Computer Network and Telecommunication

Networking and Telecommunication 

Communication 

Communication means sharing of ideas, view and information with other individuals or machine. 

Telecommunication 

Tele-communication is the process of communicating or transferring of data at a long distance. Some examples are telephone, radio, TV etc 

Data Communication 

The use of computer to send and receive the data from one place to another is known as data communication. Eg. E-Mail, Chat, and phone calls. 

Basic elements of data communication 

A sender: which creates the message to be transferred. 

A medium: which carries the message. 

A receiver: which receives the message. 

Data: instructions or information to be carried out

Protocols: rules to carry the data. 

Data Transmission Mode  

Data transmission mode is the way of transmission of data from one location to another. There are three types of transmission mode:

 i) Simplex mode

 ii) Half duplex mode 

iii) Full Duplex Mode 

Simplex mode  

Transmission of data takes place in only one direction. Devices connected to this mode either send or receive data at one time. For example radio, TV, Newspapers etc.  

Half duplex mode  

Data travels in both direction, but only one direction at a time. It can alternatively send or receive data. For example: Walkie-Talkie, pager, wireless handset. 

Full duplex mode  

Data travels in both directions simultaneously. Data can travel in both direction at a time.  For example: Telephone, Mobile, internet etc.  

Data transmission speed: 

The speed in which data can be transmitted form one device to another across a communication channel is called data transmission rate. It is measured in Kbps, Mbps, Gbps etc Some common terms used in communication media. 

BITS(Binary Digits): It is the smallest unit of the measurement of data in computer system. 

BANDWIDTH: it is the amount of data that can travel through a given transmission medium. We can measure bandwidth in digital devices by bits per second and in analogue devices by cycles per second or Hertz (Hz). 

Baud: A baud is the number of signals that changes per second. It specifies how fast the signals are changing in the communication. 

Media Connectors: 

It is a device through which various components of computer networks are connected. It is used to connect the computers in a network.  

Some of the connectors are: 

RJ-45 used in UTP cabling. 

BNC connector (British Naval Connector): used in co-axial cables ➢ ST connector: used in fiber optic 

Transmission medium / Communication Channel  

It is also called communication channel. A pathway for receiving and delivering data and information. The types of communication medium are:

• Guided Medium (Bounded or Wired) 
• Unguided Medium (Unbounded or Wireless

Guided medium 

The transmission media which uses cables or wires to transfer data and information among computers is called Guided media. They are called guided since they provide a physical channel from the sender device to the receiver device. E.g.: twisted pair cable, co-axial cable, fiber optics cable, etc. 

Features of guided media:  

Data transmits through the physical cable or fixed path 

Data transmission rate is higher. 

Guided VS Unguided Media 

Guided Media	Unguided Media
Guided media is a medium that sends signals through a solid physical path.	Unguided media is a medium that transmits signals through free space.
There is a specific direction to send signals.	There is no direction to send signals.
Used in wired transmission	Helps wireless transmission
Twisted pair, coaxial cable, and fiber optics	Radio wave, microwave, and infrared

Twisted pair cable 

A pair of wires twisted with each other is known as twisted pair cable. A set of four pairs of twisted wires are bundled to form cable. These are the most common medium for LAN. Wires are twisted with each other so as to reduce crosstalk (A disturbance caused by electromagnetic interference, along a circuit or a cable pair). Its types are: 

• Unshielded Twisted Pair Cable 
• Twisted Pair Cable 

Unshielded twisted pair (UTP) 

Unshielded twisted pair is a popular type of cable that consists of two unshielded wires twisted around each other which are used in telephone wiring and local area networks (LANs).

It is called unshielded because it has no additional foil wrap, or shield. 

RJ-45 connector is commonly used with unshielded twisted pair. 

Shielded twisted pair (STP) 

Shielded twisted pair is a type of copper telephone wiring in which each of the two copper wires are twisted together and coated with an insulating coating. 

The extra covering in shielded twisted pair wiring protects the transmission line from electromagnetic interference. 

D-shell connectors are used with shielded twisted pair. 

Co-axial cable 

Coaxial (or “coax”) cable is a common type of cable used for transmitting data over long distances. 

They are most used to transmit cable TV and Internet signals. 

