Computer Networks

Both A and R are true and R is the correct explanation of A.

Explanation
ARPANET, jointly designed and named by the Advanced Research Projects Agency (ARPA) and the US Department of Defense (DoD), was the first computer network and came into existence in 1969. The objective of creating ARPANET was to develop a reliable communication network for the US military defense services, enabling them to send and receive instant messages and share data.

Both A and R are true and R is the correct explanation of A.

Explanation
A router is considered as a more reliable and intelligent device than a hub or switch because it has advanced capabilities to analyze the data being sent over a network, decide or alter how it is packaged, and send it to different computer networks.

Both A and R are true but R is not the correct explanation of A.

Explanation
PANs (Personal Area Networks) are small networks used to establish communication between a computer and other devices in proximity, typically up to 10 meters (20 to 30 sq.ft.). On the other hand, a WAN (Wide Area Network) spans a large geographical area across countries and continents. A WAN can cover an area with a radius spanning hundreds of kilometers.

Both A and R are true but R is not the correct explanation of A.

Explanation
A repeater is a device that amplifies a signal transmitted across the network so that the signal is received in the same way it is sent. A hub is a hardware device used to connect several computers together using different ports.

Both A and R are true and R is the correct explanation of A.

Explanation
VoIP stands for Voice over Internet Protocol, and it is a technology that allows us to make voice calls using a broadband connection instead of a regular phone line. The voice calls are first digitized, compressed, and then fragmented into small packets, which are then relayed by Internet Protocol (IP) across the network.

A is false but R is true.

Explanation
Bus topology is a multi-point configuration where several devices are connected to a main long cable, usually a coaxial cable, which acts as a backbone. This topology is cost-effective to install compared to other network topologies due to the simplicity of its design. Because there is only one communication line (the bus) and no additional networking hardware like switches or hubs needed, the overall setup cost is lower.

A is true but R is false.

Explanation
Infrared (IR) is a wireless technology used for data communication. Infrared involves the usage of electromagnetic radiation, specifically infrared light, to send data. The data is transmitted through the air and can propagate in open space; however, it cannot penetrate the walls of a room and is affected by distance, noise, and heat. It is an example of a short-range wireless network.

A is true but R is false.

Explanation
A protocol defines the set of rules and regulations applicable for data sharing and communication over a network. It is a formal description of message formats and the rules that devices must follow to exchange those messages. However, Local Area Network (LAN) is not an example of a protocol, rather, it is a type of computer network.

Both A and R are true and R is the correct explanation of A.

Explanation
A Gateway is a network device that connects dissimilar networks. Gateway provides the necessary translation of data received from network into a format or protocol recognized by devices within the internal network establishing an intelligent connection between the two.

All of these

Reason — A computer network is a collection of interconnected computers and other hardware devices using communication channels to share data and various resources, including hardware and software resources.

To connect LANs

Reason — Bridges are devices that connect one LAN to another LAN that uses the same protocol.

Source and Destination address

Reason — Each IP packet in a computer network must contain both the source address (the address of the sender or originator) and the destination address (the address of the intended recipient). This ensures that the packet is routed correctly through the network to reach its destination.

WAN

Reason — A WAN is a type of computer network that spreads over a large geographical area across countries and continents, while satellite, microwave, and radio wave are different communication channels.

Metropolitan Area Network

Reason — MAN stands for Metropolitan Area Network.

Optical Fibre Cable

Reason — An optical fiber cable is an example of guided media, also known as wired networking technology.

Bus

Reason — Bus topology is a multi-point configuration, i.e., several devices are connected to a main long cable (usually co-axial cable) which acts as a backbone.

PAN

Reason — PAN is the smallest network, it covers a very small area, usually within the range of 10 meters.

HTTP

Reason — Hyper Text Transfer Protocol (HTTP) is the set of rules for transferring hypertext content on World Wide Web.

Star topology

Reason — In a star topology, each communicating device is connected to a central controller called a hub or switch. This setup ensures that each device has its own dedicated connection to the central hub.

Test a network device

Reason — The ping command is used to test a network device by sending ICMP (Internet Control Message Protocol) echo request packets and receiving ICMP echo reply packets. This process helps determine the connectivity and responsiveness of the network device, such as a router, server, or another computer on the network.

