Computer Networks - I

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
A standalone computer operates independently without being connected to a network, while a computer serving as a network node participates in network communication. To function as a network node, a computer requires a Network Interface Card (NIC) hardware, which facilitates communication over the network.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
A computer becomes a server when it possesses the capability to fulfill requests from other network nodes. This aligns with the definition of a server. Therefore, a server is a computer, but not all computers serve the same purpose.

(c)

Assertion is true but Reason is false.

Explanation
Users on a computer network interact with various network nodes such as computers, printers, switches, routers, etc., to access resources or services. In a computer network, a server is indeed considered a network node. A network node is any device connected to a network that can communicate with other devices. Servers, which provide services or resources to other devices on the network, are an integral part of network infrastructure and are thus considered network nodes.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
When a computer initiates a telephone call, the switching equipment within the telephone system seeks out a physical copper path all the way from sender telephone to the receiver's telephone. This establishes an end-to-end connection before any data transfer. A local telephone network provides an example of a circuit-switched network.

(c)

Assertion is true but Reason is false.

Explanation
In non-circuit switching techniques such as message switching and packet switching, messages may take different routes at different times. Message switching and packet switching are not the same techniques. In message switching, full message travel across different intermediate hops or switching offices, while packet switching involves dividing messages into packets and packets travel across hops.

(c)

Assertion is true but Reason is false.

Explanation
The tree topology is a hybrid topology created through a combination of Bus and Star topologies. In tree topology, transmission takes place in the same way as in the bus topology.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
Both the bus and star topologies are widely used in networking. The bus topology requires short cables and features a simple wiring layout. It provides a resilient architecture, which enhances hardware reliability. Therefore, the bus topology is considered as the simplest network topologies. While the star topology is known for its robustness, as it provides easy access for service and better fault tolerance compared to other topologies.

Two advantages of networks are:

1. It allows sharing of resources like printers, scanners.
2. It allows sharing of storage i.e., files can be shared over a network.

Two disadvantages of networks are:

1. If networks are badly managed, services can become unusable and productivity falls.
2. If software and files are held centrally, it may be impossible to carry out any work if the central server fails.

ARPAnet (Advanced Research Projects Agency NETwork) is regarded as the first computer network. It was started by the U.S. Department of Defense in 1969 with the goal of connecting the computers at different universities and U.S. defense. It laid the foundations of today's internet.

NSFnet was the high-capacity network started by the National Science Foundation which was more capable than ARPAnet. NSFnet allowed only academic research on its network and not any kind of private business on it.

InterSpace is a client/server software program that allows multiple users to communicate online with real-time audio, video and text chat in dynamic 3D environments.

A communication channel is a means of communication between two devices or workstations i.e., it refers to the medium used to carry information or data from one point to another. Communication channels can be grouped in two categories:

1. Guided media — These media include cables. There are three basic types of cables :
   1. Twisted-Pair Cables
   2. Coaxial Cables
   3. Fiber-optic Cables
2. Unguided media — These include waves through air, water or vacuum. Unsigned communication media are as follows:
   1. Microwaves
   2. Radiowaves
   3. Satellites

Baud is the unit of measurement for the information carrying capacity of a communication channel. It is synonymous with bps (bits per second).

bps refers to bits per second. It refers to the speed at which data transfer is measured. It is generally used to measure the speed of information through high speed phone lines or modems.

Bps refers to bytes per second.

All these terms are units of measurement for the information carrying capacity of a communication channel.

The types of network can be categorised based on geographical spread as well as component roles.

On the basis of geographical spread, networks can be of following types:

1. LAN (Local Area Network)
2. WAN (Wide Area Network)
3. PAN (Personal Area Network)
4. MAN (Metropolitan Area Network)

On the basis of component roles, networks can be of following types:

1. Client-server network
2. Peer-to-peer network

Some advantages of optical fibres are:

1. It is immune to electrical and magnetic interference.
2. It guarantees secure transmission and has a very high transmission capacity.

Some disadvantages of optical fibres are:

1. They are the most expensive of all the cables.
2. Connecting either two fibers together or a light source to a fiber is a difficult process.

Some advantages of satellites are:

1. The area coverage is quite large.
2. Satellites can cover large areas and are 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.

Some advantages of micro waves are:

1. It proves cheaper than cables.
2. It offers ease of communication over difficult terrain.

Some disadvantages of micro waves are:

1. It is an insecure communication.
2. Bandwidth allocation is extremely limited in case of microwaves.

Two disadvantages of twisted pair cables are:

1. It is incapable of carrying a signal over long distances without the use of repeaters due to high attenuation.
2. Its low bandwidth capabilities make it unsuitable for broadband applications.

