11th Class (HSSC-I) Computer SLO Based Key Point Notes

(National Book Foundation - As Federal Textbook Board, Islamabad 
Based on National Curriculum Pakistan 2023-2024 and Onward prescribed by Federal Board of Intermediate and Secondary Education, Islamabad, and All Pakistan Boards) 
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Unit 5: Network Communication and Protocols


Q1. What is a Computer network?

Ans: 

A computer network is a  group of two or more computers linked together in order to share data and resources is known as a computer network. A network may be wired or wireless.

Q2. What is network communication and Name its basic component?

Ans: 

The process of transmitting data from one point to another over a network is known as network
communication. Its basic components are
● Sender     ●Medium     ●Receiver     ●Message     ●Protocol

Q3. Define network communication and its basic components. (Long-1)

Ans: 
The process of transmitting data from one point to another over a network is known as network communication. Its basic components are

● Sender     ●Medium     ●Receiver     ●Message     ●Protocol


Sender: The device that transmits data. It is also known as the encoder.

Medium: The mean which carries data physically from sender to receiver. It may be guided (wired) or unguided (wireless).

Receiver: The device that receives the data transmitted by the sender. It is also known as a decoder.

Message: The data which is transmitted from sender to receiver over a medium.

Protocols: The routines which govern the data communication are known as protocols. These are the software operating to carry out transmission securely.

Q4. Briefly describe the modes of network communication (Long-2)

Ans: 

There are five modes of data communication:
● Simplex     ●Half Duplex     ●Full Duplex     ●Synchronous     ● Asynchronous

The first three modes define the direction of communication and the other two define the style and speed of communication.

Simplex: In this mode, data can be transmitted only in one direction. It’s a one-way transmission mode in which the sender remains the sender and the receiver remains the receiver always. 
e.g. television and radio transmissions, data communication between computer and printer.


Half Duplex: In this mode, data can be transmitted in two directions but not simultaneously. It’s a two-way transmission mode in which the sender sends data at one time and can receive data at another time. 
e.g. walkie-talkies. Transactions between computer and credit card machine.


Full Duplex: In this mode, data can be transmitted in both directions at the same time. Both the sender and receiver can send and receive data at the same time. It’s the fastest mode. 
e.g. telephone conversation, computer network transmission.


Asynchronous Transmission: In this transmission, the time interval between any two consecutive characters is variable. Start and stop bits are used to show the starting and ending of the character. It’s a low cost and slower transmission as compared to synchronous mode. It is ideal for slow-speed transmission E.g. Keyboard data entry.


Synchronous Transmission: In this transmission, the time interval between any two consecutive characters is always the same. Two devices are synchronized before they start communication, and to remain synchronized, special idle characters are sent even if there is no data to send. It is more expensive but faster than asynchronous mode. E.g. transmission between devices in network communication links.



Q5. Differentiate between asynchronous and synchronous network transmission.

Ans: 

Asynchronous Transmission

Synchronous Transmission

The time interval between two consecutive characters is variable

The time interval between two consecutive characters is fixed

Start and Stop bits are sent with every character

Start and Stop bits are not sent

No idle characters are sent

Idle characters are sent if there is no data to send

Data is sent character by character

Data is sent block by block

It is slower

It is faster

It is a low-cost communication

It is expensive communication

The sender and receiver do not need to be synchronized

The sender and receiver need 
to be synchronized

Examples: Data communication by keyboard to the computer

Example: Transmission between devices in the network communication link

Q6. What are the advantages of using fiber optics?

Ans: 

  • It is the fastest medium i.e. data travels with the speed of light.
  • Suitable for long-distance communication.
  • Data communication is not affected by external factors like magnetic fields or temperature etc.

Q7. What is microwave transmission?

Ans: 

It is communication in the form of signals traveling in open space, like radio signals, Microwave systems are installed on high buildings or mountains to maintain line of sight to transmit or receive data. Long-distance microwave communication consists of relay stations (boosters) 30 miles apart, which amplify and retransmit data to other boosters.

Q8. What is satellite communication?

Ans: 

The communication carried out using satellites is known as satellite communication. The satellites are placed in the earth's orbits at a distance of 22000 miles above the surface of the earth. These satellites serve as a relay station between two earth-based stations.