The connectors used with co-axial cables are BNC, T-connectors, and terminators in bus topology. 

10 bps is the maximum speed of co-axial cable. 

Fiber optic cable 

Fiber optics cable is one of the costlier cables used in data communication which uses light to carry a data signal through the cable. 

The connectors used in fiber optics are Screw Mounted Adaptors (SMA), Springloaded Twist (ST), SC and FC. 

It is costlier to maintain, produce and install. 

Unguided media 

The transmission media which transfer data in the form of electromagnetic waves that do not require any cables for transmission is called unguided medium. These media are bounded by geographical boundaries. E.g.: radio wave, microwave, infrared etc. 

Radio wave transmission 

• The transmission making use of radio waves through air is called radio wave transmission. 
• It provides low bandwidth for data communication. Radio, TV, cellular phones etc. uses radio transmission in one form or another. 
• The radio waves can travel through walls and through an entire building. 
• Depending upon the frequency, they can travel long distance or short distance. 
• It does not require line of sight for data transmission 

Microwave transmission 

Microwave is a line-of-sight wireless communication technology that uses high frequency beams of radio waves to provide high speed wireless connections that can send and receive voice, video, and data information. 

• Microwaves do not pass through buildings. So, indoor receivers cannot be used effectively. 
• It provides higher bandwidth for data communication. 
• It requires line of sight for data transmission. 

Communication satellite 

• It is a artificial satellite used for wireless transmission of data. It is like microwave relay station in the sky. 
• The amplifier used to receive the information and retransmits signals sent from and earth station
  

Infrared transmission 

• Infrared Transmission is the transmission of data or voice information over infrared (IR) light over short ranges. It requires line-of-sight and is unable to break through walls. 

Bluetooth 

It is wireless medium that allow various device to communicate. It can transfer audio, video, or any multimedia contents. 

It is cost effective and better than infrared. 

It forms a PAN which does not require an internet connection. 

Works on radio waves (specially on the 2.4 GHz.) 

Wi-fi technology 

• Stands for Wireless Fidelity 
• Uses radio waves to provide network connectivity. 
• A wi-fi network is established using a wireless adapter to create hotspots areas in the area of a wireless router that is connected to the network allows users to access internet services. 
• Typically used to access internet on portable device like smartphone, tablets, or laptop 
• It provides access to a local network of connected device. 

Computer network  

The group of interconnected computers and other hardware by means of transmission media in order to communicate and share resources is known as computer network. 

Services provided by computer network. 

Print services: It include a sharing of printers. 

Message service: it includes sharing of message like e-mail. 

File service: it includes sharing of files. 

Application services: it includes sharing of application programs accessed by users. 

Database of services: it helps in managing, modifying, and distributing the data. 

Advantages of computer network 

• Hardware sharing 
• Data and software sharing 
• Cost effective. 
• Access to remote database 
• Increased storage capacity 
• Communicational facilities 

Disadvantages of computer network  

• Computer virus transfer 
• Less reliability 
• Loss of data 
• Need of skilled manpower 
• Cyber-crime may occur 

Components of computer network 

Client (workstation): Client means user. The computer where the client works is workstation. It requests or utilizes the resources of the server. Clients are the computer in which user run applications. 

Server: It is the main computer which response or provides services to other computers. It is a powerful computer having higher processing and storage capacity. Operating system like Linux, Unix, windows NT server, Novell NetWare etc. 

Types of server: 

Non dedicated server: 

it controls and provides services to the workstation as well as can be used as a workstation. For eg: windows NT server, Advanced 2000 server etc. are non-dedicated server. 

Dedicated server: 

It controls and provides services to the workstation but cannot be used as workstation. It is a powerful computer. For eg: Novell NetWare, Unix are dedicated server. 

NIC (Network Interface Card): It is a circuit board/interface card through which a computer is connected to the network. It is also known as Ethernet card. It helps to ensures reliable connection between workstation and server. 

Media connector: It is a device through which various components of computer networks are connected. It is used to connect the computer in a network. Some of connector are: 

Rj-45(Registered Jack) used in UTP cabling. 

ST Connector: used in fiber optic cable 

BNC (British Naval Connector): used in co-axial cable 

Types of computer network on the basis of geographical Location

LAN (Local Area Network) 

• It is limited to a small area. (Room, building, campus)
• It is faster than other type of network. 
• Coaxial or CAT 5 cables are normally used for connections. 
• It is limited to 10 km or less 
• Example: A computer network in a school. 

