicators, the fault can be more accurately located so as to quickly resolve the fault. The impact of the upper-level fault is interface communication failure. The function blocks at the previous level include PDU session establishment, release, modification, connection establishment, etc. The final fault impact is the failure of the network element function, OCC is 3, and SEV is 4. The design improvement measures are software optimization, protocol layer improvement, etc.

[0058] The advantage of the FMEA analysis table of the functional block at this level lies in its detailedness and accuracy. By refining the fault analysis to the interface level, the service indicators and parameters of the system are clarified, and the fault location is more accurate. The table not only adds system structure information, but also adds specific indicators of the protocol layer, which facilitates parameterized analysis of faults. By analyzing specific indicators such as the PHY receiver algorithm, PHY communication system, and RRC layer data transmission and reception delay, once the functional fault is defined to a specific indicator, more accurate fault resolution measures can be proposed. The correlation analysis of the upper and lower levels further enhances the comprehensiveness and systematicness of the fault analysis. Risk assessment indicators (OCC, SEV) and design improvement measures (such as software optimization, protocol layer improvement) provide clear guidance for system maintenance and optimization, which helps to improve the reliability and performance of the system.

[0059] S4: Comprehensive functional fault tree and FMEA analysis tables of functional blocks at each level, establish the functional fault database of the communication system, and finally generate the system fault analysis report:

[0060] FMEA analysis is performed on all important functional blocks at the three design levels. After the FMEA table is formed, a functional fault library is established in combination with the functional fault tree; based on the MBSE model, a communication system fault library is constructed and a fault analysis report is generated. This step ensures that the functional blocks at each level are analyzed and recorded in detail, forming a comprehensive fault management database, providing a solid foundation for system maintenance and optimization.

Claims

1. A communication system fault analysis method based on FTA and FMEA, characterized in that: The steps include: S1: Based on MBSE methodology, establish the MBSE model of the communication system as the model basis for system fault analysis; S2: Based on the MBSE model of the system, the FTA method is used to establish a functional fault tree, identify the hierarchical relationship between system functional blocks and perform fault analysis; S3: Based on the functional fault tree, use the FMEA method to analyze the important functional blocks at each level and generate the corresponding FMEA analysis tables at each level; S4: Integrate the functional fault tree and FMEA analysis tables of functional blocks at each level, establish a functional fault database of the communication system, and finally generate a system fault analysis report.

2. The communication system fault analysis method based on FTA and FMEA according to claim 1, characterized in that: The method for establishing the MBSE model of the communication system in step S1 is: using the MBSE method to model the system, dividing the modeling into three levels: logical subsystem level, component level and interface level, modeling the communication system from top to bottom from the three aspects of system structure, function and parameter, and the logical subsystem level, component level and interface level are respectively used as the first design level, the second design level and the third design level from top to bottom.

3. The communication system fault analysis method based on FTA and FMEA according to claim 2 is characterized in that: The method for establishing the functional fault tree in step S2 is specifically as follows: selecting the logical subsystem level functional blocks in the MBSE model as fault analysis objects, and establishing the functional fault tree.

4. The communication system fault analysis method based on FTA and FMEA according to claim 2, characterized in that: The step S3 specifically includes: A1: Based on the functional fault tree and the MBSE model of the system, the connected mobility management functional block is taken as the analysis object, and the FMEA analysis method is used to perform FMEA analysis on the functional blocks of the first design level to form an FMEA analysis table; A2: Taking the measurement reporting function block as the analysis object, combining the FMEA analysis results of the functional fault tree, MBSE model and logical subsystem level, using the FMEA analysis method, conduct FMEA analysis on the function block of the second design level to form the corresponding FMEA analysis table; A3: Based on the FMEA analysis results of the functional fault tree, MBSE model and component level, the Uu-C interface data sending function block is taken as the analysis object, and the FMEA analysis method is used to perform FMEA analysis on the function blocks of the third design level to form the corresponding FMEA analysis table.

5. The communication system fault analysis method based on FTA and FMEA according to claim 4 is characterized in that: In the FMEA analysis table of step A1, the FMEA items include FMEA ID, FMEA name, current level behavior, failure mode, failure cause, next level behavior, upper level failure impact, previous level behavior, final failure impact, OCC, SEV and design improvement measures.

6. The communication system fault analysis method based on FTA and FMEA according to claim 4, characterized in that: In the FMEA analysis table of step A2, the FMEA items include FMEA ID, FMEA name, current level behavior, network element, physical entity, failure mode, failure cause, next level behavior, interface, upper level failure impact, previous level behavior, final failure impact, OCC, SEV and design improvement measures.

7. The communication system fault analysis method based on FTA and FMEA according to claim 4 is characterized in that: In the FMEA analysis table of step A3, the FMEA items include FMEA ID, FMEA name, current level behavior, interface, physical entity, failure mode, failure cause, next level behavior, protocol layer specific behavior, protocol layer index, upper level failure impact, upper level behavior, final failure impact, OCC, SEV, and design improvement measures.

8. The communication system fault analysis method based on FTA and FMEA according to claim 3 is characterized in that: In the step S2, a functional fault tree for connection-state mobility management is established, and the establishment method is: establishing FMEA items for connection-state mobility management function; the function is decomposed into four functional blocks at the component level: measurement reporting, terminal location reporting, inter-frequency switching and intra-frequency switching; then, the functional blocks at the component level are further decomposed into functional blocks of various interfaces at the interface level, and the functional blocks of the interface are further refined into functional blocks of the protocol layer.

9. The communication system fault analysis method based on FTA and FMEA according to claim 2, characterized in that: In step S1, the communication system is modeled from top to bottom from the three aspects of system structure, function and parameters, specifically including: B1: Model the structure of the communication system. At the logical subsystem level, the system is divided into three logical subsystems: access network, bearer network, and core network. At the component level, these logical subsystems are further decomposed into specific network elements. At the interface level, interfaces are added to components and divided into several protocol layers so that each component can communicate through the interface in a prescribed manner. B2: Model the functions of the communication system. At the logical subsystem level, an activity diagram of the connected mobility management function is established, covering the measurement reporting, terminal location reporting, intra-frequency switching and inter-frequency switching functional blocks. At the component level, taking the measurement reporting functional block as an example, a sequence diagram of measurement reporting is established. At the interface level, taking the Uu-C interface sending data on the UE side as an example, an activity diagram of the interface sending data is established. B3: Model the parameters of the communication system. Several service indicators of the system are decomposed layer by layer from top to bottom, through the logical subsystem level, component level and interface level, and finally implemented as service indicators of the protocol layer.

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