Q9. Define Client and Server Computers

Ans: 

Server: A server is a computer that provides services to other computers. Generally, a server is a powerful computer having more resources than the client.

Client: The client is a computer that uses the services provided by the server computer. Generally, a client has fewer resources than a server.


Q10. Differentiate between server and client computer

Ans: 

Server Computer

Client Computer

The server is the computer that provides services

The client is the computer that receives services

The server controls and protects clients

Clients work under the control of the server

Servers are powerful computers

Clients are not powerful

Servers are fewer on a network

There are usually more clients on a network than servers.


Q11. Differentiate between client-server architecture.

Ans: 

Client Server Architecture

Peer-to-Peer Architecture

Each computer plays the role of client or server

Each computer is a client as well as a server at the same time

Clients work under the control of the server

No computer can control any other computer

It is a secure network

It is not secure

It may have more computers

It may have only two to ten computers

Only one user or group is the administrator of sharing data and resources

There are many administrators of sharing data and resources

Q12. Differentiate between LAN and WAN

Ans: 

Client Server Architecture

Peer-to-Peer Architecture

Each computer plays the role of client or server

Each computer is a client as well as a server at the same time

Clients work under the control of the server

No computer can control any other computer

It is a secure network

It is not secure

It may have more computers

It may have only two to ten computers

Only one user or group is the administrator of sharing data and resources

There are many administrators of sharing data and resources

Q14. What is a VPN?

Ans: 

A virtual Private Network is a secure network that allows easy and secure access to a private network using the Internet. For example, an employee can use his company network while he is traveling or in another city.


Q15. What is topology? name any four of its types.

Ans: 

The physical layout of computers over a network is known as topology. A topology defines the arrangement of computers on a network. The four topologies are

●Bus Topology     ●Star Topology     ●Ring Topology     ●Mesh Topology

Q16. Define Bus topology

Ans: 

Bus topology is a network layout in which all the computers are connected to a single cable known as a bus. When a computer wants to send data it sends it on a bus in both directions, each computer on the bus checks the address and copies the data if it matches, otherwise passes it on. Terminators at the end of the bus ground the data.



Q17. Define characteristics of Bus topology

Ans: 

  • Bus topology is the simplest topology.
  •  All computers are connected to a single cable known as a bus.
  • It’s a low-cost network.
  • Terminators are attached at each end to prevent the signal from reflecting back into the bus.
  • It is suitable for small networks.
  • Difficult to identify the problem if the whole network goes down.
  • It is easy to install and maintain.
  • If the cable is severed at any point or any of the computers is off, the whole network goes down.

Q18. Define Star topology

Ans: 

Star topology connects all the computers with a central networking device, hub, or switch. Every computer sends data to another computer via a hub/switch. It’s a flexible topology in which adding or removing of node is not an issue. 
Figure: Star Topology

Q19. Define the characteristics of Star topology

Ans: 

  • Star topology is a flexible topology.
  • All computers are connected to a central networking device, a switch, or a hub.
  • It’s an expensive network due to the use of a hub and extensive wiring.
  • Adding or removing computers is easy.
  • It is easy to install and maintain.
  • If the cable is severed at any point or any of the computers is off, the whole network does not go down.

Q20. Define Ring topology

Ans: 

Ring topology connects the computers in the form of an unbroken ring just like a bus having both ends brought together. The data travels in a single direction. It uses a token-passing technique in which the computer first sends the token to the destination node if it is acknowledged then data is transferred. 
Figure: Ring Topology

Q21. Define the characteristic of Ring topology.

Ans: 

  • Ring topology is in the form of an unbroken ring just like a bus having both ends brought together.
  • Adding or removing computers affects the whole network.
  • It implements a token-passing technique.
  • Data travels only in one direction.
  • The network may face reliability problems.
  • If the cable is severed at any point or any of the computers is off, the whole network goes down.


Q22. Define Mesh topology

Ans: 

Mesh topology connects each node to all the other nodes with dedicated links. It is a high-speed and the most reliable topology but is very difficult to install and modify.

Figure: Mesh Topology


Q23. Define the characteristic of Mesh topology

Ans: 

  • Each node is directly connected to all other nodes.
  • It is the most reliable network topology.
  • It can manage high-traffic data.
  • It is easy to troubleshoot.
  • It is the most expensive network.
  • It is difficult to install, maintain, and modify.

Q24. Differentiate between Bus and Star topologies.

