Unit 2 : Computer Networks
Introduction: A computer network is an interconnection among two or more computers or computing devices. Such interconnection allows computers to share data and resources among each other.
In a communication network, each device is called a node, that is a part of a network and that can receive, create, store or send data to different network routes.
A node can be a device such as a modem, hub, bridge, switch, router, a digital device or mobile, a printer, a computer or a server.
EVOLUTION OF NETWORKING
ARPANET – 1960
In the 1960s, the U.S. Department Of Defence had started a project named Advanced Research Projects Agency Network (ARPANET) to provide an interconnection between academic and research institutions for research purposes. They have started communication and the first message was communicated between the University of California, Los Angeles (UCLA) and Stanford Research Institute (SRI). Later on, other organizations had also joined ARPANET gradually and formed small networks.
Email – 1971
In 1971, Roy Romlinson develops a networking message popularly known as E-mail. With this, the symbol @ is used the first time with the network. Click here to read more about E-mail.
Internet – 1974
In 1974, the commercial use of ARPANET started in the name of TelNet. Later on, the word internet was coined. it also known as network of networks or WAN (Wide Area Network).
TCP/IP – 1982
By using the ARPANET project, now it is almost spread over countries with TelNet. In 1982 they have started using TCP/IP protocol in ARPANET. This protocol was developed by Robert Kahn and Vinton Cerf.
Domain Name System – 1983
In 1983, the Domain Name System was started. It was created by Paul Mockapetris in November 1983 to use some simple names rather than using the traditional addresses used in the ARPANET.
NSFNET – 1986
NSFNET program was launched by National Science Foundation in 1986 to bring connectivity to more people. It was popularly used to promote advanced research and education networking in the United States.
WWW – 1990
In 1990, Tim Berners Lee worked with European Organization for Nuclear research developed a program to make information readily available to users with different URLs and create relationships between websites, thus it gives birth to World Wide Web.
WiFi – 1997
In 1997, the first version of WiFi was introduced. Later on, so many changes and evolution took place and modern hi-speed internet came into the existence. WiFi is short for Wireless Fidelity.
Interspace
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.
an interspace is an advanced form of the internet where users communicate in multiple ways from multiple sources.
Internet vs. intranet vs. extranet
The internet is a global collection of computer networks known as the world wide web.
An intranet is an online network only company employees can access.
An extranet is an extension of an intranet. It lets approved third parties (such as vendors or customers) access restricted information.
Advantages / Need of a Computer Network:
1.Resource sharing : We can share hardware devices, softwares as well as data on a network.
2.Communication Medium : Network can provide communication between different computers attached to a network.
3.Reduced Cost : Sharing of resources helps in reducing hardware and software cost
4.Centralized Control: We can centrally control the computers attached to a network.
5.Central storage of data: We can save data of entire network on single computer. It helps in removing duplication of data as well as maintaining integrity of data.
Data Communication Terminologies
The term “Data Communication” comprises two words: Data and Communication. Data can be any text, image, audio, video, and multimedia files.
Communication is an act of sending or receiving data. Thus, data communication refers to the exchange of data between two or more networked or connected devices.
Main components of data communication
1. Message
This is the most valuable asset of a system for data communication. The message actually refers to data that is to be shared or a piece of information. A message is in any form, like a text file, an audio file, a video file, and so on.
2. Sender
Someone who can play the role of a source must be there to pass messages from source to destination. The sender plays a part of the data communication device root. A device that sends data messages is easy. The node can be a computer, mobile device, telephone, laptop, video camera, workstation, etc.
3. Receiver
It is the destination where messages sent by the source have finally arrived. It is a message-receiving system. The receiver is in the form of a computer, cell phone, workstation, etc., identical to the sender.
4. Transmission Medium / Communication Channel
There must be something in the entire data communication process that could act as a bridge between sender and receiver. The transmission is the physical path from the sender to the recipient where the information or message passes.
The examples of transmission medium are twisted pair cable, fibre optic cable, radio waves, microwaves, etc. The transmission medium could be guided (with wires) or unguided (without wires).
5. Protocol
Different sets of rules have already been designed by the designers of communication systems to control data communication, reflecting a sort of agreement between communicating devices. These are characterized as protocols.
The protocol is also called as a set of rules regulating data communication. If two separate devices are connected, but there is no protocol between them, there will be no contact between the two devices of any sort.
