Abstract: This paper delves into the virtual instrument network testing technology based on switched Ethernet, analyzes switched Ethernet and its network testing system in detail, and elaborates on the implementation of the system's network functions. Keywords: Switched Ethernet; Virtual Instrument; Network Testing; DataSocket 0 Introduction With the rapid development of science and technology and the significant improvements in the performance of systems such as data communication, network engineering, and information management, an opportunity has arisen to combine automatic testing technology, computer technology, and communication technology. Using network technology to connect test devices scattered in different locations with different functions allows expensive hardware and software to be shared within the network, thereby reducing redundant investment in equipment, lowering the cost of the testing system, enabling remote diagnosis and maintenance of test equipment, and achieving remote measurement and control and resource sharing. 1 Switched Ethernet Technology for Virtual Instrument Network Testing Systems Real-time control and its deterministic implementation are important indicators of networked testing tasks and are also a type of network technology. The application of Ethernet has brought new hope to networked testing; its performance, speed, and quality of information transmission are unmatched by other fieldbus systems. 1.1 Introduction to Ethernet Technology Ethernet technology is currently the most widely used computer network technology. The Ethernet system was first created by Xerox, and it uses a carrier multiple listener/collision detection mechanism to resolve media collisions. In this method, all workstations share a single network cable, but only one workstation can use the cable at any given time. An Ethernet adapter only transmits information packets over the shared network when it has exclusive access to the cable. Collision detection is used to resolve simultaneous access to the cable. When the cable is idle, two or more stations may attempt to access it simultaneously. If they transmit information at the same time, the information sent by these stations will collide, resulting in data corruption. Ethernet uses the IEEE 802.3 standard and employs the CSMA/CD protocol to resolve media access collisions. Using the CSMA/CD protocol, when the detection mechanism detects a collision, the workstation stops transmitting and retransmits within an arbitrarily long time interval. The retransmission time is a random time slice between 0 and -1, where i represents the i-th collision event, and the time slice length refers to the shortest time required for a round trip. The CSMA/CD mechanism effectively reduces network congestion and transmission collisions. The application of bridges and hubs allows for arbitrary expansion of the network structure, while dividing the network into independent collision domains, improving network quality and further enhancing performance. The CSMA/CD method is very effective when the network load is light, but more collisions will occur as the traffic increases. The CSMA/CD mechanism has raised concerns about determinism, especially in real-time testing, control, and data acquisition. 1.2 Switched Ethernet As is well known, Ethernet systems used in the past were all shared Ethernet systems. However, the number of workstations on local area networks has increased significantly, and a large amount of data needs to be transmitted over the network, requiring a higher data transmission rate. However, shared Ethernet is constrained by the CSMA/CD media access control method, where each station competes for and shares network bandwidth, thus placing the entire network system within a collision domain. Within a collision domain, the more stations there are, the less bandwidth each station receives, meaning less data is sent to the medium per second. In this situation, a switched Ethernet system has emerged. The evolution from shared Ethernet to switched Ethernet represents a significant leap in LAN technology, primarily due to the resolution of bandwidth issues, resulting in a tenfold or even hundredfold increase in system bandwidth. Switched Ethernet utilizes a switching hub as the core device to connect stations or network segments, as shown in Figure 1. The main characteristic of a switching hub is that all ports are normally disconnected. When a workstation needs to transmit information, the hub can simultaneously connect multiple ports, allowing each workstation communicating between ports to transmit data conflict-free, as if it had exclusive access to the communication medium. Once communication is complete, the connection is closed. Therefore, the input and output of frames between ports are no longer constrained by the CSMA/CD media access control protocol. If the original Ethernet transmission rate was 100 Mb/s, using a switching hub, although the data transmission rate remains unchanged, means that each user has exclusive access to the transmission medium's bandwidth, rather than sharing it with other users. Therefore, for a switching hub with N pairs of ports, its total capacity becomes N × 100 Mb/s. It is evident that expanding the overall system bandwidth is the biggest characteristic of switched Ethernet. [align=center] Figure 1 Ethernet Hub[/align] 1.3 Advantages of Switched Ethernet Technology Ethernet is a very economical and efficient network that can meet the requirements of most networked testing. Its complete openness and wide application are unmatched by any fieldbus at present. The newly developed switched Ethernet is more superior than the previous shared Ethernet. It has all the advantages of traditional Ethernet, such as: low cost, high communication rate, complete openness, ability to meet the requirements of various levels of control system, strong anti-interference ability, etc., and also has the following advantages: (1) The maximum bandwidth of the system can reach n times the port bandwidth (where n is the number of ports). That is, the more ports there are, the wider the bandwidth that the system can achieve. (2) Each port can connect to a station or network segment, which each has its own 10M or 100M bandwidth. (3) The information flow on the independent network segment isolated by the switch will not be propagated to other ports, which has a certain degree of data security. (4) The multiple network segments connected by the switch are independent and isolated from each other. The operation of one network segment will not affect the operation of other network segments. 