MAN (Metropolitan Area Network) 

• It covers entire city or district 
• It connects two or more LANs together 
•  It is limited to 100 KM or less. 
• Data transfer rate is low compared to LAN. 
• Example: Organization with different branches located in the city. 

WAN (Wide Area Network) 

• Extended to the whole world or universe. 
• Contains multiple LAN's and MAN's. 
• Distinguished in terms of geographical range. 
• Uses satellites and microwave relays. 
• Data transfer rate depends upon the ISP provider and varies over the location. 
• Best example is the internet. 

WLAN (Wireless LAN) 

A LAN that uses high frequency radio waves for communication. 

Provides short range connectivity with high speed data transmission. 

PAN (Personal Area Network) 

Network organized by the individual user for its personal use. 

SAN (Storage Area Network) 

Connects servers to data storage devices via fiber-optic cables. 

E.g.: Used for daily backup of organization or a mirror copy 

Node 

Each computer or device of network is called node. 

Router  

Router is an intelligent device that connects two different networks which uses the address for filtering and forwarding the data as well as it has an ability to determine the best route for destination. Cable 

Cables are commonly used media of physical channel for transmitting data between computers in network. 

Examples of cables are coaxial, twisted pair and fiber optic cable. 

Network topologies 

The physical layout or geographical orientation of a computer in network is known as network topology. 

 Bus topology: 

The type of arrangement of computers in which all the computers of network are connected to a single cable or trunk in a linear way is known as bus topology. 

Advantages 

• It is easy to setup. 
• It requires less no. of cable so it is not expensive. 
• It is easy to implement and extend. 
• Use of terminator doesn’t allow the data to escape 

Disadvantages 

• It depends on single cable. 
• Collision occurs. 
• It performance decreases when no. of computers are added. 
• It doesn't cover large geographical area. 
• Fault finding and troubleshooting is difficult. 

Ring Topology 

A computer arrangement in which all the computers or network are connected to a single cable or trunk in a circular way is known as ring topology 

Advantages 

• Increase of computer has minimal impact on performance. 
• All computer has equal access. 
• Each node on the ring has repeater, so it can be expanded to a greater distance. 
• Speed is high as data travel in only one direction. 

Disadvantages 

• It depends on single cable. 
• Adding and removing computers disturbs the whole network 
• Changing network structure is very difficult. 
• It cannot cover large geographical area. 
• Rewriting the program is required, while adding and removing the computer. 

Star Topology 

A topology in which all the computers and servers are connected to a centrally-located device called hub or switch in the form of star is known as star topology. 

Advantages 

• It is easy to add or remove computers in this topology. 
• If one computer or links fail, the other computer are not affected. 
• Computers can be added or remove easily without affecting the network. 
• It is one of the most reliable topologies. 

Disadvantages 

• It depends on central device, so if it fails the whole networks fails. 
• More number of cables or required 
• It is more expansive. 

Mesh Topology 

A topology in which all the computers are connected with one another forming a mesh is called mesh topology. It is the only true point to point design. This design is not very practical. 

Advantages 

• It is more reliable network. 
• Communication is faster between any two computers. 
• Fault finding and isolating is very easier. 

Disadvantages 

• It is difficult to install and reconfigure. 
• It is expensive as it uses maximum number of cables. 
• Because of complex nature it is not more popular or practical 

Network architecture (Models of Computer Network) 

Network model means How the computers are interacted and communicate in the network.  The arrangement of the computers on the network which is based on the computing model is called network architecture. Its types are

• Centralized computing network 
• Client / Server Network 
• Peer to Peer Network 

Centralized computing network 

• In these networks, all the workstation computers are connected to a center server computer, which acts as communicator among them. 
• A centralized computing network is a network in which a central host computer performs data processing and storage on behalf of clients.  
• All the services and management are responsible by central computer. 
• It is different from client server network as client server network consists of at least one server and one or more client as well as client server provides high security of data and other resources. 
• In this model entire computer depends on main computer.  
• Powerful operating system are used to handle data like Linux, Unix. 
• Workstation computers are used for input and output operations. 