MEASURING CAPACITY OF COMMUNICATION MEDIA
In data communication, the transmission medium is also known as channel. The capacity of a channel is the maximum amount of signals or traffic that a channel can carry. It is measured in terms of bandwidth and data transfer rate .
Bandwidth:
Bandwidth of a channel is the range of frequencies available for transmission of data through that channel. Higher the bandwidth, higher the data transfer rate. Normally, bandwidth is the difference of maximum and minimum frequency contained in the composite signals. Bandwidth is measured in Hertz (Hz). 1 KHz =1000 Hz 1 MHz =1000 KHz = 1000000 Hz
Data Transfer Rate:
Data travels in the form of signals over a channel. One signal carries one or more bits over the channel. Data transfer rate is the number of bits transmitted between source and destination in one second. It is also known as bit rate. It is measured in terms of bits per second (bps).
The higher units for data transfer rates are:
1 Kbps=1024 bps
1 Mbps=1024 Kbps
1 Gbps=1024 Mbps
1 Tbps=1024 Gbps
Types of Data Communication
Data communication happens in the form of signals between two or more computing devices or nodes. The transfer of data happens over a point-to-point
or multipoint communication channel.
Data communication between different devices are of 3 types:
- Simplex communication,
- Half-duplex communication
- Full-duplex communication.
1. Simplex Communication
It is a one way or unidirectional communication between two devices in which one device is sender and other one is receiver. Devices use the entire capacity of the link to transmit the data. It is like a one way street where vehicles can move in only one direction.
For example, data entered through a keyboard or audio sent to a speaker are one way communications.
2. Half-duplex Communication
It is two way or bidirectional communication between two devices in which both the devices can send and receive data or control signals in both directions, but not at the same time. While one device is sending data, the other one will receive and vice-versa.
It is like sharing a one-way narrow bridge among vehicles moving in both directions. Vehicles cannot pass the bridge simultaneously. Basically, it is a simplex channel where the direction of transmission can be switched.
Application of such type of communication can be found in walkie-talkie where one can press the push-to-talk button and talk. This enables the transmitter and turns off the receiver in that device and others can only listen.
3. Full-duplex Communication
It is two way or bidirectional communication in which both devices can send and receive data simultaneously. It is like a two way road where vehicles can go in both directions at the same time.
for example, in our mobile phones and landline telephones.
Switching Techniques
In a network having multiple devices, we are interested to know how to connect the sender and receiver so that one-to-one communication is possible.
for this we can use a technique of switching whereby data is routed through various nodes in a network. This switching process forms a temporary route for the data to be transmitted. Two commonly used switching techniques are — Circuit Switching and Packet Switching.
1. Circuit Switching
In circuit switching, before a communication starts, a dedicated path is identified between the sender and the receiver. This path is a connected sequence of links
between network nodes. All packets follow the same path established during the connection.
In earlier days, when we placed a telephone call, the switching equipment within the telephone system finds out a physical path or channel all the way from our telephone at home to the receiver’s telephone. This is an example of circuit switching.
2. Packet Switching
In packet switching, each information or message to be transmitted between sender and receiver is broken down into smaller pieces, called packets. These packets are then transmitted independently through the network. Different packets of the same message may take different routes depending on availability.
Each packet has two parts — a header containing the address of the destination and other information, and the main message part. When all the packets reach
the destination, they are reassembled and the complete message is received by the receiver.
Unlike circuit switching, a channel is occupied in packet switching only during the transmission of the packet. On completion of the transmission, the channel is available for transfer of packets from other communicating parties.
IDENTIFYING NODES IN A NETWORKED COMMUNICATION
Each node in a network should be uniquely identified so that a network device can identify the sender and receiver and decide a routing path to transmit data.
Let us explore further and know how each node is distinguished in a network.
MAC Address
MAC stands for Media Access Control. The MAC address, also known as the physical or hardware address, is a unique value associated with a network adapter called a NIC. The MAC address is engraved on NIC at the time of manufacturing and thus it is a permanent address and cannot be changed under any circumstances. The machine on which the NIC is attached, can be physically identified on the network using its MAC address.