An advantage of coaxial fiber cable is that it offers higher bandwidths of upto 400 Mbps.

A disadvantage of coaxial fiber cable is that it is expensive compared to twisted pair cables.

The pattern of interconnection of nodes in a network is called the Topology.

The most popular topologies are as follows:

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

The factors that must be considered before making a choice for the topology are as follows:

1. Cruciality of Work — How crucial the continuity of work is a very important factor. For instance, military networks must not fail at any cost thus fully connected topology is preferred for military networks.
2. Cost — Keeping in mind the budget, we should decide about a topology. A linear bus topology network may be the least expensive way to install a network. Fully connected is the most expensive way of creating a network.
3. Length of cable needed — Sometimes, length of cable must be saved. The linear bus topology network uses shorter lengths of cable.
4. Future growth — If a network has to grow in future, then the topology must support expansion. With a star topology, expanding a network is easily done by adding another concentrator.
5. Communication Media — Sometimes, difficult terrains like hilly areas do not allow use of regular cables. For such conditions, linear bus topologies are not possible. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

Similarities

1. Transmission can be done in both the directions, and can be received by all other stations.
2. There is no need to remove packets from the medium.

Differences

1. Tree topology is a network with the shape of an inverted tree with the central root branching and sub-branching to the extremities of the network whereas in bus topology, all devices on network are connected to a single continuous cable called a bus.
2. Tree topology is expensive and difficult to maintain as compared to Bus Topology.

The limitations of star topology are as follows:

1. A large quantity of cable is required to connect each node to the center.
2. It is difficult to expand.
3. If the central node in a star network fails, the entire network is rendered inoperable.

Ring topology becomes the best choice for a network when we need less connection of wires, have limited space and require very fast communication speed as optical fiber offers very high transmission speed in one direction.

The two advantages of bus topology in a network are:

1. It requires shorter cable length and has a simple wiring layout.
2. It provides a resilient architecture making it very reliable from a hardware point of view.

The two disadvantages of bus topology in a network are:

1. Fault diagnosis and isolation is difficult.
2. Reconfiguration is required when the network has its backbone extended using repeaters.

Two advantages of mesh topology are:

1. It provides extensive back-up and rerouting capabilities.
2. Each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.

Two disadvantages of mesh topology are:

1. Mesh networks can be complex to design, implement, and manage, especially as the number of nodes increases.
2. Maintenance and troubleshooting in mesh networks can be challenging due to their decentralized nature.

Two advantages of tree topology are:

1. It uses point-to-point wiring for individual segments.
2. It is supported by several hardware and software vendors.

Two disadvantages of tree topology are:

1. Overall length of each segment is limited by the type of cabling used.
2. If the backbone line breaks, the entire segment goes down.

The two advantages of bus topology in a network are:

1. It requires shorter cable length and has a simple wiring layout.
2. It provides a resilient architecture making it very reliable from a hardware point of view.

The two disadvantages of bus topology in a network are:

1. Fault diagnosis and isolation is difficult.
2. Reconfiguration is required when the network has its backbone extended using repeaters.

The types of addresses that play role in identifying a node on a network are as follows :

1. IP Address
2. MAC Address

(i) The name of logical address is IP address (Internet Protocol address).

(ii) The name of physical address is MAC address (Media Access Control address).

The size of a MAC address is 6-byte (48 bits).

A MAC address is a 6-byte address with each byte separated by a colon. The first three bytes (24 bits) of MAC address are the manufacturer-id or the Organisational Unique Identifier (OUI) (assigned to manufacturer by IEEE) and the last three bytes (24 bits) are the card-number (assigned by manufacturer). For example, a sample MAC address could be: 10 : B5 : 03 : 63 : 2E : FC. Here, 10 : B5 : 03 is the manufacturer-id and 63 : 2E : FC is the card number assigned by the manufacturer.

The two types of IP addresses are as follows:

1. Internet Protocol version 4 (IPv4) — It is a 4-byte (32 bit) address.
2. Internet Protocol version 6 (IPv6) — It is a 16-byte (128 bit) address.

The seeds of today's Internet were planted in 1969, when U.S. Department of Defense sponsored a project named ARPANET (Advanced Research Projects Agency NETwork). The goal of this project was to connect computers at different universities and U.S. defense. Soon the engineers, scientists, students and researchers, who were part of this system, began exchanging data and messages on it. The use­rs of this system were also able to play long distance games and socialize with people who shared their interests. ARPANET started with a handful of computers but it expanded rapidly.

