Recently, the trend of the Internet of Things (IoT) has arisen, and a large number of low-cost sensing and control components have emerged, which has led to the rapid development of smart homes. Various home devices have begun to join the networking and intelligent functions. This change has also allowed automation control applications to gradually enter the homes of ordinary people from larger factories, commercial buildings or public places.
Before the rise of the Internet of Things (IoT) concept, AutomaTIon has a long history of development, from factories, office buildings, ancillary facilities to homes, all of which are automatically controlled. In the early stage, the cost of construction and the integration of hardware and software integration were high. Most of the automatic control was only found in factories, large commercial buildings or facilities, and it has not been popularized for home applications.
In recent years, with the emergence of low-cost sensing and control components, the rapid development of network capture technology, and the rapid spread of various smart devices, the concept of IoT has been proposed, not only the popularity of smart homes, but also the entire field of automatic control. There are also new opportunities. However, it should be the same as the automatic control and IoT field. Sometimes there is a kind of “generation gapâ€. Therefore, this paper will discuss the development trend of related technologies and solutions from the application requirements of automatic control and IoT.
Automatic control gradually moves closer to the IP network
It is believed that those who entered the field of building automation early should be familiar with the Modbus protocol. The Modbus protocol proposed by Modicon in 1979 is a common standard for early control networks because the data format is simple and easy to understand.
The early control network including Modbus is deployed in the physical layer using wired serial communication (Serial). The more common ones are RS422 and RS485. There are quite a few issues to be aware of in this type of serial communication, such as the bit rate of the signal itself (Baud-rate), odd/even function check (Parity), stop bit (Stop Bit) and the interval between messages, etc. The material, length, strand size, serial connection, interference isolation and termination resistance of the wire may affect the communication quality. These factors also make the traditional serial communication control network have higher construction, maintenance costs and implementation technology threshold.
With the development of computer networks, TCP/IP has gradually become a common communication protocol architecture on computer networks, and some traditional control networks have gradually evolved into TCP/IP-based architectures. In response to this trend, the Modbus protocol has evolved from Modbus RTU, which used serial communication in the past, to the use of Ethernet with the TCP/IP protocol architecture, using the Transmission Control Protocol (TCP) transport layer protocol to carry Modbus TCP for the original serial communication content.
Thanks to the simplicity of the Ethernet architecture, the low maintenance cost and the large number of applications in the computer network, compared with the old architecture, Modbus TCP does not have to worry about the complex serial communication signal and wire specifications, making the cost of deployment and maintenance. The technical threshold has been reduced a lot.
Also because of the use of the TCP/IP protocol architecture, the network layer IP protocol can be used for addressing and routing (RouTIng), which also enables Modbus TCP to have a larger range of addressing space and the ability to support larger domains. If equipped with a network bridge (Bridge), it can also be transmitted via network types such as wireless, power line, and fiber, making Modbus TCP suitable for more complex network environments (Figure 1).
Figure 1 The traditional automatic control network can be integrated with the computer network and other IoT networks to create more diversified applications.
On the other hand, with the mass production of electronic components and the reduction of costs, various sensors, controllers and related integration architectures that are closer to the computer network and advertised as low-cost and easy to develop have sprung up. For example, various micro-sensors using ZigBee, Bluetooth low-power (BLE), Arduino, Raspberry Pi, etc., there are also many large-scale investment. These solutions are widely used wirelessly, are easily compatible with computer networks, and under the banner of IoT, have become a new battleground for new military strategists.
Internet of Things facilitates automatic control of software/hardware modernization
It is necessary to construct a network that can be used in various environments and connected devices. Because it is necessary to provide services for a long time, it is impossible to avoid the need to consider reliability and energy efficiency. Various industrial specifications controllers and sensors, which have been widely used in the field of automatic control, have a good performance in terms of reliability and energy efficiency due to their simple structure and long-term product development.
After entering the IoT era, reliability and energy efficiency are facing new challenges due to a greater number of communication needs, more diverse communication content, modes and functional applications.
