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An electronic device that can send and receive data on the network is called the communication device. The communication devices are used on both ends of the connections. Most of the communication devices have the ability to convert the digital signal of computer into analog signal so that the signals can be transmitted on the communication line to another end. The reverse is also true. The most important communication devices are described below.
Modem
Modem stands for Modulator and Demodulator. The modem (dialup modem) is an electronic device that can convert the digital signals into analog signals and analog signals into digital signals. It is used on both ends of the computers for data communication between, computers through telephone line. We knew that data is communicated through telephone line in the form of analog signals. So data in the form of digital signal from one computer must be converted into analog signals before to transmit it to another computer through telephone line. Similarly, to receive the data from another computer through telephone line in the form of analog signals must be converted to digital before to store into the computer. The modem can be external or internal.
The external modem is a separate device that is attached to the computer through RS-232 serial port. It can be easily moved from, one computer to another. It has also many functions but it is very costly.
An internal modem is an expansion card that is installed into the expansion slot on the computer’s motherboard. Most of the computers at home and offices use the internal modem because it is less expensive than external modem. The Fax machine also uses the internal card; it is because internal modem is also known as Fax Card.
Digital Modem
The modem that is used to send and to receive data to and from a digital telephone line is called digital modem. The examples of digital modems are ISDN and DSL. These modems send and receive the digital signals to and from the digital line. This modem does not convert the digital signals into analog because digital lines already use the digital signals. Therefore, in this case he definition of modem confuses the users, however manufacturers still use the term modem for devices used in digital line for data communication.
Network Interface Card
It is also referred to as LAN adapter or simply LAN card. It is used in Local Area Network to establish the communication between the devices (computers, printers and other devices) attached on the network. Usually, the personal computers use the network interface card (NIC) in Local Area Network (LAN). The Ethernet card is the most common type of network interface card. The data transmission speed of Ethernet card is from 10 Mbps to 1,000 Mbps. Some of the network interface cards also, have the combined features of Ethernet card and dialup modem card.
Bridge
It is an electronic device that connects two similar networks and controls the data flow between them. A bridge looks at the information in each packet header and forwards data (that is traveling) from one LRN to another.
Router
An electronic device that connects multiple computers together and transmits data to its correct destination using the available path on the network is called router. It stores the routing information of each node or computer on the network and to use these information to transfer data between nodes. Like a bridge, a router looks at each packet’s header to determine where the packet should go and then determines a route for, the packet to take and thus reach its destination; some routers also have built-in antivirus protection. Similarly, some routers also support wireless communications.
Gateway
A gate is an electronic device that can perform logical function. A gateway is a device or system (collection of hardware and software resources) that connects two networks and translates information from one to the other so that data can be transmitted between two dissimilar networks.
Packets from different networks have different kinds of information in their headers, and information can be of different formats. The gateway can take a packet from one type. of network, read the header, and then encapsulates the entire packet into a new one, adding a header that is understood by the second network.
Repeater
A device, which is used to join same type of networks to extend the length of the communication medium, is called repeater. It also amplifies the signals received from one network and sends the amplified signals to another network.