In mid 80's, another federal agency, the National Science Foundation, created a new, high-capacity network called NSFnet, which was more capable than ARPANET. NSFnet allowed only the academic research on its network and not any kind of private business­ on it. So many private companies built their own networks, which were later interconnected along with ARPANET and NSFnet to form Internet.

It was the Inter networking i.e., the linking of these two and some other networks that was named Internet. The original ARPANET was shut down in 1990, and the government funding for NSF discontinued in 1995. But the commercial Internet services came into picture, which are running the Internet.

The Internet is a world-wide network of computer networks. In Internet, most computers are not connected directly to the Internet. Rather they are connected to smaller networks, which in turn are connected through gateways to the Internet backbone.

The Internet functions in the following way:

1. At the source computer, the message or the file/document to be sent to another computer is firstly divided into very small parts called packets. A packet generally contains some information.
2. Each packet is given a number serialwise e.g., 1, 2, 3.
3. All these packets are then sent to the address of destination computer.
4. The destination computer receives the packets in random manner. If a packet is garbled or lost, it is demanded again.
5. The packets are reassembled in the order of their number and the original message/file/document is obtained.

Based on geographical spread, networks can be of four types:

1. LAN (Local Area Network) — Small computer networks that are confined to a localised area such as a building or­ factory, are known as Local Area Networks (LANs). LANs have geographical spread of upto 1 km.
2. WAN (Wide Area Network) — The networks spread across countries or on a very big geographical area are known as WANs. The WANs link computers to facilitate fast and efficient exchange of information at lesser costs and higher speeds. The largest WAN in existence is the Internet.
3. PAN (Personal Area Network) — It is the interconnection of information technology devices within the­ range of an individual person, typically within a range of 10 meters. PAN could also be interconnected without wires to the Internet or other networks.
4. MAN (Metropolitan Area Network) — MAN refers to a network that is spread over an area as big as a city.

Based on component roles, network can be of two types:

1. Peer-to-Peer networks — Computers in peer-to-peer network can act as both servers sharing resources and as clients using the resources. A peer-to-peer network has upto ten computers.
2. Client/Server Networks — Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration. A client computer requests and utilizes network resources and a server is dedicated to processing client requests. Bigger networks prefer to have this type of network with centralized control.

LAN or Local Area Network refers to small computer networks that are confined to a localised area of upto 1 km. WAN or Wide Area Network refers to networks spread across countries or on a very big geographical area.

A Wide Area Network (WAN) can be a group of LANs that are spread across several locations and connected together to look like one big LAN. The WANs link computers to facilitate fast and efficient exchange of information at lesser costs and higher speeds.

The technique by which nodes of a network transmit data to other nodes, is known as switching technique.

The three switching techniques are as follows:

1. Circuit switching — A complete physical connection is established between the sender and the receiver and then data are transmitted from the source computer to the destination computer. A local telephone network is an example of a circuit-switched network.
2. Message switching — In this technique, the source computer sends message to the switching office first, which stores the data in its buffer. It then looks for a free link to another switching office and then sends the data to this office. This process is continued until the data are delivered to the destination computers. This working principle is known as store and forward i.e., store first, forward later, one jump at a time. Here full messages travel across different intermediate hops.
3. Packet switching — A fixed size of packet which can be transmitted across the network is specified. The message is divided into packets and packets travel across hops.

Communication media refer to the ways, means or channels of transmitting message from sender to the receiver.

Communication media can be grouped in two categories:

1. Guided media — These media include cables. There are three basic types of cables :
   1. Twisted-Pair Cables — These cables consist of two identical wires wrapped together in a double helix. These are also used for short and medium range telephone communication. The two types of twisted pair cables are Unshielded twisted pair cable (UTP) and Shielded twisted pair cable (STP).
   2. Coaxial Cables — This type of cable consists of a solid wire core surrounded by one or more foil or wire shields, each separated by some kind of plastic insulator. The inner core carries the signal, and the shield provides the ground. It is suitable for high speed communication. It is widely used for television signals. The two types of coaxial cables are thicknet and thinnet coaxial cable.
   3. Fiber-optic Cables — Optical fibres consist of thin strands of glass or glass like material which are so constructed that they carry light from a source at one end of the fiber to a detector at the other end. The fiber consists of core, cladding, protective coating. The bandwidth of the medium is very high. The two types of optical fibres are single mode and multimode fiber cables.
2. Unguided media — These media include waves through air, water or vacuum.
   Unguided communication media are as follows:
   1. Microwaves — The microwaves are similar to radio and television signals and are used for long distance communication. Microwave transmission consists of a transmitter, receiver and the atmosphere. The microwave transmission is line-of-sight transmission.
   2. Radiowaves — The transmission making use of radio frequencies is termed as radio-wave transmission. This transmission includes transmitter, receiver and antenna.
   3. Satellites — Satellite communication use the synchronous satellite to relay the radio signal transmitted from ground station. This transmission includes transponders.

