Grade 12 Computer Science Note

Communication and Networking

Computer Network

It is defined as the collection of two or more autonomous computers which are interconnected together for sharing resources with the help of transmission media and set of protocols.

Advantages of Computer Network

  1. Sharing resources: hardware resources such as processor, storage devices, printers, scanner, etc. can be shared among us using computer network. It helps to minimize the operational cost of an organization.

  2. Faster and cheaper communication: communication in modern days has become very faster and cheaper to send information to a long distance through network.

  3. Centralized control: all network resources such as computers, printer file , database , etc can be managed and controlled by a central connecting computer also known as the server.

  4. Backup and recovery: server is used to keep data as backup. It maintains backup of all individual computer’s information.

  5. Remote and mobile access: a remote user can access resources from the distance using computer network.

Disadvantages of Computer Network

  1. Expensive: In order to install computer network, we require some extra cost to purchase networking devices such as hubs, switch, cables, etc.

  2. Security problems: network security is the most challenging job for network administrator in order to protect network resources from authorized users and physical destructions.

  3. Needs technical person: it is very difficult to install and operate good computer network.

 

Types of Computer Network

On the basis of size computer networks can be classified into three categories:

  1. Local Area Network (LAN): A LAN is privately owned small size network. It spans only in small geographical area such as within a room, office, buildings or up to few kilometers (2 to 3 Km). it connects the network resources such as computers, faxes, printers and various networking devices.

  2. Metropolitan Area Network (MAN): A MAN can be either public or privately owned network. Its size is bigger than LAN and smaller than WAN. It spans within one metropolitan city or larger geographical area. It can connect large number of computers and heterogeneous multiple LANs within a city maximum, up to 100Km.

  3. Wide Area Network (WAN): A WAN is basically public type heterogeneous network. It is the largest sized network and connects millions of computers, thousands of LANs, hundreds of MANs around the countries, continents and even the whole world.

 

Difference  between LAN and WAN

LAN

WAN

LAN (Local Area Network) is a computer network covering a small geographic area, like a home, office, school, or group of buildings.

WAN (Wide Area Network) is a computer network that covers a broad area (e.g., any network whose communications links cross metropolitan, regional, or national boundaries over a long distance).

High speed (1000 mbps)

Less speed (150 mbps)

Network in an organization can be a LAN

Internet is a good example of a WAN

If there is a need to set-up a couple of extra devices on the network, it is not very expensive to do that.

For WANs since networks in remote areas have to be connected the set-up costs are higher. However WANs using public networks can be setup very cheaply using just software (VPN etc).

LAN covers 100 m

WAN covers more than 100 m

Experiences fewer data transmission errors

Experiences more data transmission errors as compared to LAN

Typically owned, controlled, and managed by a single person or organization.

WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management over long distances.

 

 

Network topology and it's types

Network topology refers to the physical layout of the network. It shows the geometrical representation of all links and linking devices, also called nodes. Its types are as:

  1. Bus topology: computers are connected to a single continuous cable that is called bus. A bus must be terminated on both sides to prevent signal bounce and computers are connected to the bus with the help of drop line and T-connector.

  2. Star topology: Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

  3. Ring topology: In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

  4. Mesh topology: Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

  5. Tree topology: Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

  6. Hybrid topology: if two or more topologies are combined together then it is called hybrid topology. So it is very difficult to design and to implement the hybrid topology. It is expensive too.

 

Network architecture

Network architecture refers to the various services provided by the network and it also deals with how data is transmitted from one computer to others.

Client server network: The client/server topology is the model for vertical scaling, where clients typically host a small subset of the data in the application process space and delegate to the server system for the rest. Compared to peer-to-peer by itself, the client/server architecture provides better data isolation, high fetch performance, and more scalability. If you expect data distribution to put a very heavy load on the network, client/server architecture usually gives better performance. In any client/server installation, the server system is itself a peer-to-peer system, with data distributed between servers. Client systems have a connection pool, which it uses to communicate with servers and other Gem Fire members. A client may also contain a local cache.

Peer-peer network: The peer-to-peer distributed system is the building block for all Gem Fire installations. Peer-to-peer alone is the simplest topology. Each cache instance, or member, directly communicates with each every other member in the distributed system. This cache configuration is primarily designed for applications that want to embed a cache within the application process space and participate in a cluster. A typical application example would be an application server cluster where the application and the cache are co-located and share the same heap.

 

Difference  analog and digital single

Analog signal

Digital signal

Analog signal is a continuous signal which represents physical measurements.

Digital signals are discrete time signals generated by digital modulation.

Subjected to deterioration by noise during transmission and write/read cycle.

Can be noise-immune without deterioration during transmission and write/read cycle.

More likely to get affected reducing accuracy

Less affected since noise response are analog in nature

Stored in the form of wave signal

Stored in the form of binary bit

Low cost and portable

Cost is high and not easily portable

Example: Human voice in air, analog electronic devices.

Example: Computers, CDs, DVDs, and other digital electronic devices.

 

Difference between Internaet and Intranet

Internet

Intranet

The Internet is a worldwide, publicly accessible series of interconnected computer networks transmit data by packet switching using the standard Internet Protocol

An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organization's information or operations

This is the base, independent of the World Wide Web

Independent of the internet; however, internet is also used parallel

The Internet allows computer users to connect to other computers & information stores easily across the world; it is also used in marketing, online chat, file transfer, etc.

