Usage
information in the computer is "0" and "1" composed of digital signals, transmitted over a telephone line can only be an analog electrical signal. Thus, when the two computers via telephone lines for data transmission, requires a device responsible for converting digital-analog. The DAC is the Modem. When the computer sends data, first Modem converts the digital signal into a corresponding analog signal, a process known as "modulation." Before the modulated signal transmitted to another computer through a telephone carrier via Modem also responsible for the recipient to restore the analog signal to a digital signal of the computer can recognize, this process is called "demodulator." It is through such a "modulator" and "demodulator" digital to analog conversion process, enabling remote communication between two computers.
Model Classification
In general, according to the shape and installation Modem, can be divided into the following five categories:
external
external Modem placed on the outside of the chassis, is connected with the host via the serial communication port. Such smart Modem convenient, easy to install, blinking light to facilitate the work of condition monitoring Modem. External Modem but requires additional power cable.
built-in
Modem built-in installation need to disassemble the chassis, and to interrupt and COM port set, installation is more complicated. This takes up Modem expansion slot on the motherboard, but no additional power cable, and the price is cheaper than some of the External Modem.
plug-in
Modem card type is mainly used in notebook computers, slim volume. With the mobile phone, can easily achieve mobile office.
Rack
is equivalent to a set of rack Modem Modem concentrated in a casing or housing, the power is supplied by the regulated power. Rack Modem is mainly used in the central office network of Internet / Intranet, Telecommunications, campus networks and financial institutions.
Similar items
In addition to the above four common Modem, ISDN modems and also called CableModem modem, there is a further ADSL modem. CableModem using a cable television signal transmission cable, not only has the modem function, also set routers, hubs, bridges in a theoretical transmission speed of up to more than 10Mbps. CableModem through the Internet, each user has a separate IP address, which is equivalent with a personal line. Shenzhen Tianwei cable television network has launched this cable network based Internet access service, the access rate of 2Mbps-10Mbps!
new products
Modem initially used for data transmission. However, with the fierce competition between the growing needs of users and manufacturers, more and more of the market there have been some "Combo", "triple play" of Modem. The Modem except for data transmission, voice transmission and further having a facsimile function.
fax mode (FaxModem)
fax through Modem, in addition to cost save a dedicated fax, there are many benefits: you can directly fax files within a computer or fax machine to the other side of the computer, without having to first print out documents; faxes can be received easily save or edit; ordinary fax machines can be overcome due to the use of thermal paper caused by the writing fades problem; due to use error correction technology Modem, fax quality is better than ordinary fax machines, especially for graphics fax even more so. FaxModem mostly follow V.29 and V.17 fax protocol. Which supports V.29 9600bps fax rate, and can support V.17 fax rate of 14400bps.
Voice mode (VoiceModem)
Voice mode is mainly provided telephone message recording and full-duplex speakerphone, really make phones and computers for the financial one. Here, the main is a new voice transmission mode -DSVD (DigitalSimultaneousVoiceandData). DSVD is a voice transmission standards developed by Hayes, Rockwell, U.s.Robotics, Intel and other companies raised in 1995, it is an extension of the existing V.42 error correction protocol. DSVD Digital voice and data by using the same transmission DigiTalk technology, Modem for data transmission line while being in the ordinary telephone call.
DSVDModem
DSVDModem reserved bandwidth of 8K (Modem and some of the reserved bandwidth 8.5K) for voice transmission, the remaining bandwidth is used for data transmission. Before voice transmission will first be compressed and then integrated with the data to be transferred together, sent to other users via telephone carrier. At the receiving end, Modem first voice and data separated, decompressed digital / analog speech signal and then converted to SI data / voice implemented. DSVDModem in distance learning, collaborative work, online games have a wide range of applications. However, due to DSVDModem prices more expensive than ordinary VoiceModem, but also to achieve data / voice with the transfer function, need each other to be used DSVDModem, thereby hindered the popularity of DSVDModem to some extent.
Data Transfer Mode (DTM)
The smart phone "data link" is selected, the phone will automatically search for wireless cat, find their cat after you can log in by entering the account number, the phone's wireless Internet access achieve a.