Embedded network is a network system used to connect various embedded systems so that they can transfer information and share resources with each other. Embedded system uses different connection technology in different occasions, such as home information network in the home room, fieldbus in the field of industrial automation, mobile communication network in the mobile information equipment and other embedded systems, in addition, there are some special connection technology used to connect embedded system.
1 Fieldbus network
Field Bus (Field Bus) is in the mid – 1980 – s following the analog instrument control system, digital control system and centralized distribution control system, developed a computer control technology, it is one of the hot spot of today’s automation control technology development, often also referred to as computer local area network (LAN) in the Field of industrial automation.
Fieldbus is a network that connects digital sensors, converters, industrial instruments and control actuators with industrial process control units and field operation stations. It has the characteristics of full digital, decentralized, bi-directional transmission and multi-branch, and is the product of the development of industrial control network to the field level.
Fieldbus is a low bandwidth low-level control network located at the bottom of production control and network structure, so it is also called Infranet. It is mainly used in production site to realize bidirectional, serial and multi-node digital communication between measurement and control devices. Fieldbus control System (FCS) is a control system that uses fieldbus to connect each controller and instrument equipment. The control system will completely lower the control function to the site and reduce the installation cost and maintenance cost. In fact, FCS is an open, interoperable and thoroughly decentralized distributed control system.
The embedded field control system puts the special microprocessor into the traditional measurement and control instrument and makes it have the digital calculation and communication ability. It USES twisted-pair cable, power line or optical fiber as the bus, such as multiple measuring control instrument connected into a network, and according to the standard communication protocol, in the field of microcomputer-based measuring control between equipment and field instruments and remote monitor computer, realizes the data transmission and information exchange, has formed a variety of automatic control system applicable to actual need.
In short, the fieldbus control system turns the single scattered measurement and control equipment into network nodes, and takes the fieldbus as the link, so that these scattered equipment can communicate with each other to complete the automatic control task of the network system. With the help of fieldbus technology, the traditional single decentralized control equipment has become a whole which communicates with each other and works cooperatively.
Family information network
Home information network is a local area network that connects personal computers, household appliances, water, electricity, gas meters, lighting equipment, network equipment, and security equipment together. Its main function is to centrally control the above-mentioned devices and connect them to the Internet to share network resources and services.
In addition, the family information network can also be extended to the whole house or even the whole community, become the basis of intelligent residential community and intelligent society. In the home information network system, all household equipment is intelligent, including household appliances, water, electricity, gas meters, and lighting equipment. They can communicate with each other and access the Internet through a home gateway. The realization of family information network provides people with a more safe, convenient and comfortable family environment. For example, when the owner goes out, the door is automatically closed and locked, and the monitoring system is automatically opened. In the home, abnormal situations can be automatically notified to the owner. All kinds of equipment in the home can be controlled anytime and anywhere, and the instrument data can be automatically uploaded.
Home information network needs to solve two basic problems: (1) how to connect household appliances, water, electricity, gas meters, lighting equipment and so on. (2) how to realize the interoperability between these connected devices, that is, devices on the home information network can automatically request services when needed, and related devices can provide services or accept requests and process them.
Home information network can adopt different topologies, such as bus, star structure, etc. The home information network can be further divided into a number of control subnets and data subnets, which is similar to the field bus, is a low bandwidth, mainly used for sending and receiving control information network. However, data subnets have high requirements on bandwidth, and the devices connected to them need to transmit a large amount of data information.
Wireless data communication network
In recent years, with the rapid development of mobile phone communication, the rapid popularity of personal computers, a variety of portable computers, such as laptop computer, notebook computer, handheld computer and other rapid increase, data communication between fixed computers can not meet the needs.
People hope that data information can be transmitted and exchanged anytime and anywhere, so data communication transmission media began to expand from wired to wireless, wireless mobile data communication appeared. Wireless data communication network is a network system that transmits data through radio waves. It is developed on the basis of wired data communication and can realize data communication in mobile state. Through wireless data communication networks, smartphones, PDAs and laptops can exchange data and access the Internet.
Wireless data communication networks are divided into short-range wireless networks and wireless Internet. Short-range wireless networks mainly include 802.11, Bluetooth, IrDA and HomeRF.
Wireless Internet or mobile Internet mainly uses two kinds of wireless connection technology: one is mobile wireless access technology, such as GSM, GPRS, CDPD (Cellular Digital Packet Data), etc. The other is fixed wireless access technology, including microwave, spread spectrum communication, satellite and wireless optical transmission.
4 Embedded Internet
With the rapid development of Internet and embedded technology, more and more information appliances, such as Web video phone, set-top box and information appliances and other embedded system products are required to connect with the Internet. To share the convenient, fast, ubiquitous information resources and services provided by the Internet, that is, embedded Internet technology. Embedded Internet technology has a broad application prospect in intelligent transportation, household management system, home automation, industrial automation, POS and e-commerce.
4.1 Access mode of embedded Internet
The embedded device integrates the TCP/ IP protocol stack and related software. Such device can be used as a node of the Internet, assigned with IP address, and directly connected to the Internet.
The characteristics of this access mode are:
- The device can connect to the Internet and access the Internet transparently. No special access equipment is required;
- Protocol standardization of equipment;
- Relatively high processor performance and resources are required;
- It needs to occupy IP resources. Due to the current shortage of IPv4 resources, this scheme may be more realistic in IPv6 networks.
Access the Internet through the gateway in the thin device solution, the device accesses the Internet through the access device instead of directly accessing the Internet and does not need the complete set of complex TCP/ IP protocols. For example, Embedded Micro Internet -workingTechnology (EMIT) is a technology that connects Embedded devices to Internet. The characteristics of this access mode are:
- Low requirements on the performance and resources of access devices;
- The protocol stack cost of access device is low.
- There is no need to assign a valid IP address.
- Can reduce the overall cost of the system;
- The equipment can realize diversification and miniaturization.
4.2 Embedded TCP/IP protocol stack
The embedded TCP/IP protocol stack performs the same functions as the complete TCP/IP protocol stack, but some indicators and interfaces of the embedded protocol stack may be different from those of the common protocol stack due to the resource limitation of the embedded system.
(1) The call interface of embedded protocol stack is different from that of ordinary protocol stack
The socket interface of the common protocol stack is standard and the application software is compatible. However, the code overhead, processing and storage overhead of implementing the standardized interface are huge. Therefore, when the standard protocol stack interface is transplanted to the embedded system, most manufacturers have made varying degrees of modification and simplification, and established efficient special protocol stack, the API provided by them may not be completely consistent with the API of the general protocol stack.
(2) Clipping of embedded protocol stack
The embedded protocol stack is mostly modularized. If the memory space is limited, it can be installed dynamically when it is needed. Moreover, interface forwarding, a full set of Internet service tools and other non-essential parts for embedded systems are omitted.
(3) Platform compatibility of embedded protocol stack
The common protocol stack is closely combined with the operating system, and most of the protocol stack is implemented in the operating system kernel. The implementation of the protocol stack depends on the services provided by the operating system, so the portability is poor. The implementation of embedded protocol stack is generally not dependent on the operating system, so it is easy to transplant. Many commercial embedded protocol stacks support multiple operating system platforms.
(4) High efficiency of embedded protocol stack
The implementation of embedded protocol stack usually takes up less space, requires less data storage, and high code efficiency, thus reducing the requirements on processor performance.