Guided media include cables. There are three basic types of cables :

1. Twisted-Pair Cables — These cables consist of two identical wires wrapped together in a double helix. These are also used for short and medium range telephone communication. The two types of twisted pair cables are Unshielded twisted pair cable (UTP) and Shielded twisted pair cable (STP).
2. Coaxial Cables — This type of cable consists of a solid wire core surrounded by one or more foil or wire shields, each separated by some kind of plastic insulator. The inner core carries the signal, and the shield provides the ground. It is suitable for high speed communication. It is widely used for television signals. The two types of coaxial cables are thicknet and thinnet coaxial cable.
3. Fiber-optic Cables — Optical fibres consist of thin strands of glass or glass like material which are so constructed that they carry light from a source at one end of the fiber to a detector at the other end. The fiber consists of core, cladding, protective coating. The bandwidth of the medium is very high. The two types of optical fibres are single mode and multimode fiber cables.

Unguided media include waves through air, water or vacuum. Unguided communication media are as follows:

1. Microwaves — The microwaves are similar to radio and television signals and are used for long distance communication. Microwave transmission consists of a transmitter, receiver and the atmosphere. The microwave transmission is line-of-sight transmission.
2. Radiowaves — The transmission making use of radio frequencies is termed as radio-wave transmission. This transmission includes transmitter, receiver and antenna.
3. Satellites — Satellite communication use the synchronous satellite to relay the radio signal transmitted from ground station. This transmission includes transponders.

The different types of networks based on roles of computers are as follows :

1. Peer-to-Peer networks — Computers in peer-to-peer network can act as both servers sharing resources and as clients using the resources. A peer-to-peer network has upto ten computers.
2. Client/Server Networks — Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration. A client computer requests and utilizes network resources and a server is dedicated to processing client requests. Bigger networks prefer to have this type of network with centralized control.

The different types of networks based on geographical spread are as follows :

1. LAN (Local Area Network) — Small computer networks that are confined to a localised area such as a building or­ factory, are known as Local Area Networks (LANs). LANs have geographical spread of upto 1 km.
2. WAN (Wide Area Network) — The networks spread across countries or on a very big geographical area are known as WANs. The WANs link computers to facilitate fast and efficient exchange of information at lesser costs and higher speeds. The largest WAN in existence is the Internet.
3. PAN (Personal Area Network) — It is the interconnection of information technology devices within the­ range of an individual person, typically within a range of 10 meters. PAN could also be interconnected without wires to the Internet or other networks.
4. MAN (Metropolitan Area Network) — MAN refers to a network that is spread over an area as big as a city.

The patterns of interconnection of nodes in a network are called Topologies. Topology is important as it affects the choice of media and the access method used.

The types of topologies are as follows:

1. Star Topology — This topology consists of a central node to which all other nodes are connected by a single path.
   Advantages are :

   1. It provide easy access for service.
   2. Access protocols are very simple in star topology.
   3. There is a centralized control/problem diagnosis.
   4. Failure of single connection involves disconnecting only that node without affecting network.

   Disadvantages are :

   1. It requires long cable length.
   2. It is difficult to expand.
   3. There is a central node dependency.

2. Bus or Linear topology — This topology consists of a single length of the transmission medium onto which the various nodes are attached. Transmission from any station travels the length of the bus in both directions and can be received by all other stations. The destination device, on identifying the address on data packet copies the data onto its disk. When the data packet reaches at either end the terminator on that end absorbs the signal, removing it from the bus.
   Advantages :

   1. It requires short cable length and simple wiring layout.
   2. It provides resilient architecture.
   3. This topology can be expanded easily.

   Disadvantages :

   1. Fault diagnosis is difficult in this topology.
   2. Fault isolation is difficult in bus topology.
   3. Repeater configuration is necessary.
   4. Nodes must be intelligent in bus topology.

3. Tree Topology — This topology is combination of bus and star topologies. The shape of the network is that of an inverted tree with the central root branching and sub-branching to the extremities of the network. Transmission in this topology takes place in the same way as in bus topology.
   Advantages :

   1. It uses point-to-point wiring for individual segments.
   2. It is supported by several hardware and software vendors.
   3. It is flexible and scalable.

   Disadvantages :

   1. Overall length of each segment is limited by the type of cabling used.
   2. If the backbone line breaks, the entire segment goes down.
   3. It is more difficult to configure and wire than other topologies.