Intranets are being used to deliver tools & applications, helps to improve the services provided to the users, increases employees' ability to perform their jobs faster, etc.

Internet is a public computer network

Intranet is a private computer network

 

Signal modulation

In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal (high frequency signal), with a modulating signal that typically contains information to be transmitted.

Three forms of modulations are possible. They are as:

  1. Amplitude Modulation (AM): Amplitude modulation is an increase or decrease of the carrier voltage (Ec), will all other factors remaining constant.

  2. Frequency Modulation (FM): Frequency modulation is a change in the carrier frequency (fc) with all other factors remaining constant.

  3. Phase Modulation (PM): Phase modulation is a change in the carrier phase angle (θ). The phase angle cannot change without also affecting a change in frequency. Therefore, phase modulation is in reality a second form of frequency modulation.

 

Transmission media

A transmission media is defined as the means of communication between two networking devices that helps to transfer data from sender to receiver and vice versa.

Transmission media is broadly classified into two groups.

  1. Wired or Guided Media or Bound Transmission Media: Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.

  2. Wireless or Unguided Media or Unbound Transmission Media: Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. This type of transmission is called Wireless communication. Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra red are some of popular unbound transmission media.

 

Switching system

It provides a path between the two devices in a network. The process of transferring data blocks from one node to another node is called data switching.

Types of switching system are as follows:

  1. Circuit switching: It is the most familiar technique used to build a communication network. Used in ordinary telephone lines and it allows communications equipment and circuits to be shared among users. Each user has the sole access to a circuit during network use.

  2. Message switching: Message switching is a network switching technique in which data is routed in its entirety from the source node to the destination node, one hope at a time. During message routing, every intermediate switch in the network stores the whole message. If the entire network's resources are engaged or the network becomes blocked, the message-switched network stores and delays the message until ample resources become available for effective transmission of the message.

  3. Packet switching: A network technology that breaks up a message into small packets for transmission, unlike circuit switching, which requires the establishment of a dedicated point to point connections each packet in a packed switched network contains a destination address. Thus all packets in a single message do not have to follow the same path. Packet can arrive out of order. Destination computer reassembles the packets into their proper sequence.

 

OSI reference model

It is based on a proposal developed by the international organization for standardization (ISO). The model is called ISO OSI reference model, because it deals with connecting open system i.e. the system that are open for communication with other system.

1. Physical Layer: This layer concerned with transmission of bit it determines voltage level for 0 & 1. It also determines the data rate of the system. This layer involves standardized protocol dealing with electrical & signaling interface.

2. Data Link Layer: It handles error in physical layer. This layer ensures the correct delivery of frame to the destination address. It consists of 2 parts or 2 sub-layers. i.e.

  1. Logic Link Control

  2. Media Access Control

3. Network Layer: This layer is concerned with transmission of packet. N/w layer protocol chooses the best path to send a package called routing. Two protocols are widely used in n/w layer.

  1. X.25 Protocol

  2. Internet Protocol

4. Transport Layer: It provides the mechanism for the exchange of data between end systems. It ensures that the data received is in fact in order. Following jobs are performed by this layer.

  1. Port Addressing

  2. Segmentation & Reassemble

  3. Connection Control

5. Session Layer: It is responsible for requesting logical connection to be established for communication process. This logical connection is termed as session. It also provides data synchronization between two communication terminals.

6. Presentation layer: This layer translates format data to adapt to the needs of the application layer & nodes at both receiving & sending end of communication process. It handles data communication, formatting, encryption, decryption, etc.

7. Application Layer: It is the top-most layer of OSI model & provides user access to the n/w. It provides services that support user application, such as database access, email & file transfer, etc.

 

 

IP address: this is a code made up of numbers separated by three dots that identifies a particular computer on the Internet. Every computer, whether it is a Web server or the computer you're using right now, requires an IP address to connect to the Internet. IP addresses consist of four sets of numbers from 0 to 255, separated by three dots. For example "66.72.98.236" or "216.239.115.148". Your Internet Service Provider (ISP), will assign you either a static IP address (which is always the same) or a dynamic IP address, (which changes every time you log on).

MAC address: Stands for "Media Access Control Address," and no, it is not related Apple Macintosh computers. A MAC address is a hardware identification number that uniquely identifies each device on a network. The MAC address is manufactured into every network card, such as an Ethernet card or Wi-Fi card, and therefore cannot be changed.

Repeater: Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.

Bridge: In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).

Protocol: A standard set of regulations and requirements that allow two electronic items to connect to and exchange information with one another. Protocols regulate data transmission among devices as well as within a network of linked devices through both error control and specifying which data compression method to use. In particular, protocols decide: the method of error checking, how to compact data (if required), how the transmitting device signals that it has concluded sending data, and how the receiving device signals that it has completed receiving data.

Wi-Fi: Wi-Fi is the name of a popular wireless networking technology that uses radio waves to provide wireless high-speed Internet and network connections. A common misconception is that the term Wi-Fi is short for "wireless fidelity," however this is not the case. Wi-Fi is simply a trademarked phrase that means IEEE 802.11x.


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