VoIP

Reason — VoIP (Voice over Internet Protocol) is a communication methodology designed to deliver both voice and multimedia communications over Internet protocol.

The Internet is a world-wide network of computer networks. It connects many smaller networks together and allows all the computers to exchange information with each other.

A network is a collection of interconnected computers and other devices to share data and other resources (hardware and software resources).

The various types of topologies are as follows:

1. Bus or Linear topology
2. Ring or Circular topology
3. Star topology
4. Tree topology
5. Mesh topology

The range of frequency for radio waves is between 3 KHz to 1 GHz.

1 Gbps is equal to 1000000000 bits per second. Therefore, to convert 18 Gbps to bits per second:

18 Gbps = 18 * 1000000000 = 18000000000 bits per second

So, 18 Gbps is equal to 18,000,000,000 bits per second.

(a) Bandwidth — Bandwidth of a channel is the range of frequencies available for the transmission of data through that channel. The higher the bandwidth, the higher the data transfer rate. Bandwidth is calculated as the difference between the maximum and minimum frequencies contained in the composite signals, and it is measured in Hertz (Hz).

(b) Bluetooth — Bluetooth is a short-range wireless technology used to connect devices like mobile phones, mouse, headphones, keyboards, and computers wirelessly over short distances. It enables tasks such as printing documents with Bluetooth-enabled printers without the need for physical connections. These devices utilize a low-cost transceiver chip that operates within the unlicensed frequency band of 2.4 GHz for data transmission and reception. Bluetooth devices can communicate within a range of 10 meters, achieving speeds of 1-2 Mbps. The technology allows up to 255 devices to form a network, with 8 devices capable of simultaneous communication while others remain inactive until prompted by the master device.

(c) DNS — DNS, known as the Domain Name System, serves as the phonebook of the Internet. It provides a character-based naming system for servers, allowing users to access websites using easy-to-remember domain names like google.com instead of numeric IP addresses such as 8.8.8.8. DNS is essential for internet navigation as it translates domain names into IP addresses, enabling seamless communication and resource access across the web.

(d) Data transfer rate — Data transfer rate is the number of bits transmitted between source and destination in one second. It is also known as bit rate. It is measured in terms of bits per second (bps). The higher units for data transfer rates are: 1 Kbps = 210 bps = 1024 bps 1 Mbps = 220 bps = 1024 Kbps 1 Gbps = 230 bps = 1024 Mbps 1 Tbps = 240 bps = 1024 Gbps

(e) HTTP — HTTP stands for HyperText Transfer Protocol, which is the primary protocol used to access the World Wide Web. It is a request-response protocol (also called client-server) that runs over TCP. HTTP facilitates access to hypertext from the World Wide Web by defining how information is formatted and transmitted, and how web servers and browsers should respond to various commands.

For example, whenever we enter the URL http://www.ncert.nic.in in a browser, it sends an HTTP request to the web server where ncert.nic.in is hosted. The HTTP response from the web server fetches and sends the requested web page, which is then displayed on the browser.

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.

Star Topology

Bus Topology

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.

1. Bus topology — Bus topology is a multi-point configuration, i.e., several devices are connected to a main long cable (usually co-axial cable) which acts as a backbone. Nodes are connected by drop lines and taps. A drop line is a connection between long cable and devices and taps are the connectors that are punctured inside the main cable. The data flows from one end of the cable to the other. The cable has terminators at both ends which absorb signals when the signal reaches the end, preventing signal bounce. However, as the signal travels a long distance, it becomes weaker and weaker. It works well for small networks.
2. Star Topology — In star topology, each communicating device is connected to a central controller called a hub or switch. The devices in star topology send and receive data indirectly, the data passes to and from the hub. The central node can be either a broadcasting device (hub) or a unicast device (switch).

(a) Baud — Baud refers to the number of discrete signal elements transmitted per second. It is the measuring unit of the data transfer rate.

(b) Communication channel — Communication channel is also known as transmission media through which data or signal is transferred between two communicating devices, i.e., from one system to another system, through wires or without wires.

(c) Hub — A hub is a networking device having multiple ports that are used for connecting multiple computers or segments of a LAN together.

(d) Repeater — A repeater is a device that amplifies a signal transmitted across the network so that the signal is received in the same way it is sent.