4. Ring or Circular Topology — In this topology, each node is connected to two and only two neighbouring nodes. Thus data travels in one direction only, from node to node around the ring. After passing through each node, it returns to the sending node, which removes it.
   Advantages :

   1. The chances of data collisions are low due to unidirectional flow of data.
   2. They are simple to design and implement.

   Disadvantages :

   1. Node failure breaks the ring and communication stops.
   2. Difficulty in troubleshooting.

5. Mesh topology — In this topology, each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.
   Advantages :

   1. It provides extensive back-up and rerouting capabilities.
   2. Each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.

   Disadvantages :

   1. Mesh networks can be complex to design, implement, and manage, especially as the number of nodes increases.
   2. Maintenance and troubleshooting in mesh networks can be challenging due to their decentralized nature.

6. Fully Connected topology — When in a network, there is a direct link between each host, then the network is said to be fully connected. This characteristic is termed as full connectivity.
   Advantages :

   1. Data travels quickly because devices are directly connected to each other.
   2. If one connection fails, there are other paths for communication to continue, making the network robust.

   Disadvantages :

   1. Managing all the connections can be complicated.
   2. Setting up and maintaining a fully connected network can be expensive.

In Internet, most computers are not connected directly to the Internet. Rather they are connected to smaller networks, which in turn are connected through gateways to the Internet backbone.

Internet functions in the following manner:

1. At the source computer, the message or the file/document to be sent to another computer is firstly divided into very small parts called packets.
2. Each packet is given a number serial wise e.g., 1, 2, 3.
3. All these packets are then sent to the address of destination computer.
4. The destination computer receives the packets in random manner. If a packet is garbled or lost, it is demanded again.
5. The packets are reassembled in the order of their number and the original message/file/document is obtained.

Every computer connected to the Internet uses communication protocols — Transmission Control Protocol(TCP) and Internet Protocol (IP).

a process in one device is able to exchange information with a process in another device

Reason — A computer network is a collection of interconnected autonomous computing device, so as to exchange information and­ share resources.

A computer that is not connected to a network

Reason — A computer that is not connected to a network is a stand alone computer.

Files cannot be shared between users

Reason — Files can be shared between users on the network.

Server

Reason — A computer that facilitates the sharing of data, software, and hardware resources on the network, is called a Server.

Increased security - user access to the network is controlled

Reason — The reason behind using a network over stand-alone computers is increased security through controlled user access.

peer-to-peer network

Reason — Network in which every computer is capable of playing the role of a client, or a server or both at same time is called peer-to-peer network.

A powerful computer that provides a service, such as centralised file storage

Reason — A server is a computer that provides services such as centralized file storage, data sharing, and access to software and hardware resources on the network.

peer

Reason — Each computer in P2P network controls its own information and plays role of either a client or a server depending upon what is needed at that point of time.

A LAN connects computers in a small area such as an office
A LAN can have geographical area up to 1 km

Reason — Small computer networks that are confined to a localised area upto 1 km (e.g., an office, a building or a factory) are known as Local Area Networks (LANs).

A school network

Reason — Wide Area Network (WAN) is a group of computers that are separated by large distances and tied together. While schools have Local Area Networks (LANs), these networks are confined to the school's premises.

Devices to be linked are mobile devices like laptops and smartphones spread over a large geographical area
Connecting devices keep moving from cities to countries

Reason — WLAN (Wireless local area network) is preferable when devices are mobile and spread over large areas, ensuring flexibility and continuous connectivity.

Devices to be linked are stationed within a small secluded place inside a city
Expenses to setup a network are limited

Reason — LAN is preferable when devices are stationary within a small area and expenses to setup the network should be kept lower.

Connecting devices are confined within a room
Connecting devices are within the range of same Wifi

Reason — A Personal Area Network (PAN) is the interconnection of information technology devices within the range of an individual person, typically up to 10 meters, e.g., using the same Wi-Fi network. Therefore, the above situations are suited for the use of PANs.

Circuit switching

Reason — In circuit switching technique, first an end-to-end path (connection) between computers is set up before any data can be sent. Therefore, this method offers a dedicated transmission channel.

Packet switching

Reason — In packet switching, packets are sent independently, allowing them to traverse various paths through the network to reach their destination.

Circuit switched

Reason — When we make a telephone call, the switching equipment within the telephone system seeks out a physical copper path all the way from the sender's telephone to the receiver's telephone. Hence, an end-to-end path is set up before any data can be sent. Therefore, a local telephone network is an example of a circuit-switched network.

Fibre optic

Reason — Optical fibers consist of thin strands of glass which are so constructed that they carry light from a source at one end of the fiber to a detector at the other end. Thus, the bandwidth of the medium is potentially very high.