Each MAC address is a 12-digit hexadecimal numbers (48 bits in length), of which the first six digits (24 bits) contain the manufacturer’s ID called Organisational Unique Identifier (OUI) and the later six digits (24 bits) represents the serial number assigned to the card by the manufacturer. A sample MAC address looks like:
IP Address
IP address, also known as Internet Protocol address, is also a unique address that can be used to uniquely identify each node in a network. The IP addresses are assigned to each node in a network that uses the Internet Protocol for communication. Thus, if we know a computer’s IP address, we can communicate with that computer from anywhere in the world. However, unlike MAC address, IP address can change if a node is removed from one network and connected to another network.
The initial IP Address called version 4 (IPV4 in short), is a 32 bit numeric address, written as four numbers separated by dots, where each number is the decimal (base-10) representation for an 8-bit binary (base-2) number and each can take any value from 0 - 255.
A sample IPV4 address looks like: 192:168:0:178
With more and more devices getting connected to the Internet, it was realised that the 32-bit IP address will not be sufficient as it offers just under 4.3 billion unique addresses. Thus, a 128 bits IP address, called IP version 6 (IPV6 in short) was proposed. An IPv6 address is represented by eight groups of hexadecimal (base-16) numbers separated by colons.
A sample IPV6 address looks like:
2001:CDBA:0000:0000:0000:0000:3257:9652
DOMAIN NAME SYSTEM
The Internet is a vast ocean where information is available in the form of millions of websites. Each website is stored on a server which is connected to the Internet,
which means each server has an IP address. Every device connected to the Internet has an IP address. To access a website, we need to enter its IP address on our web browser. But it is very difficult to remember the IP addresses of different websites as they are in terms of numbers or strings.
However, it is easier to remember names, and therefore, each computer server hosting a website or web resource is given a name against its IP address.
These names are called the Domain names or hostnames corresponding to unique IP addresses assigned to each server. For easy understanding, it can be considered as the phonebook where instead of remembering each person’s phone number, we assign names to their numbers. For example, IP addresses and domain names of some websites are as follows:
DNS Server
Instead of remembering IP addresses, we assign a domain name to each IP. But, to access a web resource, a browser needs to find out the IP address corresponding to the domain name entered. Conversion of the domain name of each web server to its corresponding IP address is called domain name resolution. It is done through a server called DNS server.
Thus, when we enter a URL on a web browser, the HTTP protocol approaches a computer server called DNS server to obtain the IP address corresponding to that domain name. After getting the IP address, the HTTP protocol retrieves the information and loads it in our browser.
An example is shown in which the HTTP requests a DNS server for corresponding IP addss, and the server sends back an IP address.
A DNS server maintains a database of domain names and their corresponding IP addresses. To understand how the domain name resolution works, we have to
understand how and where the DNS servers are kept.
The DNS servers are placed in hierarchical order. At the top level, there are 13 servers called root servers. Then below the root servers there are other DNS servers at different levels. A DNS server may contain the IP address corresponding to a domain or it will contain the IP address of other DNS servers, where this domain entry can be searched.
Note: DNS root servers are named using alphabets A through M for the first 13 letters of the alphabet. Ten of these servers are in the US, one in London, one in
Stockholm, and one in Japan. The organisation Internet Assigned Numbers Authority (IANA) keeps this list of DNS root servers.
Transmission Media
A transmission medium can be anything that can carry signals or data between the source (transmitter) and destination (receiver). For example, as we switch on a ceiling fan or a light bulb, the electric wire is the medium that carries electric current from switch to the fan or bulb.
In data communication, transmission media are the links that carry messages between two or
more communicating devices. Transmission can be classified as guided or unguided.
In guided transmission, there is a physical link made of wire/cable through which data in terms of signals are propagated between the nodes. These are usually metallic cable, fiber-optic cable, etc. They are also known as wired media.
In unguided transmission, data travels in air in terms of electromagnetic waves using an antenna. They are also known as wireless media.
Wired / Guided/ Bound Transmission Media
Any physical link that can carry data in the form of signals belongs to the category of wired transmission media. Three commonly used guided/wired media for data transmission are, twisted pair, coaxial cable, and fiber optic cable. Twisted-pair and coaxial cable carry the electric signals whereas the optical fiber cable carries the light signals.
1. Twisted Pair Cable
These cables consist of two insulated copper wires twisted around each other in a double helix. Twisting of wires reduces crosstalk which is bleeding of a signal from one wire to another.
Types:
- Unshielded Twisted Pair (UTP)
- Shielded Twisted Pair (STP)
STP offers greater protection from interference and crosstalk due to shielding.
But it is heavier and costlier than UTP.
