Cats, routers, and switches belong to the network layer of the computer network system and are the connected devices used to connect the PC to the Internet. Let's take a look at their role.
Cat
Modem, also known as modem, is the abbreviation of Modulator and Demodulator. It is a device that converts a digital signal into an analog signal by modulation at the transmitting end and converts the analog signal into a digital signal by demodulating at the receiving end. Its role is to "translators" of analog and digital signals.
There are two types of electronic signals, one is "analog signal" and the other is "digital signal". The telephone line we use transmits analog signals, and the digital signals are transmitted between PCs. So when you want to connect your computer to the Internet via a telephone line, you must use a modem to "translate" two different signals. After connecting to the Internet, when the PC sends information to the Internet, because the telephone line transmits an analog signal, it is necessary to use a modem to "translate" the digital signal into an analog signal before it can be transmitted to the Internet. This process is called "modulation." ". When a PC obtains information from the Internet, since the information transmitted from the Internet through the telephone line is an analog signal, the PC wants to understand them, and must also use the modem to "translate". This process is called "demodulation." . In general, it is called "modulation and demodulation."
router
A router (Gateway) is a device that connects to various local area networks and wide area networks in the Internet. It automatically selects and sets routes according to the channel conditions, and sends signals in the optimal path in the order of the front and back. The router is the hub of the Internet, "traffic police." Its role is to connect multiple logically separate networks.
The so-called logical network represents a single network or a subnet. When data is transferred from one subnet to another, it can be done through the routing function of the router. Therefore, the router has the function of judging the network address and selecting the IP path. It can establish a flexible connection in a multi-network interconnection environment, and can connect various subnets by completely different data packets and media access methods, and the router only accepts the source station or The information of other routers is an interconnected device at the network layer.
switch
A switch means that a switch is a network device used for electrical (optical) signal forwarding. It provides an exclusive electrical signal path for any two network nodes that access the switch.
Switching is a general term for the technology of sending information to be transmitted to the corresponding route that meets the requirements by means of manual or automatic completion of the information in accordance with the need to transmit information at both ends of the communication. Switches can be classified into WAN switches and LAN switches depending on the working location. A wide-area switch is a device that performs information exchange functions in a communication system and is applied to the data link layer. The switch has multiple ports, each with a bridge function that can be connected to a LAN or a high-performance server or workstation. In fact, switches are sometimes referred to as multiport bridges.
to sum up
Simply speaking, a cat is equivalent to a repacking factory. A router is equivalent to a wholesale retailer, and a switch is equivalent to a logistics distribution. The analog signal transmitted by the general network cable needs to be converted into a digital signal by the cat, and then sent to the PC through the router. If the number of the PC end exceeds the connection limit of the router, the switch needs to be installed. Therefore, if you have broadband at home, you must have a cat. If you have multiple computers, you must have a router. If there are many computers, you need a switch expansion interface that exceeds the number of interfaces on the router.
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