Twisted pair cable

Reason — Twisted pair cable is the least expensive to manufacture.

Network Interface card

Reason — Each workstation needs an NIC (Network Interface card) to help establish a connection with the network because without this, the workstations will not be able to share network resources.

Fibre Optic

Reason — Fibre Optic is the fastest media of data transfer because the information travels on a modulated light beam.

distance of cable run
speed of transmission

Reason — Distance of cable run and speed of transmission should be considered when selecting the appropriate cable for connecting a PC to a network.

is less expensive than fiber
is easier to install than coaxial

Reason — Unshielded Twisted Pair Cable is less expensive than fiber optic cable and is easier to install than coaxial cable.

light

Reason — Fiber optics transmit data using light signals through optical fibers.

Radio-waves

Reason — Radio waves are unguided medium as they are waves through the air.

wireless transmission
unguided transmission

Reason — Radio waves, microwaves, and infrared waves are types of wireless transmission, also known as unguided transmission, because they propagate through the air or vacuum as waves.

guided transmission
wired transmission

Reason — Twisted-pair, coaxial, and fiber optic are types of wired transmission, also known as guided transmission, because they utilize cables.

allows longer distances
less effected by external signals

Reason — Optical fiber is immune to electrical and magnetic interference because the information is travelling on a modulated light beam. Hence, they allow long distance data transmission.

Network Topology

Reason — The pattern of interconnection of nodes in a network is called the network topology.

Star

Reason — Star topology consists of a central node to which all other nodes are connected by a single path.

Bus

Reason — Bus topology requires a multipoint connection on a single cable as it consists of a single length of transmission medium onto which the various nodes are attached.

Bus

Reason — Bus topology contains a backbone cable running through the whole length of the network to which all the nodes are attached.

Hub

Reason — A hub can be used at the centre of a star topology as it has multiple ports that are used for connecting multiple computers.

work unaffectedly

Reason — Star topology consists of a central node to which all other nodes are connected by a single path. Thus, failure of a single connection typically involves disconnection of one node from an otherwise fully functional network.

Tree

Reason — The shape of tree topology network is that of an inverted tree with the central root branching and sub-branching to the extremities of the network.

Bus

Reason — The internet operates on a bus topology where data flows through interconnected networks via a central backbone network.

Bus

Reason — Bus topology requires terminators at either end, which absorb the signal, to function correctly.

Star

Reason — Star topology uses hubs or switches as a central point of connection.

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.

In 1969, ARPANET was started by U.S. Department of Defense to connect computers at U.S. defense & different universities. In 1980s, the National Science Foundation started NSFnet to make a high capacity network to be used strictly for academic and engineering research.

In 1990s, many private companies built their own networks, which were later interconnected along with ARPANET and NSFnet to form Internet. Later, the commercial Internet services came into picture, which are running the Internet.

ARPAnet (Advanced Research Projects Agency NETwork) is regarded as the first computer network. It was started by the U.S. Department of Defense in 1969 with the goal of connecting the computers at different universities and U.S. defense. It laid the foundations of today's internet. The users of this system began exchanging data and messages on it. They were also able to play long distance games and socialize with people who shared their interests leading to its rapid expansion. The original ARPANET was shut down in 1990.

In Internet, most computers are not connected directly to the Internet. Rather they are connected to smaller networks, which in turn are connected through gateways to the Internet backbone.

Internet functions in the following manner:

1. At the source computer, the message or the file/document to be sent to another computer is firstly divided into very small parts called packets.
2. Each packet is given a number serial wise e.g., 1, 2, 3.
3. All these packets are then sent to the address of destination computer.
4. The destination computer receives the packets in random manner. If a packet is garbled or lost, it is demanded again.
5. The packets are reassembled in the order of their number and the original message/file/document is obtained.

Every computer connected to the internet uses communication protocols — Transmission Control Protocol(TCP) and Internet Protocol (IP).

InterSpace is a client/server software program that allows multiple users to communicate online with real-time audio, video and text chat in dynamic 3D environments. It provides the most advanced form of communication available on the Internet today.

The Interspace is a vision of what the Internet will become, where users cross-correlate information in multiple ways from multiple sources. It is an applications environment for interconnecting spaces to manipulate information.

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

The necessary network elements are :

1. Hosts/Nodes
2. Servers
3. Clients
4. Network hardware
5. Communication channel
6. Software
7. Network services

In circuit switching, a complete physical connection is established between the sender and the receiver and then data is transmitted from the source computer to the destination computer.