A MODEM (Modulator Demodulator) is an electronic device that enables a computer to transmit data over telephone lines. It is a device used to convert digital signals into analog signals and vice versa.

The functioning of internal modem and external modem is as follows:

1. Internal modem — These are attached to the internal slot of the motherboard. They modulate digital data into analog signals for transmission and demodulate incoming analog signals into digital data.
2. External modem — It is a small box connected to the communication port of the computer. It works similarly to the internal modem. The only difference is that it is placed outside the CPU box.

(a) PPP — Point-to-Point Protocol (PPP) is one of the most commonly used data link protocols. It is utilized to establish a direct connection between two nodes and can provide various functionalities such as connection authentication, transmission, encryption, and compression. Communication occurs through a high-speed modem, and PPP is used to connect telephone dial-up lines to the internet.

(b) POP3 — Post Office Protocol version 3 (POP3) is a simple and standard method for accessing mailboxes and downloading messages to local computers. Users can receive messages using the POP3 protocol. An advantage of POP3 is that once messages are downloaded, an internet connection is no longer necessary to read the mail, as they are saved on the computer's hard disk.

(c) VoIP — Voice over Internet Protocol (VoIP) is utilized for transmitting voice communications. Voice calls undergo digitization, compression, and fragmentation into small packets, which are then transmitted across Internet Protocol (IP) networks. VoIP implementation allows users to carry voice traffic efficiently over an IP network.

(d) IRC — Internet Relay Chat (IRC) is an application layer protocol that enables users to share text messages. The sender sends a request to an IRC server, which then forwards the request to another client, facilitating communication between users.

(a) Routers — A router is a networking device that forwards data packets from the source machine to the destination machine over a network using the shortest path available. It can handle different protocols and operates at the network layer, the third layer of the OSI model. Routers utilize IP addresses to connect local area networks to the Internet. In contrast to a hub or a switch, a router possesses advanced capabilities as it can analyze the data being transmitted over a network, make decisions on how it is packaged, and route it to different computer networks.

(b) Bridges — A bridge is a device that operates at both the physical layer and the data link layer of the OSI model. It connects multiple network segments (LANs) at the data link layer (Layer 2) of the OSI model. It is a smarter hub as it can filter network traffic on the basis of the MAC addresses.

(c) Gateways — A gateway is a network device that connects dissimilar networks. It provides the necessary translation of data received from one network into a format or protocol recognized by devices within another network. A gateway establishes an intelligent connection between a local area network and external networks with completely different structures.

A WiFi card is either an internal or external Local Area Network adapter with a built-in wireless radio and antenna. It is used in a desktop computer to enable a user to establish an Internet connection. WiFi cards are known as wireless fidelity cards because they allow users to set up connections without any wires.

A communication protocol is a formal description of message formats and the rules that two or more machines must follow to exchange those messages.

The reason that the Internet works at all is that every computer connected to it uses the same set of rules for communication. The communication protocol used by Internet is TCP/IP.

1. The TCP or Transmission Control Protocol is responsible for dividing the­ file/message into packets on the source computer. It is also responsible for reassembling the received packets at the destination or recipient computer.

2. The IP or Internet Protocol is responsible for handling the address of destination computer so that each packet is routed (sent) to its proper destination.

HTTPS stands for Hypertext Transfer Protocol Secure. It's a protocol that secures communication between two systems, like a browser and a web server, by encrypting data during transmission. When a user accesses a website using HTTPS, a secure connection is established, verifying the server's identity with digital certificates. This encryption and authentication ensure data privacy and integrity, crucial for protecting sensitive information such as passwords and financial data from interception or tampering by malicious entities on the Internet.

Ethernet is a LAN architecture developed by Xerox Corp along with DEC and Intel. It uses either a bus or star topology and supports data transfer rates of up to 10 mbps. Ethernet can connect devices in wired LAN or WAN.

An Ethernet card, also known as a network card, network adapter, or NIC (Network Interface Card), is a hardware device that facilitates the connection of nodes within a network. It enables computers to communicate over a computer network. It contains connections for either coaxial or twisted pair cables.

A hub is a multi-port and unintelligent network device that simply transfers data from one port of the network to another. It is a hardware device used to connect several computers together using different ports.

Active hubs electrically amplify the signal as it passes from one connected device to another. They are often used like repeaters to extend the length of a network. In contrast, passive hubs allow the signal to pass from one computer to another without any alteration or amplification.

