"Modem" is a device that converts digital signals and analog signals. Modem is the collective name of modulator and demodulator. Modulation is to convert digital signals into analog signals transmitted on telephone lines; demodulation is to convert analog signals into digital signals. At the sending end, the modem modulates the digital signal generated by the computer's serial port into an analog signal that can be transmitted through the telephone line; at the receiving end, the modem converts the analog signal input into the computer into the corresponding digital signal and sends it to the computer interface.
#The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
"Modem" is a device that converts digital signals into analog signals.
Modem is the abbreviation of modulator and demodulator. It is a kind of computer hardware that can translate the digital signals of the computer into analog signals that can be transmitted along ordinary telephone lines. These The analog signal can be received by another modem at the other end of the line and translated into a language that the computer can understand. This simple process completes communication between two computers.
Modem is the abbreviation of Modulator and Demodulator. It is called modem in Chinese. According to the homophony of Modem, it is affectionately called "cat". It is a kind of device that can achieve communication needs. Electronic equipment with modulation and demodulation functions. Generally consists of modulator and demodulator. At the sending end, the digital signal generated by the computer's serial port is modulated into an analog signal that can be transmitted through the telephone line; at the receiving end, the modem converts the analog signal input into the computer into a corresponding digital signal and sends it to the computer interface. In personal computers, modems are often used to exchange data and programs with other computers, as well as to access online information service programs, etc. [2] .
The so-called modulation is to convert digital signals into analog signals transmitted on telephone lines; demodulation is to convert analog signals into digital signals. Collectively called a modem.
The English name for modem is MODEM, and its function is the "translator" of analog signals and digital signals. There are two types of electronic signals, one is "analog signal" and the other is "digital signal". The telephone lines we use transmit analog signals, while the PCs transmit digital signals. So when you want to connect your computer to the Internet through a phone line, you must use a modem to "translate" two different signals. After connecting to the Internet, when the PC sends information to the Internet, since the telephone line transmits analog signals, a modem must be used to "translate" the digital signals into analog signals before they can be transmitted to the Internet. This process is called "modulation" ". When the PC obtains information from the Internet, since the information transmitted from the Internet through the telephone line are all analog signals, if the PC wants to understand them, it must also use the "translation" of the modem. This process is called "demodulation" . Generally speaking, it is called "modulation and demodulation".
Transmission mode
Modem was originally used for data transmission only. However, with the continuous growth of user demands and fierce competition among manufacturers, more and more "two-in-one" and "three-in-one" modems have appeared on the market. In addition to data transmission, these Modems also have fax and voice transmission functions.
1. Fax Mode (Fax Modem)
In addition to saving the cost of a dedicated fax machine, faxing through Modem also has many benefits: you can directly fax files from your computer to The computer or fax machine of the other party without printing the document first; the received fax can be conveniently saved or edited; the problem of handwriting gradually fading due to the use of thermal paper in ordinary fax machines can be overcome; because Modem uses With error correction technology, the fax quality is better than that of ordinary fax machines, especially for graphic faxes. Most Fax Modems follow the V.29 and V.17 fax protocols. Among them, V.29 supports a fax rate of 9600bps, while V.17 can support a fax rate of 14400bps.
2. Voice Mode (Voice Modem)
Voice mode mainly provides phone recording messages and full-duplex hands-free calling functions, truly integrating the phone and the computer. Here, it is mainly a new voice transmission mode-DSVD (Digital Simultaneous Voice and Data). DSVD is a voice transmission standard proposed by Hayes, Rockwell, U.s. Robotics, Intel and other companies in 1995. It is an expansion of the existing V.42 error correction protocol. DSVD adopts Digi Talk's digital voice and data simultaneous interpretation technology, allowing the Modem to transmit data and make calls at the same time on ordinary telephone lines.
DSVD Modem reserves 8K bandwidth (some Modems also reserve 8.5K bandwidth) for voice transmission, and the remaining bandwidth is used for data transmission. The voice will be compressed before transmission, then integrated with the data that needs to be transmitted, and transmitted to the other user through the telephone carrier. At the receiving end, the Modem first separates voice from data, and then decompresses and digital-to-analog conversion of the voice signal to achieve simultaneous data/voice interpretation. DSVD Modem has broad application prospects in distance teaching, collaborative work, online games, etc. Since DSVD Modem is more expensive than ordinary Voice Modem, and to realize the data/voice simultaneous interpretation function, the other party needs to use DSVD Modem, which hinders the popularity of DSVD Modem to a certain extent.
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