It may be a good idea to establish a standardized and support-rich architecture. It is now observed that some hardware/software vendors are actively deploying in this direction, such as Apple's HomeKit, Google-led Thread Group, and Intel. OCF IoTIvity and AllSeen AllJoyn headed by Qualcomm, etc. These are integrated service framework solutions for the IoT Protocol Stack and ApplicaTIon Runtime, and even have Part of the commoditization began.
With integrated service architecture solutions, the most convenient is software development and product integration. Software developers can develop applications based on the provided application interface (API). In addition to the lesser integration issues, reliability and information security are also ensured.
Equipment manufacturers only need to have the appropriate service architecture in the upper part of the sensor and controller and meet the relevant specifications, so that the product has good compatibility. In the part of commodity integration, there is a mark that is compatible with a certain service structure, and it is more convenient for the relevant personnel to select products for deployment and even for consumers to purchase.
In addition to the integrated service architecture, the hardware level is the micro operating system used by the controller and sensor. Most of the early products were developed by the manufacturer itself or by a closed micro operating system developed by the software vendor. In recent years, some open source micro-operating systems based on UNIX-like and POSIX operating system architectures have emerged, such as Mbed, Contiki, and FreeRTOS.
This type of operating system is relatively simple, and the processing procedures that must be executed at the same time are much less than the average computer, but the immediacy of data processing must be considered, and there should not be too much delay. Therefore, in addition to the core and software module file size is small, the architecture is also designed and optimized for the controller chip which is more streamlined, and the event-driven, real-time operating system (Real) -time OS) and other conceptual designs to meet the needs.
As far as the design level of the control chip is concerned, there are also many more power-saving and powerful computing chips, with appropriate operating systems, service architectures and applications, which are all important elements for the future IoT popularity. At present, software and hardware manufacturers, and even the open source community, have invested a lot of effort in integrating solutions. Cooperation is more powerful than single-handedness. Through software/hardware integration and optimization, it will let the new state IoT sensing and control components are more likely to meet practical needs in terms of reliability and energy efficiency.
Whether it is IoT or automatic control, the most basic actions when communicating with the device are reading, writing, reading the value captured by the sensor, the switch state of the controller or the set value of the device, etc. Write the switch status, set value, etc. when required. Each device can be thought of as an entity with multiple attribute values.
The early popular Modbus was managed using the concept of a register. Each device has several registers, each of which represents a different switch state, sensed value, set value, and so on. Reading/writing the value on the scratchpad means reading the sensed value or status, or controlling the state of the switch, writing a new setpoint, and so on. The device implementation level only needs to correspond to the state of the sensor, switch, etc. and the scratchpad.
The same concept is also applied to BLE. BLE provides ATT protocol and Generic Attribute Profile. Each device can define several attributes and use the quality of reading and writing attributes to achieve access and control. .
The ER model (Entity-Relation Model) is often used in the field of database and software engineering. Such a concept can also be applied to IoT. Each device can be regarded as an entity (Entity), and each entity has several attributes. The interaction between these entities and attributes is what IoT does.
In the concept of IoT, there will be a larger number and more types of devices on the network, which means that IoT networks require more addressing space and stronger addressing or even routing capabilities than traditional control networks. At the same time, we need to support more diverse data types (Figure 2).
Figure 2 Some common IoT applications and their property examples in life
Network convergence and resource management
In an IoT network with many devices, there may be many different physical network interfaces, such as IEEE 802.11, IEEE 802.15, power line networks, etc. How to aggregate these networks will become an important issue.
In existing Link Layer solutions, a common solution is to bridge different networks so that different types of networks can form connected domains. However, for a network environment where the device has multiple network interfaces and a complex network topology, some heterogeneous network integration solutions are needed.
For example, IEEE 1905.1, implemented by Qualcomm's Hy-Fi solution, is a heterogeneous network aggregation protocol that makes the upper architecture easier to implement and achieves even more with the help of the Abstract Layer. High network efficiency.
In the network layer (Network Layer), the benefits of using an IP network can be used in addition to the above-mentioned network having a larger address space, good routing capability, and easy integration. Network layers and transport layers such as IPSec and TLS can also be used. (Transport Layer) security mechanism. This is one of the reasons why 6LoWPAN will rise. 6LoWPAN is a lightweight network layer protocol designed for IEEE 802.15 members. The header is short and the flexible header definition is given, so that 6LoWPAN can be used without waste. In the case of wide resources, such as the addressing and routing functions of the IP network, and the 6LoWPAN header has the ability to expand and be compatible with the IP network, making it easy to integrate with the entire regional network.