Some services provided by a server on a network are:

1. Equipment/Resource Sharing — High quality printers and photocopiers are often designed to connect directly to a network and all authorised users can share the equipment. A server is responsible for such a resource sharing request.
2. Centralised File Saving for Data Sharing — Servers help the user save files to their home directories on the file server, workers can load their documents on any networked computer.
3. Centralised Virus Scanning — Most file servers run virus scanners constantly to detect and take care of viruses introduced by any user on any computer.
4. Centralised Backups — High-capacity tape devices in the file server back up all users' work, usually every night. In case of system failure (or worker failure), lost work can be recovered quickly and easily.

Fiber optic cable is recommended for very effective and fast communication in a guided medium.

In harsh industrial environments where there's a risk of extreme temperatures, moisture, chemicals, or physical damage, Fiber Optic cables must be used as they are immune to corrosion, water damage, and can withstand a wide range of temperatures.

Unguided media or wireless networking technology, such as microwaves, can effectively communicate over oceans.

Satellite transmission medium is useful for sparsely populated areas.

Mesh network topology is easy to expand.

Switch filters the data and router handles different protocol.

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

Major goals and applications of networks are :

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.
3. Reduced Costs — Since resources can be shared, it greatly reduces the costs.
4. Fast communication — With networks, it is possible to exchange information at very fast speeds.

Some advantages of optical fibres are:

1. It is immune to electrical and magnetic interference.
2. It is highly suitable for harsh industrial environments.
3. It guarantees secure transmission and has a very high transmission capacity.
4. Fiber optic cables can be used for broadband transmission.

Some disadvantages of optical fibres are:

1. Fiber optic cables are quite fragile and may need special care to make them sufficiently robust.
2. Connecting either two fibers together or a light source to a fiber is a difficult process.
3. In order to incept the signal, the fiber must be cut and a detector inserted.
4. Light can reach the receiver out of phase.
5. Connection losses are common problems.
6. They are more difficult to solder.
7. They are the most expensive of all the cables.

Some advantages of coaxial cables are:

1. The data transmission characteristics of coaxial cables are considerably better than that of twisted-pair cables.
2. They can be used as the basis for a shared cable network.
3. They can be used for broadband transmission.
4. They offer higher bandwidths — upto 400 Mbps.

Some disadvantages of coaxial cables are:

1. They are expensive as compared to twisted pair cables.
2. They are not compatible with twisted pair cable.

Some advantages of twisted pair cables are:

1. It is simple.
2. It is easy to install and maintain.
3. It is physically flexible.
4. It has a low weight.
5. It can be easily connected.
6. It is very inexpensive.

Some disadvantages of twisted pair cables are:

1. It is incapable of carrying a signal over long distances without the use of repeaters.
2. It is unsuitable for broadband applications due to its low bandwidth capabilities.
3. It supports maximum data rates of 1 Mbps without conditioning and 10 Mbps with conditioning.

Some advantages of radio waves are:

1. Its transmission offers mobility.
2. It proves cheaper than cables.
3. It offers freedom from land acquisition rights.
4. It offers ease of communication over difficult terrain.

Some disadvantages of radio waves are:

1. Communication is highly insecure.
2. Its propagation is susceptible to weather effects like rains, thunder storms etc.

Some advantages of micro waves are:

1. It proves cheaper than cables.
2. It offers freedom from land acquisition rights.
3. It offers ease of communication over difficult terrain.
4. Microwaves have the ability to communicate over oceans.

Some disadvantages of micro waves are:

1. It is an insecure communication.
2. Signals from a single antenna may split up and propagate by slightly different paths to the receiving antenna. When these out-of-phase signals recombine, they interfere, reducing the signal strength.
3. Its propagation is susceptable to weather effects like rains, thunder storm, etc.
4. Bandwidth allocation is extremely limited in case of microwaves.
5. The cost of design, implementation, and maintenance of microwave links is high.

Some advantages of satellites are:

1. The area coverage is quite large.
2. The laying and maintenance of intercontinental cable is difficult and expensive and this is where the satellite proves to be the best alterative.
3. The heavy usage of intercontinental traffic makes the satellite commercially attractive.
4. Satellites can cover large areas of the Earth. This is particularly useful for sparsely populated areas.