Client/server network  

In this architecture, computer is connected to the device called server. Server control every client. The client has to request the server for the data. 

The server request, controls and response the client. The client utilizes the services provided by server.  

Advantage of Client server Architecture  

• It covers distance area(Large area) 
• It is more secure 
• It reduces traffic occur in Network. 
• It is more efficient types of network 

Disadvantage Client server N/W 

• Over load on server 
• Skilled manpower is needed for maintenance. 
• More expensive 
• If server fails, whole network will be disturbed. Peer-to-peer network  

Peer-to-Peer network

P2P is a group of computers, which function both as servers and workstations to share data, information and other resources of the network. In this type of architecture there is no dedicated server. Each of computer acts as both Client and server. It is less expensive but less efficient. All computers have equal responsibility. 

Advantages of peer to peer 

• Easy to setup 
• It is cheaper than Client-Server architecture. 
• Easy to troubleshoot. 
• All computer have equal rights. 
• It is suitable at home, office and small organization. 

Disadvantage of peer to peer 

• They are less secure than client-server model 
• The expansion of network is limited 
• It is slow because of heavy loads 
• It consumes more time to installed required S/W. 

Client/server network Vs Peer-to-peer network 

Client/server network	Peer-to-peer network
There is a specific server and specific clients connected to the server.	Clients and server are not distinguished, each node act as client and server.
It is secure network.	It is less secure.
It is more reliable.	It is less reliable.
Overload in server computer.	There is no dedicated server.
Client depends on server computer.	All the computers have equal responsibilities.
The data is stored in a centralized server.	Each peer has its own data.
The client-server is expensive to implement.	Peer-to-peer are less expensive to implement.

Internetworking device 

The devices that are used to connect two or more than two networks together are known as internetworking devices. For ex: Bridge, Router, Gateway, Repeater and so on. 

Repeater 

It is a network connecting device that increases the length of network by amplifying weak signals. It accepts weak signals, electrically regenerate them and again sends them on their way. 

Bridge   

It is a network connecting device that is used to join two similar types of networks or LANs together. 

Gateway 

This device is used to connect two dissimilar types of networks.  

HUB 

Hub is a device used to centralize network traffic via a single connecting point. It is also called multiport repeater. 

Switch  

This device connects two or more than two different networks. It is intelligent than Hub. 

Router 

It is also known as the intelligent device as it not only connects similar and dissimilar LANs together but also determines the best path for sending data to the receiver. 

Protocol 

A protocol is a set of rules that governs or control the transmission of data over a communication network. Some of common protocol. 

TCP/IP: Transmission Control Protocol/ Internet Protocol. It is responsible for verifying the correct delivery of data between the computers and internet. 

FTP: File transfer Protocol. It is responsible for transferring files or programs in the internet. 

HTTP: Hypertext Transfer Protocol. It is responsible for performing communication between web browsers and web server. 

SMTP: Simple mail Transfer Protocol. It is responsible for the transmission of e-mail message. 

POP: Post Office Protocol. It is responsible to retrieve email message from email server. 

ARP: Address Resolution Protocol. It is responsible for finding the hardware addressing of devices using IP address. 

IPX/SPX: Internetwork Packet eXchange / Sequenced Packet eXchange. 

Communication device 

This device transmits, translate and transform data into signals. For ex: MODEM and Multiplexors 

MODEM: Modulator Demodulator. It is a device which helps to translate the digital signal into analog signals and vice-versa. 

Multiplexor: it allows to send multiple signals across single transmission medium. Ex:  TV cable 

Internet and its services 

Internet 

• The largest network formed by connecting millions and billions of computers together all over the world is called internet.  It is also called network of networks. 
• Internet was first introduced by the department of defense of the USA as Advanced Research Project Agency (ARPA) in 1969. 
• In October 1st, 1997 first time, any message was sent ina network. 
• In Nepal Mercantile company started the internet service for the first time. 

Requirement to connect internet 

• Computer 
• ISP(internet service provider 
• A MODEM 
• Communication media 
• Web browser software 
• A telephone line ( in case of Dialup. 

Intranet 

It is a private computer network owned by a company or an organization. It is accessible only to the employees. It is generally used by private company, security departments like Nepal Police, Nepal Military Force, Home ministry and so on.  