2 Composition of Virtual Instrument Network Testing System A virtual instrument is a new type of instrument that uses an existing personal computer, equipped with appropriate instrument hardware, and with the help of computer-specific software to realize the measurement functions of a general instrument. It has special functions that general instruments do not have. It utilizes the powerful computing power of the computer system and, through hardware cooperation, greatly breaks through the limitations of traditional instruments in data processing, display, transmission, etc., so that users can easily maintain, expand and upgrade it. In the testing system, it is often necessary to centrally control multiple instruments and equipment and perform unified analysis and processing on their data. A large and complex data acquisition, result analysis and processing is often distributed in different geographical locations, which requires several computers distributed in different geographical locations to complete the entire testing task together. In this case, networked testing becomes a very effective method. The networked testing system is physically distributed on two or more computers, and each computer works collaboratively or runs in parallel to complete a testing task. Therefore, it can be viewed as a physically distributed, network-based, and dynamically receiving and executing given tasks complete testing system. A virtual instrument networked testing system generally consists of two main parts: one is the communication part, i.e., the communication network; the other is the basic functional units, consisting of network-enabled PCs, virtual instruments, and servers connected by the communication network. The underlying testing layer uses virtual instruments, fully leveraging their strong programmability and powerful functions to achieve testing of complex systems. The test server and data server connect the virtual instrument devices and the central management computer via Ethernet, forming a scalable networked testing system. Therefore, the composition of an Ethernet-based virtual instrument network testing system is shown in Figure 2. [align=center] Figure 2: Structure Diagram of a Virtual Instrument Network Testing System[/align] This system can achieve interconnection of a large number of test instruments, simultaneous operation of a large number of instruments, and high-speed transmission and exchange of large amounts of data. Therefore, it can be used for testing large and complex systems where a large number of test instruments are distributed, remotely automated, and test information needs to be exchanged. If the testing scope needs to be expanded, multiple testing systems can be interconnected through routers or internet interfaces. This allows the measurement scope to be expanded to all parts of the country, or even the world, enabling measurement and information exchange at the same measurement point. 3. DataSocket – Implementation of System Network Functions DataSocket is a network measurement and control system development tool provided by NI, which allows data to be shared between different applications and data sources. DataSocket uses an enhanced data type to exchange instrument-type data, including data characteristics and actual test data. Although there are various technologies such as TCP/IP and DDE for sharing data between two applications, these technologies are not for real-time data (Live Data) transmission. Only DataSocket is a technology for sharing and publishing real-time data in measurement and automation applications. Utilizing a client/server architecture, data transmission over the network is optimized, and it becomes possible for users to interactively transmit field data over the network, as shown in Figure 3. [align=center] Figure 3 DataSocket Architecture[/align] DataSocket follows the TCP/IP protocol and provides a high degree of encapsulation at the underlying level. The parameters provided are simple and user-friendly; only a Universal Resource Locator (URL) is needed to promptly distribute the required data over the network. DataSocket represents various types of data in its own unique encoding format, including strings, numbers, Booleans, and waveforms. It can also establish connections between field data and user-defined attributes. Based on communication requirements, LabVIEW provides the following three tools: (1) DataSocket ActiveX The DataSocket ActiveX control is used to connect data sources and data sinks and enable them to share data. It can be used to develop shared data applications in the ActiveX environment. (2) DS Server The DataSocket Server is a small, stand-alone program. To transmit data using DS technology, both the server and the client must open the DataSocket Server. It is feasible to communicate and exchange data between two applications using the DSTP protocol. The program that publishes data outputs data through it, and the program that inputs data finds it to receive data. (3) DataSocket Server Manager The DataSocket Server Manager is also a small, stand-alone program. Its main functions are to set the number of clients that can connect to the DS Server and the number of data items that can be created, set user permissions, and predefine data items. In LabVIEW versions 6i and above, all controls have added a special property called DataSocket Connection. This property allows existing LabVIEW DAQ applications to be transformed into DAQ applications with remote data acquisition capabilities. Client and server software are installed on the client machine and DAQ server respectively, and DataSocket Server is run on both. Then, the server software runs on the DAQ server, and the client software runs on the client machine. This allows remote data acquisition by controlling the server software from the client machine, realizing the networking of virtual instruments. 4. Conclusion With the continuous improvement of Ethernet performance, its determinism is better and its price is lower. At the same time, virtual instruments have strong vitality, which is unmatched by traditional test instruments. The design concept of virtual instrument technology was used to construct and develop an automated test system and network it, realizing remote testing of large, complex, and dangerous systems. With the development of network technology and its widespread application in the testing and instrumentation fields, Ethernet-based virtual instrument network testing technology will inevitably be widely used, bringing a new stage to the development of test systems. References [1] G. Bucci, E. Fiorucci, and C. 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