Some disadvantages of satellites are:

1. Technological limitations preventing the deployment of large, high gain antennas on the satellite platform.
2. Over-crowding of available bandwidths due to low antenna gains.
3. The high investment cost and insurance cost associated with significant probability of failure.
4. High atmospheric losses above 30 GHz limit carrier frequencies.

HTTP (Hypertext Transfer Protocol) is used to transfer all files and other data (collectively called resources) from one computer to another on the World Wide Web. This protocol is used to transfer hypertext documents over the Internet and defines how data is formatted and transmitted across the network. When an HTTP client (a browser) sends a request to an HTTP server (web server), the server responds by sending back data to the client.

A switch is a device that is used to segment networks into different sub-networks, called subnets or LAN segments to prevent traffic overloading.

A switch is responsible for filtering i.e., transforming data in a specific way and for forwarding packets between LAN segments. To insulate the transmission from the other ports, the switch establishes a temporary connection between source and destination and then terminates the connection once the conversation is done.

HTTP (Hypertext Transfer Protocol) is used to transfer all files and other data (collectively called resources) from one computer to another on the World Wide Web. This protocol is used to transfer hypertext documents over the Internet. HTTP defines how the data is formatted and transmitted over the network. When an HTTP client (a browser) sends a request to an HTTP server (web server), the server sends responses back to the client.

The main features of an HTTP protocol are:

1. It is a stateless protocol, this means that HTTP server need not keep track of any command and each command is independent of any other command.
2. It is an object-oriented protocol that uses the client server model.

The IP protocol deals only with packets, while TCP (Transmission Control Protocol) enables two hosts to establish a connection and exchange streams of data. TCP operates in conjunction with the Internet Protocol (IP), which defines how computers send packets of data to each other. These packets are initially delivered randomly, and TCP at the receiver side collects and arranges them in sequential order. IP is the primary protocol in the Internet layer of the Internet Protocol suite, responsible for delivering packets from the source host to the destination host based on the IP addresses mentioned in the packet headers, following the shortest route.

File Transfer Protocol is the simplest and most secure way to exchange files over the Internet. It is used to transfer files from server system to requesting node, primarily for information sharing. The main objectives of FTP are:

1. Indirect or implicit use of remote computers.
2. To shield a user from variations in file storage systems among different hosts.
3. To transfer data reliably and efficiently.
4. FTP uses the Internet's TCP/IP protocols to enable data transfer.

Hubs are preferred over repeaters when the distance between the terminals of the network is less and signals are not lost during transmission.

Bridges are preferred over hubs when we need to connect multiple networks.

We prefer switch over other network devices when we need to establish two-lane communication, facilitating send and receives at the same time. A switch provides full bandwidth to each connection and sends traffic only to appropriate connections, thus preventing traffic overload.

SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails across the Internet.

True

Reason — Protocol means a set of rules and regulations that governs a network. It represents the communication methods which are to be followed by the sending and receiving devices.

False

Reason — A repeater is a network device that amplifies a signal transmitted across the network, ensuring that the signal is received in the same way as it is sent. It operates at the physical layer of the OSI model and does not handle different protocols. On the other hand, a router operates at the network layer and is capable of handling different protocols.

False

Reason — A hub is known as an unintelligent device on the network that simply transfers data from one port of the network to another.

True

Reason — A website is a location on a web server where users can access and interact with digital assets (web pages, images, videos, audios etc) through a web browser.

True

Reason — A document that uses the HTTP (Hypertext Transfer Protocol) to be accessed and retrieved from a web server is called a web page.

False

Reason — A router is a device used to segment networks into sub-networks or subnets, while a switch is a network device used to interconnect computers or devices on a network.

False

Reason — Email helps us to send and receive messages through text using SMTP (Simple Mail Transfer Protocol) and POP3 (Post Office Protocol 3) protocols.

True

Reason — Attenuation refers to the weakening or loss of signal strength as it travels over a distance in a network or communication system. This can occur due to various factors such as resistance, interference, and absorption.

False

Reason — Optical fiber has higher tensile strength compared to coaxial cable due to the materials used in their construction, such as glass.

True

Reason — Secure communication refers to the process of exchanging information between two entities (such as individuals, devices, or systems) in a way that prevents unauthorized third parties from accessing or intercepting the communication.