Extranet: 

It is a computer that allows controlled access from the outside, for specific business or educational purpose. When two or more intranet is connected together to share its resources with the help of internet it forms Extranet.  

Internet	Intranet
1. It is a public network.	1. It is a private network.
2. It is not more secure.	2. It is more secure than Internet.
3. It run slower than intranet	3. It run faster than internet.

Services provided by internet 

Email 

Email stands for Electronic Mail. It is the way of sending and receiving mail  through internet. 

Email address: 

Email address is a unique address of different people in the internet. Basically, it has five parts: 

  

Comparison of Email and Postal Mail 

Email	Postal mail
It is very faster than postal mail It is more reliable Easy to send voice, image and other type of data Message can be receive from anywhere Email are more secure than postal mail It saves our time and money	it is very slower than email It is not reliable Difficult to send other type of data Message can be received only to the marked address. It is not secure It may takes a week, a month  or may be year

Newspaper (UseNet/newsgroup):  

It is a discussion group that focus on particular topic and helps in gathering information of related topic.  Anyone can post message at any time. The interested people can read or comment on the information. 

Telnet: 

It stands for Terminal Emulation Network. It is a service of the internet that allow a person to control a remote computer, so that the person can use from other location. 

File transfer: 

File can be transfer from client computer to the server computer and vice versa. It is provided by FTP. 

Internet Relay Chat: 

IRC is a online service of a internet. It allow people to send and receive text message or voice message in real time. 

Video conferencing: 

Video conferencing is a online service which enable face to face communication among the people sitting in different location virtually 

E-fax: 

It stands for Electronic- Fax. It is a service of internet that allows you to send and receive faxes directly on the computer. 

E-Commerce: 

It is a business in which you can sell and buy goods on the internet. It provides buying and selling facilities. Some of e-commerce sites of Nepal are: 

www.ipay.com 

www.Sastobazar.com 

www.kinmel.com.np 

www.muncha.com 

Internet telephony(VOIP-Voice Over Internet Protocol): 

It is a internet service that enables a user to make real time telephone communication 

Advertising  
Entertainment 
Online Shopping 

Internet related terms: 

Internet Service Provider(ISP): 

ISP is a company or organization that provide internet facilities to the people. Some of the ISP of Nepal are: Nepal Telecom (NTC), world link, Pokhara internet etc. 

Web browser: 

Web browser is a software program which are used to run internet and display webpage on the client computer. Some example are: Google Chrome, Mozilla Firefox, safari, Internet explorer, Opera etc. 

Web page: 

A web page is a electronic document written using HTML which consists of files that contain information of any organization, company, government agency etc. 

URL (Uniform Resource Locator): 

A URL is a unique address that provide location on the internet. It has four parts. i.e. protocol, server name, path, file name. 

Website:  

Website is a collection of Webpages. It contains main page/ index page called homepage and other subpages. 

Uploading and Downloading: 

Uploading is the process of copying user files, documents, program etc. to the server computer and downloading is the process of copying server files, documents, program etc. to the users computer. 

Domain name/type: 

• A domain name is the address where the internet users can access your website.  
• A domain name is used for finding and identifying computers on the internet.  
• The popular domain types are .com, .edu , .org , .net , .mil, etc. A domain name can be any combination of letters and numbers, and it can be used in combination of the various domain name extensions.  
• The domain name must be registered before you use it. Every domain name is unique.  

IP address: 

Internet Protocol address is an identifying number for network hardware that helps to connect to a network. 

• IP address allows a device to communicate with other devices. 
• An IP address provides an identity to a networked device on the internet.  
• There are two versions of IP and they are internet protocol version 4 (IPv4) and internet protocol version 6 (IPv6). 
• IPv6 is the upgraded IP version of IPv4.  

Blog (weblog) 

A blog is a time-stamped online journal that appears on a website. A blog is a frequently updated online personal journal or diary. A place to share your thoughts and your passions to the world. 

WWW (World Wide Web) 

The World Wide Web (abbreviated WWW or the Web) is an information space where documents and other web resources are identified by Uniform Resource Locators (URLs), interlinked by hypertext links, and can be accessed via the Internet. 

DNS (Domain Name System) 

Domain Name System is an Internet service that translates domain names into IP addresses.