Combining a modem with a router is called a cellular modem router. A modem is not a router, a modem is also called a cat. A router is a computer networking device that transmits packets of data to a destination (chooses the data transmission path) through a network, a process called routing. A router is a device that connects two or more separate networks. Routing works at the third layer of the OSI model - the network layer, such as the Internet Protocol layer.
1. Is the modem a router?
A modem is a communication device developed to solve the problem of using analog channels to transmit digital signals. Computers can only process digital signals, and some existing channels can only transmit analog signals. In order to use analog channels to transmit signals, the transmitter must convert the digital signals into analog signals, and modulate the digital signals to be sent onto the carrier. , the wave signal is an analog signal and can be transmitted on an analog channel. Then, the receiving end performs corresponding processing to restore the transmission word signal, and this process is demodulation. In this way, the purpose of transmitting digital signals on an analog channel is achieved.
The cat is a modem , which is used to access the Internet through telephone lines ( including ADSL broadband and ordinary telephone lines ) , and the modem is used to form a local area network ( including wireless and wired ) computer online. Directly to the cat is faster. Most of the wired connections after connecting to the cellular modem router have negligible speed degradation, and wireless speeds are not as fast as wired ones.
The cat is used for network signal transfer of different media between networks, such as converting ADSL, optical fiber, cable communication, etc. network signals into standard computer network signals. A cellular modem router is used to redistribute network signals, simply to allow one network cable to connect more computers. If you have broadband at home, you must have a cat. If you have multiple computers to access the Internet, you must have a router. If there are many computers, you need to expand the interface of the switch if the number of interfaces exceeds the router.
To put it simply: a modem converts the pulse signal sent by the telephone line into a digital signal that the computer can accept, and then converts the digital signal from the computer into a pulse signal. As for the cellular modem router, because there is only one network cable for the cat to connect to the computer, and if you want to connect multiple computers, the router plays this role. Plug the network cable from the cat that connects to the computer to the router. There are multiple ports on the router, and then separate them. Connect to different computers. Several computers connected by a cellular modem router form a small "local area network".
2. What does modem mean?
A modem is a piece of computer hardware that translates a computer's digital signals into pulsed signals that can be sent along an ordinary telephone line, which in turn can be received by another modem on the other end of the line and translated into a computer-understandable language. This simple process completes the communication between the two computers.
In fact, it is the abbreviation of Modulator and Demodulator, which is called modem in Chinese. According to the homonym of Modem, it is affectionately called "cat".
The so-called modulation is to convert the digital signal into an analog signal transmitted on the telephone line; demodulation is to convert the analog signal into a digital signal. Collectively called modems.
The English of the modem is MODEM, its function is the "translator" of the analog signal and the digital signal. There are two kinds of electronic signals, one is "analog signal" and the other is "digital signal". The telephone line we use transmits analog signals, and the transmission between PCs is digital. So when you want to connect your computer to the Internet over a phone line, you have to use a modem to "translate" the two different signals. After connecting to the Internet, when the PC sends information to the Internet, since the telephone line transmits an analog signal, a modem must be used to "translate" the digital signal into an analog signal before it can be sent 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 is an analog signal, if the PC wants to understand them, it must use the "translation" of the modem. This process is called "demodulation".
Modems are called "cats", short for MODULATER and DEMODULATER. We know that the language between computers is a digital signal composed of 0s and 1s, while the signal transmitted by the telephone line is an analog signal. Each group of transmissions requires a pair of MODEMs to complete. The A-Modem on the A-machine converts the digital signal of the A-machine into an analog signal that can be used for telephone line transmission, and transmits it to the B-Modem through the telephone line. The B-Modem then converts the received analog signal into a computer that can recognize. The digital signal is transmitted to the second computer, so that the communication between the two computers is realized.
A-Machine and A-Modem are your computer and demodulator, B-Machine and B-Modem are dial-up servers at one end of the telecommunications bureau. After the connection is made, the computer establishes a physical connection with the dial-up server at one end of the telecommunication bureau. On the basis of the physical connection, Internet services can be enjoyed.
Modems used on ordinary telephone lines are called analog modems. The 56K analog modem has a theoretical maximum download rate of 53,333Bps on normal lines, and a maximum upload rate of 33.6KBps.
On an ordinary telephone line, two 56K modems are used for connection, and the maximum connection rate is 33.6K. This is because the download of A-Modem is an upload for B-Modem, while the download of B-Modem is an upload for A-Modem. Limited by the modem upload rate of up to 33.6KBps on ordinary lines, and the maximum connection rate of 33.6K. The vast majority of 33.6K Modem have been discontinued.
On ordinary telephone lines, connecting with ISPs that provide 56K access such as 163, 167, etc., can usually reach a connection speed of about 50K. This is because the modems at the central office such as 163 and 167 are digital Modems. If they are matched with a suitable Modem, they can reach or exceed the theoretical value on ordinary lines with better quality.
3. Types of Modem
Generally speaking, according to the shape and installation method of Modem, it can be roughly divided into the following four categories:
3.1 External Modem
The external Modem is placed outside the chassis and is connected to the host through the serial communication port. This Modem is convenient and dexterous, easy to install, and the flashing indicator light is convenient to monitor the working status of the Modem. But the external Modem needs to use extra power supply and cable.
3.2 Built-in Modem
The built-in Modem needs to disassemble the case during installation, and needs to set the interrupt and COM port, and the installation is complicated. This Modem needs to occupy the expansion slot on the motherboard, but does not require additional power and cables, and the price is cheaper than the external Modem.
3.3PCMCIA plug-in Modem
Plug-in Modem is mainly used in notebook computers, and the volume is slim. With the mobile phone, mobile office can be easily realized.
3.4 Rack Modem
The rack-mounted Modem is equivalent to concentrating a group of Modem in a box or shell, and is powered by a unified power supply. Rack Modem is mainly used in the central computer room of Internet/Intranet, telecommunication bureau, campus network, financial institution and other networks.
In addition to the above four common Modems, there are now ISDN modems and a modem called Cable Modem, and there is also an ADSL modem. Cable Modem uses the cable of cable TV for signal transmission. It not only has the function of modulation and demodulation, but also integrates cellular modem routers, hubs and bridges. The theoretical transmission speed can reach more than 10Mbps. Internet access through Cable Modem, each user has an independent IP address, which is equivalent to having a personal dedicated line. At present, Shenzhen Cable TV Station Tianwei Network Company has launched this kind of Internet access service based on the cable TV network, and the access rate is 2Mbps-10Mbps!