USE :
- In local telephone communication
- For digital data transmission over short distances upto 1 km
Advantages:
- Easy to install and maintain
- Simple
- Inexpensive
- Low weight
- Suitable for small (Local) Networks
Disadvantages:
- Not suitable for long distance due to high attenuation.
- Low bandwidth support.
- Low Speed
2. Coaxial cable
Coaxial cable consists of a solid copper wire core surrounded by a plastic cladding shielded in a wire mesh. Shield prevents the noise by redirecting it to ground.
Types:
Coaxial cable comes in two sizes which are called thinnet and thicknet.
Thicknet : segment length upto 500 m
Thinnet : segment length upto 185 m
USE:
In TV channel communication
Advantages:
- Better than twisted wire cable.
- Popular for TV networks.
- Offers higher bandwidth & Speed
Disadvantages:
- Expensive than twisted wires.
- Not compatible with twisted wire cable.
3. Optical Fibre Cable (OFC)
Thin strands of glass or glass like material designed to carry light from one source to another. Source converts (Modulates) the data signal into light using LED (Light Emitting Diodes) or LASER diodes and send it over the Optical fiber.
It consists of three parts:
- The core: glass or plastic through which the light travels.
- The cladding : covers the core and reflects light back to the core
- Protective coating : protects the fiber
Advantages:
- Not affected by any kind of noise.
- High transmission capacity
- Speed of Light
- Suitable for broadband communication
Disadvantages:
- Installation requires care.
- Connecting two Optical fibers is difficult.
- Optical fibers are more difficult to solder
- Most expensive
Wireless / unguided/ unbound Transmission Media
1. Microwaves
Microwaves are transmitted from the transmitters placed at very high towers to the receivers at a long distance. Microwaves are transmitted in line of sight fashion, and also propagated through the surfaces.
Main points:
1. Electromagnetic waves of frequency range 1GHz - 300GHz.
2. Unidirectional, can move in only one direction.
3. Cannot penetrate solid objects such as walls, hills or mountains.
4. Needs line-of-sight propagation i.e. both communicating antenna must be in the
direction of each other.
5. Used in point-to-point communication or unicast communication such as radar
and satellite.
6. Provide very large information-carrying capacity.
Advantages:
- Maintenance easy than cables.
- Suitable when cable can not be used.
- Cheaper than cables
- Land is required to fix towers only, saves the space of land to spread the cables
- It can provide easy communication over difficult terrain
- It can communicate over oceans
Disadvantages:
- Repeaters are required for long distance communication.
- Less Bandwidth available
- Insecure connection
- The network can be affected by weather effects such as rains, thunderstorms etc.
- Limited bandwidth
- Very high-cost maintenance
2. Radiowaves
It is using the radio frequency modulation for data transmission. It has two parts:
- Transmitter – take data or message, encode it into sine wave and transmit into a radio wave
- Receiver – decodes the data or message from sine wave it receives
In radio wave both transmitter and receiver antennas to radiate and capture the radio signal.
Main Points:
- Waves of frequency range 3 KHz - 1 GHz
- Omni-directional, these waves can move in all directions
- Radio waves of frequency 300KHz-30MHz can travel long distance
- Susceptible to interference
- Radio waves of frequency 3-300KHz can penetrate walls
- These waves are used in AM and FM radio, television, cordless phones
The advantages and disadvantages are similar as micro wave.
3. Infrared waves
The electromagnetic waves having frequencies from 300 GHz to 400 THz (wavelengths from 1mm to 770 nm) are referred to as infrared (IR) waves. IR uses line-of-sight propagation.
Infrared light is a transmission channel whose features are necessarily different from those of the radio frequencies. A fundamental property of infrared light is that it cannot penetrate the walls. This represents that it can easily include it within a room.
Main points:
1. Electromagnetic waves of frequency range 300GHz - 400THz.
2. Very high frequency waves.
3. Cannot penetrate solid objects such as walls.
4. Used for short-distance point-to-point communication such as mobile to mobile,
mobile-to-printer, remote-control-to-TV, and Bluetooth enabled devices to other
devices like mouse, keyboards etc.
Advantages:
- It is a very high speed transmission.
- It has a large bandwidth.
- It is very cheap.
- It can be simple to create.
- It provides a wireless connection between two systems.
- There is no license needed to facilitate it.
Disadvantages:
- It cannot permeate the barrier.
- It cannot use it for long-range communication.