In message switching, no physical copper path is established in advance between sender and receiver. Instead when the sender has a block of data to be sent, it is stored in first switching office, then forwarded later, one jump at a time until the data is delivered to the destination computer. It works on the store and forward principle.

Switching techniques are used for­ transmitting data across networks. The switching techniques used are as follows:

1. Circuit switching — A complete physical connection is established between the sender and the receiver and then data are transmitted from the source computer to the destination computer.
2. Message switching — In this form of switching no physical copper path is established in advance between sender and receiver. Instead when the sender has a block of data to be sent, it is stored in first switching office, then forwarded later, one jump at a time until the data is delivered to the destination computer.
3. Packet switching — A fixed size of packet which can be transmitted across the network is specified. The message is divided into packets and packets travel across hops.

A communication channel is a means of communication between two devices or workstations i.e., it refers to the medium used to carry information or data from one point to another.

Communication channels can be grouped in two categories:

1. Guided media — These media include cables. There are three basic types of cables :
   1. Twisted-Pair Cables — These cables consist of two insulated copper wires twisted around each other. These are also used for short and medium range telephone communication.
   2. Coaxial Cables — A coaxial cable consists of one or more small cables in protective covering. These are more expensive than twisted pair cables but perform better.
   3. Fiber-optic Cables — These cables are made of plastic or glass and are about as thick as human hair. These cables are highly durable and offer excellent performance but are expensive.
2. Unguided media — These include waves through air, water or vacuum. Unguided communication media are as follows:
   1. Microwaves — The microwaves are similar to radio and television signals and are used for long distance communication. Microwave transmission consists of a transmitter, receiver and the atmosphere.
   2. Radiowaves — The transmission making use of radio frequencies is termed as radio-wave transmission.
   3. Satellites — Satellite communication use the synchronous satellite to relay the radio signal transmitted from ground station.

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.

The types of twisted pair cables are as follows :

1. Unshielded Twisted Pair (UTP) cable
2. Shielded Twisted Pair (STP) cable

The types of coaxial cables are as follows :

1. Thicknet coaxial cable
2. Thinnet coaxial cable

The types of fiber optic cables are as follows :

1. Single mode fiber cable
2. Multimode fiber cable

Bandwidth refers to the width of allocated band of frequencies to a channel. It is the difference between the highest and lowest frequencies of a transmission channel. Bandwidth is directly proportional to the amount of data transmitted or received per unit time.

In digital systems, bandwidth is data speed in bits per second (bps), bytes per second (Bps), mega bytes per second (MBps).

In analog systems, bandwidth is measured in cycles per second — kilohertz (kHz), megahertz (mHz), gigahertz (GHz) and terahertz (THz).

The data transfer rate represents the amount of data transferred per second by communications channel or a computing or storage device.

Data rate is measured in units of bits per second (bps), bytes per second (Bps), or baud.

For downloading: 56 kbps = 56,000 bits per second (1 kilo bit = 1000 bits)

For uploading: 14.4 kbps = 14,400 bits per second

So, the modem could download data at a rate of 56,000 bits per second and upload data at a rate of 14,400 bits per second.

Based on geographical spread, networks can be of four types:

1. LAN (Local Area Network) — Small computer networks that are confined to a localised area such as a building or­ factory, are known as Local Area Networks (LANs). LANs have geographical spread of upto 1 km.
2. WAN (Wide Area Network) — The networks spread across countries or on a very big geographical area are known as WANs. The WANs link computers to facilitate fast and efficient exchange of information at lesser costs and higher speeds. The largest WAN in existence is the Internet.
3. PAN (Personal Area Network) — It is the interconnection of information technology devices within the­ range of an individual person, typically within a range of 10 meters. PAN could also be interconnected without wires to the Internet or other networks.
4. MAN (Metropolitan Area Network) — MAN refers to a network that is spread over an area as big as a city.

Based on component roles, network can be of two types:

1. Peer-to-Peer networks — Computers in peer-to-peer network can act as both servers sharing resources and as clients using the resources. A peer-to-peer network has upto ten computers.
2. Client/Server Networks — Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration. A client computer requests and utilizes network resources and a server is dedicated to processing client requests. Bigger networks prefer to have this type of network with centralized control.

The network type that matches the given characteristics is the Personal Area Network (PAN).

The network type that matches the given characteristics is the Local Area Network (LAN).

The network type that matches the given characteristics is the Peer-to-Peer Network (P2P).

The network type that matches the given characteristics is the Wide Area Network (WAN).

