NCERT Solutions for Computer Science Class 12 Chapter 10: Computer Networks

The arrangement of computers and other peripherals in a network is called topology. The popular network topologies are Mesh, Ring, Bus, Star and Tree.

A network is an interconnected collection of autonomous computing devices that can share and exchange information and resources.

A few commonly used networking devices are modem, hub, switch, router etc.

(a) ARPANET — Advanced Research Project Agency Network

(b) MAC — Media Access Control

(c) ISP — Internet Service Provider

(d) URI — Uniform Resource Indicator

When two universities located in different states want to transfer information between them, they would use a Wide Area Network (WAN). WANs are designed to connect devices over long distances, such as between different cities, states, or countries.

The two main advantages of using a network of computing devices are as follows:

1. Resource Sharing — Through a network, data, software and hardware resources can be shared irrespective of the physical location of the resources and the user.

2. Reliability — A file can have its copies on two or more computers of the network, so if one of them is unavailable, the other copies could be used. That makes a network more reliable.

Tree topology is a hierarchical structure where multiple branches can each have one or more basic topologies, such as ring, bus, or star. In this type of network, data transmitted from the source first reaches the centralized device, and from there, the data passes through every branch where each branch can have links for more nodes.

In bus topology, each communicating device connects to a transmission medium known as a bus. Data sent from a node are transmitted along the length of the bus in both directions. As a result, data can be received by any of the nodes connected to the bus.

(a) Bus Topology

(b) Star Topology

A modem is a computer peripheral that allows us to connect and communicate with other computers via telephone lines. Modem stands for 'Modulator Demodulator'. The modem at the sender’s end acts as a modulator that converts the digital data into analog signals. The modem at the receiver’s end acts as a demodulator that converts the analog signals into digital data that the destination node can understand.

(a) Switch — A switch is a networking device that connects various computing/network devices on a computer network using packet switching to receive and forward data to the destination. When data arrives, the switch extracts the destination address from the data packet and stores it in a table to determine where to send the packet. This allows the switch to send signals to only selected devices instead of broadcasting to all devices. Additionally, a switch can forward multiple packets simultaneously. One of the key features of a switch is that it does not forward noisy or corrupted signals. Instead, it drops such signals and requests the sender to resend them.

(b) Repeater — A repeater is a device that amplifies a signal being transmitted on the network. It is used in long network lines, which exceed the maximum rated distance for a single run. Over distance, the cables connecting a network lose the signal transmitted. If the signal degrades too much, it fails to reach the destination. Or if it does arrive, the degradation of the message makes it useless. Repeaters can be installed along the way to ensure that data packets reach their destination.

(c) Router — A router is a network device that forwards data from one network to another. A router works like a bridge but can handle different protocols. Based on a network road map called a routing table, routers can help ensure that packets are travelling the most efficient paths to their destinations. If a link between two routers fails, the sending router can determine an alternate route to keep traffic moving.

(d) Gateway — A gateway is a network device that connects dissimilar computer networks following different protocols. The gateways act as entry and exit point for a network as they translate communications from one network protocol to the other.

(e) NIC — The network interface card (NIC) is a device that is attached to each of the workstations and the server. It helps the workstation establish the all-important connection with the network and has a unique number identifying it, known as the node address.

Star Topology

Bus Topology

The MAC (Media Access Control) address is the physical address, which is assigned to the hardware network card (Network Interface Card), of the host computer and remains fixed. The machine on which the NIC is attached, can be physically identified on the network using its MAC address. The NIC manufacturer assigns a MAC address which is a 6 byte address (48 bits) with each byte separated by a colon. The first three bytes (24 bits) of MAC address are the manufacturer-id or the organizational unique identifier (OUI) and the last three bytes (24 bits) are the card-number.

IP address, also known as Internet Protocol address, is a unique address that can be used to uniquely identify each node in a network. However, unlike MAC address, IP address can change if a node is removed from one network and connected to another network. A sample IP address looks like: 192.168.0.178.

The MAC (Media Access Control) address is the physical address, which is assigned to the hardware network card (Network Interface Card), of the host computer and remains fixed. The machine on which the NIC is attached, can be physically identified on the network using its MAC address. A sample MAC address looks like: FC:F8:AE:CE:7B:16.

The character based naming system by which servers are identified is known as domain name system (DNS). DNS helps to translate domain names into IP addresses that computers can understand. It acts as a directory that matches human-readable domain names to their corresponding numerical IP addresses, allowing users to access websites without needing to remember or type in the IP addresses directly.
A DNS server is a specialised server responsible for finding the correct IP address for a given domain name. Domain Name Servers are the phone book of the Internet.

The World Wide Web (WWW) is a set of protocols that allows us to access any document on the Net through a naming system based on URLs. The WWW also specifies a way, known as the Hypertext Transfer Protocol (HTTP), to request and send hypermedia documents over the Internet.

The Internet is a worldwide network of computer networks that allows all computers to exchange information with each other. They follow protocols like TCP/IP (Transmission Control Protocol/Internet Protocol) for communication.

The WWW is a small part of the Internet. We can say that the Internet is a highway that offers many services and features, and the WWW is a vehicle (like a truck) that uses this highway to transport information.