Preface
Hello everyone, I am Mr. Lin. Today we will take a look at the knowledge points and introductions in the data communication terminal!
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Figure Data communication terminal
The fact is that few laws govern private citizens using radio scanners, which means you have some freedom in this regard. However, there are some limitations to using these devices, and they depend to a lot on where you live.
In many areas of the country, it is legal for ordinary citizens to use radio scanners as long as they do not interfere with any official communication channels - but this varies from place to place.
Generally speaking, radio scanning has two main types of laws: laws designed to prevent interference with emergency services and laws designed to prevent interference with law enforcement actions.
In data communication service, the device used to send and receive data is called a data terminal device (hereinafter referred to as DTE). DTE may be a large, medium or small computer, or a printer that only receives data. Therefore, DTE belongs to the user category, with many types and large differences in functions. From the perspective of computer and computer communication systems: terminals are input/output tools; from the perspective of data communication network : both computers and terminals are called network data terminal devices, referred to as terminals for short.
Since data communication is a communication between a computer or a computer and a terminal, in order to communicate effectively and reliably, both parties in the communication must follow certain procedures, such as synchronization between the sender and receive parties, error control, establishment, maintenance and removal of transmission links, and data traffic control , etc. This function is completed by the communication controller in the network. The above functions in the communication controller are generally implemented through the "protocol" software. Different networks may have different protocol software in the communication controller.
In addition, there are many types of data terminals, including simple terminals and smart terminals, synchronous terminals and asynchronous terminals, local terminals and remote terminals, etc. A synchronous terminal is a terminal that works in frame synchronization mode (such as X.25, HDLC, etc.) and character synchronization mode (such as BSC); an asynchronous terminal is a start and end terminal, adding "start" and "stop" bits to the beginning and end of each character to achieve synchronization between the sender and the receiver. The gap time between the characters and characters can be arbitrarily long, so it is called asynchronous.
data terminals can also be divided into two categories: grouped terminals (PT) and non-grouped terminals (NPT). Packet-type terminals include computers, digital fax machines, intelligent user telegram terminals (Teletex), user packet assembly and disassembly equipment (PAD), user packet switch , dedicated telephone switch (PABX), visual text access equipment (VAP) and local area network (LAN). Non-packet-type terminals include various dedicated terminals such as personal computer terminals, visual text terminals and user telegram terminals.
Figure Mobile wireless terminal