The most used topologies are as follows:

1. Bus or Linear topology — In this topology, all devices on network are connected to a single continuous cable called a bus. Transmission from any station travels the length of the bus in both directions and can be received by all other stations. The destination device, on identifying the address on data packet copies the data onto its disk. When the data packet reaches at either end the terminator on that end absorbs the signal, removing it from the bus. This topology can be used for smaller networks.
2. Ring Topology — In this topology, each node is connected to two and only two neighbouring nodes. Data is accepted from one of the neighbouring nodes and is transmitted onwards to another. Thus data travels in one direction only, from node to node around the ring. After passing through each node, it returns to the sending node, which removes it.
3. Star Topology — In this topology each workstation is directly linked to a central node. Devices can be easily plugged or unplugged to the central node, as need dictates. Any communication between the stations must pass through the central node.
4. Tree Topology — In this topology the network is shaped as an inverted tree with the central root branching and sub-branching to the extremities of the network. Transmission in this topology takes place in the same way as in bus topology.
5. Mesh topology — In this topology, each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.
6. Fully Connected topology — When in a network each host is connected to other directly i.e., there is a direct link between each host, then the network is said to be fully connected. This characteristic is termed as full connectivity.

The factors that govern the selection of a topology for a network are as follows:

1. Cruciality of Work — How crucial the continuity of work is a very important factor. For instance, military networks must not fail at any cost thus fully connected topology is preferred for military networks.
2. Cost — Keeping in mind the budget, the topology should be decided based on cost. A linear bus topology network may be the least expensive way to install a network. Fully connected is the most expensive way of creating a network.
3. Length of cable needed — Sometimes, length of cable must be saved. The linear bus topology network uses shorter lengths of cable.
4. Future growth — If a network has to grow in future, then the topology must support expansion. With a star topology, expanding a network is easily done by adding another concentrator.
5. Communication Media — Sometimes, difficult terrains like hilly areas do not allow use of regular cables. For such conditions, linear bus topologies are not possible. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

False

Reason — A LAN is connected to a small geographical area, typically up to 1 km.

True

Reason — A client is a computer on the network that requests and utilizes network resources.

False

Reason — A computer is identified by 32 bit IP address (IPv4) and 128 bit IP address (IPv6).

True

Reason — Every object on the Internet, such as web pages, images, videos, documents, etc., typically has a unique URL (Uniform Resource Locator).

False

Reason — The term "host" refers to a computer connected to a network that seeks to share resources. A standalone computer cannot be used as a host because it is not connected to the network.

False

Reason — Peer-to-peer networks are small networks.

True

Reason — MAC address is a 48 bit address (6-byte).

False

Reason — Wide Area Network (WAN) is the largest network geographically because it spreads across countries or over a very large geographical area, encompassing multiple cities, countries, or continents.

False

Reason — Personal Area Network (PAN) is the smallest network geographically because it operates within the range of an individual person, typically up to 10 meters.

True

Reason — Personal Area Network (PAN) is the smallest network geographically because it operates within the range of an individual person, typically up to 10 meters.

True

Reason — A WAN covers a large geographical area across different locations. The internet spans the entire globe, connecting millions of networks and devices worldwide. Therefore, the Internet is an example of a Wide Area Network (WAN).

True

Reason — The bus topology requires short cables and features a simple wiring layout. It provides a resilient architecture, which enhances hardware reliability. Therefore, the bus topology is considered as the simplest network topologies.

True

Reason — In a star topology, each node is connected directly to a central node. If one node fails or its connection is disrupted, it only affects that individual node's connectivity. The rest of the network remains operational because the failure is contained within that specific node's connection.

False

Reason — The smallest network among LAN (Local Area Network), MAN (Metropolitan Area Network), and PAN (Personal Area Network) is PAN (Personal Area Network). PANs typically cover a very small area, usually within the range of 10 meters.

False

Reason — A network that includes a dedicated server is categorized as a client-server network. A dedicated server operates exclusively as a server within the network.

True

Reason — A network with a dedicated server is known as Master/Slave network or a client-server network. A dedicated server operates exclusively as a server within the network.

True

Reason — The first network was ARPANET (Advanced Research Projects Agency NETwork).

True

Reason — Initially, the Internet was formed by interconnecting ARPANET, NSFNet, and various university networks. This process of interconnecting these networks, along with others such as private networks, is known as inter networking, which eventually led to the creation of the Internet as we know it today.

False

Reason — Single mode fiber and multimode fiber are two types of fiber optic cables.

True

Reason — The two types of coaxial cables are thicknet and thinnet.

False

Reason — Single mode fiber and multimode fiber are the two types of fiber optic cables.

True

Reason — The two types of fiber optic cables are single mode fiber and multimode fiber.

True

Reason — UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair) are two types of twisted pair cables.