After the lower layers are integrated into the TCP/IP protocol architecture, the rest is the Application Layer. Based on the IoT architecture, Dominique Guinard et al. proposed the WoT (Web of Things) concept in 2009. Many IoT communications will be conducted under HTTP, JSON and other protocol architectures, with CoAP, MQTT or JSON-RPC as events. Notification message push mechanism.
Currently, some integrated service architectures, such as HomeKit, IoTivity, and AllJoyn, provide similar architectures, and related controller operating systems also provide lightweight HTTP servers and browsers to meet this need. This phenomenon also echoes the concept of using the attribute values ​​mentioned above to treat everything. In the case of using HTTP as an application layer protocol, each attribute on each device can be addressed using a URI (Universal Resource Indicator). And access, and JSON uses a streamlined text to express the concept of multiple data types, which also meets the needs of IoT communication (Figure 3).
Figure 3 Network convergence architecture intention, convergence of different types of network technology, not only can put various devices into the domain, but also make the upper application, management mechanism, etc. easier to develop.
Combine cloud to change graphics control software
Graphical, visual monitoring and control are most intuitive to humans. The traditional automatic control will connect each switch and sensor to the central control panel for centralized monitoring. After the computerized operation arises, such work is replaced by computer graphics control software, and the user is used to visualize the various sensors. , the switch to monitor or set some conditional actions, scheduling, and so on.
However, the traditional graphics control software has higher procurement and development costs, and the flexibility of change is not high. Therefore, the graphics control software has been mastered by a small number of software vendors. In the IoT architecture, it is rare to hear anyone mentioning traditional graphics. Control software.
But the need for a graphical user interface still exists, and the aforementioned WoT concept provides a good entry point. Web pages, dynamic web pages, browser-side web applications, web art and other fields are relatively simple and have a large number of developers. The reference materials, various materials, and application interfaces are also very rich, and the web pages can interact with most people. Presented on the device.
The WoT architecture is equivalent to developing the IoT user interface using the concept of developing a web page. The method of sending a URI can be used to read a switch state or sensor and change the state of the switch. Parsing the JSON data returned by the device side, in addition to being able to obtain a certain attribute value, can also be presented in a cool way through a rich visual suite. These features are enough to make the web interface replace the traditional graphics control software.
Another big advantage is that it can easily integrate the cloud interface (API). At present, many cloud services also use HTTP, JSON and other common mechanisms as transmission protocols and data formats. In combination with the benefits of cloud services, in addition to a variety of devices available, or remote access to devices on the IoT network, IoT can also provide services such as energy management, health care, security monitoring, property management, etc. through the cloud. The application is more extensive (Figure 4).
Figure 4 The IoT device has the same communication protocol architecture as the computer network and is equipped with a gateway with IoT concept, which will help integrate various devices on the regional network and interface with cloud services.
This paper starts from the communication needs, from automatic control to IoT, from independent control network to integrated regional network, to explore the development of IoT. In the foreseeable future, devices with IoT will become more popular, and networking and Internet access will be diversified, and the cloud service market will mature.
Under such an overall architecture, the role of the gateway is more important than before. In the past, the gateway mainly provided computers or devices in the regional network to access the Internet. After IoT, the gateway would play a role in integrating different devices and different types of networks. And provide the role of integrated management, cloud Internet service access and other services.
From the earliest automatic control to the current IoT, there are many similarities in nature. Each device is treated with attribute values, and these devices and attributes are addressed and managed. Therefore, between the early automatic control and the current IoT, the "generation gap" does not exist. To some extent, the IoT is even an automatic control of the old bottle, and of course some new concepts are added.
The starting point for the development of various tools and technologies is that it is more convenient for users to use, and it is convenient for developers and operators to develop and maintain. Existing IoT solutions are roughly packaged at the bottom of the application layer, and developers can easily develop applications based on these solutions, so users can enjoy more convenient features.
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