Introduction to Networking

Communication Devices

Communication devices are hardware that are used on both ends (sender and receiver) to transmit data.

  • The Communication device at the sending end sends the data through a communication medium.
  •  The Communication device at the receiving end receives the data through a communication medium.

Communication devices may convert analog data to digital data or digital data to analog data according to requirements.

Types of Communication devices are explained below

1. Dial up modem

  • The modem is a communication device that sends and receives data from one computer to another on the internet through telephone lines.
  • Connection is established by dialing a number from the phone.
  • Sending and receiving computers both must have dial-up modes.
  • The computer sends the digital data, and the Modem converts it into analog signals to transmit it over the telephone lines; it’s called modulation.
  • The modem at the receiving end converts the analog signals back into digital signals to transmit them to the receiving computer, which is known as demodulation.
  • The dial-up connection must be re-established each time the modem is used.
  • Data transfer speed is much slower, up to 56 Kbps. The dial-up modem is not used nowadays.
  • It is replaced with Digital modems.

Computer 1 -> modem-> antenna -> antenna -> To ISP provider -> internet -> from ISP -> antenna -> antenna -> modem -> Computer 2

2. Digital modem

The digital modem is also called a broadband modem. Types of digital modems are

  • ISDN modem
  • DSL modem
  • Cable modem

3. Wireless Modem

  • Wireless modem transfers data through the air instead of cables.
  • Wireless modem, also known as radio frequency modem.
  • It is used in notebooks, desktop computers, smartphones, handled computers, and other devices to connect to the internet.

4. Network interface card (NIC)

  • NIC is used to connect a computer to the internet.
  • It is a circuit board installed on the motherboard.
  • Nowadays, most computer systems have built-in NIC on the motherboard.
  • Each computer in the network must have at least one NIC.
  • NIC supports wired and wireless networks

Note: TP-link is an alternative to NIC.

5. Wireless Access Point

6. Repeaters and Amplifiers

  • The repeater is a device that is used to regenerate the original signals to transmit them over a large distance.
  • Repeaters are available both for wired and wireless networks.
  • Digital and analog repeaters are available.
  • Antenna can also be used to increase the range of Wi-Fi networks. The strength of the antenna is measured in decibels (dB)
  • Repeaters work on physical layers, which is why they cannot recognize MAC and IP addresses.
  • Note: if any device is used in the data link layer, then it will use the MAC address, and those devices that are used in the network layer will use the IP address.


  • Repeaters have two ports.
  • It forwards data and can’t send it back.
  • The repeater cannot filter the data. It means it sends data as received.
  • Collision is maximum. It is up to a number of devices.

Repeater vs. Amplifier

The repeater regenerates the signal so that the noise can be reduced or eliminated. The amplifier increases both the amplitude and the noise of the signal.

Let’s explain with an example,

If there is signal X, which is down to half (X/2) after some distance, then the amplifier may increase it up to 2X, 3X.. up to NX. But the repeater is used to regenerate the original signal as X.

7. HUB

  • A hub is a central device that contains multiple ports to connect multiple computers to a network.
  • HUBs are non-intelligent because when the sender sends data to the hub, the hub automatically passes it onto every device/computer on the network through ports.
  • It is used in physical layers like repeaters.
  • One end of the cable is connected to HUB, and the other is connected to the computer.
  • HUB can handle only one-way information traffic at a time.


  • Hub has many ports to connect different devices. That’s why it is called a multiport repeater.
  • It forwards data and can’t send it back.
  • The repeater cannot filter the data. It means it sends data as received.
  • Collision is maximum. It contains up to a number of devices.

8. Switch

  • Switch is a more intelligent device than HUB.
  • It receives the message from any device connected to the network and transmits this message to only the device for which the message was sent by the sender.
  • The switch works at the data link layer and uses the mac address (physical address) of each device connected to the port of the switch.
  • It can also handle multiple connection channels at the same time
  • “We cannot access the internet by using only a hub or switch.”

 9. Router

A router is a communication device that connects multiple networks using similar or different protocols. It works on the network layer.

  • Hub and switch are used to share the data within the network. Both are not able to access the data outside the network.
  • To access outside the network, a device needs to be able to read IP addresses.
  • Every network has an IP address, and Routers read the IP address of the destination device and send data to that device.
  • It works at three layers: physical, data link layer, and network layer.
  • It checks the MAC address at the data link layer and the IP address at the network layer.
  • An IP address is used to access the internet.


  • If the Router can’t understand where the message is to transfer, then it broadcasts this message to every device connected to the network.
  • It can filter the message.

It uses the routing table and some protocols (RIP protocol, distance vector routing protocol) to transmit the message.

The router uses its own buffer, so collision is a minimum

For example there are three networks A, B and C. when a sends data to C then Router reads the message-data along with destination IP-address and then transmit data to C network.

 10. Gateway

  • A gateway is a device that connects two or more networks with their different types of protocols. . i.e., one network uses the Token Ring protocol, and the other network uses the Ethernet protocol.
  • It is an intelligent device.
  • It converts data according to protocols.
  • The connection of the personal computer to a mainframe computer is an example of a gateway

11. Bridge

Bridges are used in the data link layer but cannot used in the network layer.

A network bridge can be used in computer networks to interconnect two LANS and interconnect separated network segments.

Bridge cannot send the message if the sender and receiver both are present in the same segment. 

12. Multiplexers and concentrators


Multiplexing is a technique that is used to combine different inputs and send multiple data streams over a single medium. It is done by hardware called MUX.

DEMUX is a device at receiving ends that separates a signal into its component signals (one input and n outputs)


The concentrator combines the multiple messages and then sends them through a single transmission medium. It is sent in such a way that all the individual messages are active simultaneously instead of sending as a single combined message.