Ans: 

Ring Topology

Star Topology

All computers are connected to a single wire forming an unbroken ring

All computers are connected to a central networking device known as a switch or hub

It is a slower network

It is faster

It is less expensive

It is expensive

It is suitable for small networks

It is suitable for small and medium-sized networks

If the cable is severed at any point or any of the computers are off, the whole network goes down

If the hub is off, the whole network goes down


Q25. Differentiate between Ring and Star topologies.

Ans: 

Bus Topology

Star Topology

All computers are connected to a single wire known as BUS

All computers are connected to a central networking device known as a switch or hub

It is a slower network

It is faster

It is less expensive

It is expensive

It is suitable for small networks

It is suitable for small and medium-sized networks

If the cable is severed at any point or any of the computers are off, the whole network goes down

If the hub is off, the whole network goes down

 

 

Q26. What is the OSI model?

Ans: 

ISO (International Standards Organization) developed standards for data communication at the national and international levels, OSI, Open System Interconnection, is the standard model for data communication systems developed by ISO in the 1970’s. OSI, consisting of seven layers, describes what happens when one terminal or computer talks to another. This model facilitates equipment from different vendors to communicate with each other.

Q27. Define all the layers of the OSI Model. (Long question)

Ans: 

OSI consists of seven layers. As discussed below


Application Layer: At this layer, software follows standards for look and feel. It serves the user as the user directly controls it. It’s where the network operating system and application software reside.

Presentation Layer: At this layer, data is formatted for viewing and for use on specific devices. This layer handles encryption and some special file formats. It formats screens and files so that the final output looks the way the programmer intended.

Session Layer: This layer provides a standard way to move data between application programs. It enables two applications or two parts of an application to communicate across the network providing security, name recognition, logging, administration, and other similar functions.

Transport Layer: The software at this layer provide for reliable and transparent transfer of packet between stations. It handles quality control by ensuring that the data received is in the right format and right order. It converts the data into packets at the sending end and opens them at the receiving end to see if anything is missing or broken. TCP works at this layer.

Network Layer: Software operating at this layer provides an interface between the physical + data link layers and the higher layers which establish and maintain connections. It decides which path should be followed to transmit data from one geographical point to another. It resides in switches and NICs. IP protocol works at this layer.

Datalink Layer: This layer provides for the reliable transfer of information across the physical layer. It synchronizes the blocks of data, recognizes errors, and controls the flow of data.

Physical Layer: The most important layer is concerned with transmitting a stream of data over the physical cables and wires. Hardware and software operating at this level deal with the types of connectors, signaling, and media-sharing schemes used on the network. It furnishes electrical connections for data transmission.

Note: Defining a separate single layer will become a short question


28. List the protocols working on each layer of the OSI Model.

Ans: 

Layer

Protocol

Application
Layer

HTTP

Presentation
Layer

Operating
System

Session
Layer

NetBIOS

Transport
Layer

TCP and UDP

Network
Layer

IP

Data Link
Layer

X.25 and IEEE 802.X

Physical
Layer

X.25 and  IEEE 802.X

 



29. Compare the TCP/IP model with the OSI model.

Ans: 

TCP/ IP Model

OSI Model

The TCP/IP model has four layers

OSI has seven layers

TCP/IP was developed by the US Department of Defense

OSI was developed by ISO in the early 1970’s

TCP/IP connects computers over the internet.

OSI serves as a gateway between the network and the end users

TCP/IP is a flexible model

OSI is strict to its protocols

TCP/IP revolves around internet communication

OSI is just a theoretical reference model

TCP/IP is a modern approach

OSI is the conventional approach

Its layers are Application, Transport, Network, Network interface

Its layers are Application, Presentation, Session, Transport, Network, Datalink, Physical

Q30. Define protocol

Ans: 

The routines which govern the data communication are known as protocols. These are the software operating to carry out transmission securely. Some popular protocols are HTTP, TCP, IP, X.25, and IEEE 802.X

Q31. Define TCP/IP.

Ans: 

TCP stands for Transmission Control Protocol and IP Stands for Internet Protocol. TCP/IP was developed by the US Department of Defense for communication over the Internet. These protocols became popular as they are the most efficient, reliable, and secure. TCP and IP work on the Transport and Network Layers of the OSI model, respectively.

Q32. Define UDP.

Ans: 

UDP stands for User Datagram Protocol. It works on the Transport layer as does the TCP, but the difference is that it does not ensure the security of data. It is faster than TCP but is not secure.


Q33. Define IEEE 802.X protocols

Ans: 

IEEE stands for Institute of Electrical and Electronics Engineers. 802 is the number of teams dealing with data communication and X denotes the protocol number it has developed, some popular IEEE 802.X protocols are 802.3, 802.5, 802.6

IEEE 802.3: This protocol deals with CSMA (Carrier Sense Multiple Access) signaling or Bus topology.

IEEE 802.5: This protocol deals with Token Ring Architecture, as implemented on ring topology.

IEEE 802.6: This protocol works on MAN (Metropolitan Area Network)

Q34. Define X.25 protocols

Ans: 

X.25 protocols define how communication devices (like routers) route data over connecting circuits. X.25 can be used over any satellite or ISDN (Integrated Services Digital Network). These are better known for their packet-switching capabilities. These are fast and extremely reliable.

 

Q35. Differentiate between circuit-switched and packet-switched network.

Ans: 

Circuit Switched Network

Packet Switched Network

There is a dedicated circuit connection between the sender and the receiver.

There is no dedicated connection.

The data to be sent is not divided into packets.

The data to be sent is divided into packets.

The message reaches the destination following a single route.

The message reaches the destination following multiple routes.

It is expensive.

It is less expensive.

It contains data of the same speed and the same type.

It contains the data of various types and speeds.


Q36. Briefly describe IP Addressing.

Ans: 

IP Address is a unique number that indicates a computer on the network or internet. Each computer on the Internet must have an IP address assigned by IANA, Internet Assigned Numbers Authority. IP Address consists of two parts Network Number and Host (computer) Number. There are 32 bits in an IP Address divided into 4 groups of eight bits each. Each group is known as an octet. 

Network Number

Computer Number


37. What are class A IP addresses?

Ans: 

Class A IP Address represents the largest networks. These are fewer in number. The First Octet denotes the network number and the next three denote the computer number. The distribution of 32 bits of an IP address is as:
The leftmost bit is always “0”, the next 7 bits identify the network number, which may be a total of 27 = 128, and the last 24 bits identify the computer number which is a total of 224 =16777216

0

1………………..7

8………….…………….31

10  

Network Number

Computer Number


Q38. What are class B IP addresses?

Ans: 

Class B IP Address represents medium-sized networks. The first two Octets denote the network numbers and the next two denote computer numbers. The distribution of 32 bits of the IP address is as:
The leftmost two bits are always “10”, the next 14 bits identify the network number, which may be a total of 214 = 16384, and the last 16 bits identify the computer number which is a total of 216 =65536

0-1

2………………..15

16………….…………….31

10  

Network Number

Computer Number


39. What are class C IP addresses?

Ans: 

Class C IP Address represents small networks, these are numerous. The first three Octets denote the network number and the last denotes the computer number. The distribution of 32 bits of the IP address is as:
The leftmost two bits are always “110”, the next 21 bits identify the network number, which may be a total of 221 = 4194304, and the last 8 bits identify the computer number which is a total of 28 =256

0-2

3………………..23

24………….…………….31

10  

Network Number

Computer Number

Q40. Define Subnet Mask

Ans: 

The subnet mask is used to identify which portion of the IP address identifies the network and which portion identifies the computer. The default subnet masks for Classes A,B, and C are as below:

Class A:  255.0.0.0
Class B:  255.255.0.0
Class C:  255.255.255.0  (Where 255 represents network and 0 represents computer)


Q41. What are communication devices? Define any three.

Ans: 

The devices used by telecommunication systems for transmitting data from one location to another are known as communication devices.

Hub: Hub is used to connect multiple computers together in a LAN. It receives data from one computer and broadcasts it to all computers.

Switch: Switch also connects multiple computers over a LAN-like hub, but it is more efficient and does not broadcast signals to all computers rather, sends them to the specified destination.

Router: Router connects two or more networks. When a computer sends a packet to a computer over the internet, the router receives it, looks for the nearest computer on the way, and decides the best pathway for network traffic.

Gateway: A Gateway is used to connect two networks that use different protocols. It changes the format of the data packet but not the contents of the message to make it conform to the application program of the remote computer.


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