Satellite Communication
A satellite is an object that revolves around another object. For example, earth is a satellite of The Sun, and moon is a satellite of earth.
A communication satellite is a microwave repeater station in a space that is used for telecommunication, radio and television signals. A communication satellite processes the data coming from one earth station and it converts the data into another form and send it to the second earth station.
How a Satellite Works
Two stations on earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a relay station for their communication. One earth station transmits the signal to the satellite.
Uplink frequency is the frequency at which ground station is communicating with satellite. The satellite transponder converts the signal and sends it down to the second earth station, and this is called Downlink frequency. The second earth station also communicates with the first one in the same way.
Advantages of Satellite:
- The Coverage area is very high than that of terrestrial systems.
- The transmission cost is independent of the coverage area.
- Higher bandwidths are possible.
Disadvantages of Satellite:
- Launching satellites into orbits is a costly process.
- The bandwidths are gradually used up.
- High propagation delay for satellite systems than the conventional terrestrial systems.
Network Devices:
To communicate data through different transmission media and to configure networks with different functionality, we require different devices like Modem, Hub, Switch, Repeater, Router, Gateway, etc.
NIC (Network Interface card) :-
It is a device attached to each workstation and server. Helps to make connections within the network.
Each NIC has a unique number identifying it called node address/MAC address (Media Access Control) /Physical Address.
Types:
- Ethernet Card
- WiFi Card
MODEM (Modulator - Demodulator) :-
- The modem is an abbreviation for Modulator – Demodulator.
- The modulator converts information from digital mode to analog mode at the transmitting end and the demodulator converts the same from analog to digital at receiving end.
RJ - 45 -:
- RJ-45 stands for Registered Jack-45.
- RJ-45 is an eight-wire connector, which is commonly used to connect computers on LAN especially Ethernet.
REPEATER :-
- It is a device that accepts the weak signals and amplifies the signals for further transmission.
- Different types of wires have different transmission distances, hence repeater should be used according to the types of wire.
- Generally, we consider that most wires require a repeater after a 100m distance.
HUB :-
- Hub is an electronic device that connects several nodes to form a network and redirect the received information to all the nodes in a broadcast mode. It is called a non-intelligent device.
- It is mostly used in Star or Ring topology and works on MAC addresses.
- Active hub:- electrically amplify the signal.
- Passive hub:- do not amplify the data.
SWITCH :-
- It is an intelligent device that connects several nodes to form a network and redirect the received information only to the intended node(s).
- A switch is also called Intelligent HUB.
- Switch stores the MAC address table of all the connected nodes, which helps it to send the data to the desired node.
ROUTER :-
- The router works on IP address.
- Routers normally connect LANs and WANs together.
- It has a dynamically updating routing table (stores IP Addressed) based on which they make decisions on routing the data packets.
GATEWAY :-
- Gateway is a device that connects dissimilar networks.
- Establishes an intelligent connection between a local network and external networks with completely different structures.
- Gateway is the ISP(Internet Service Provider) that connects the user to the internet. The gateway can also act as Firewall, API Gateways, etc.
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.
- The bridge acts on MAC/Physical Address.
- 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).
Wi-fi Card:-
It is similar like ethernet card that enables a Wi-Fi connectivity for the computers. The Wi-Fi Card is coming wit a small antenna. It is known as wireless NIC.
Network Topologies:
Topology: Topology refers to the way in which the device/computer/workstations attached to the network are interconnected. The layout of interconnection of devices in a
network is called Topology.
Different Topologies are: Star, Bus, Tree, Mesh.
BUS Topology: - The bus topology uses a common single cable (backbone cable) to connect all the workstations. Each computer performs its task of sending messages without the help of the central server. However, only one workstation can transmit a message at a particular time in the bus topology.
Advantages:
(i) Easy to connect and install.
(ii) Involves a low cost of installation time.
(iii) Can be easily extended.
Disadvantages:-
(i) The entire network shuts down if there is a failure in the central cable.
(ii) Only a single message can travel at a particular time.
(iii) Difficult to troubleshoot an error.
STAR Topology: -In Star topology, each node is directly connected to a central device like
Hub or Switch. It is most popular topology to form Local Area Networks (LAN).
Advantages:
(i) Easy to troubleshoot
(ii) A single node failure does not affects the entire network.
(iii) Fault detection and removal of faulty parts is easier.
(iv) In case a workstation fails, the network is not affected.
Disadvantages: -
(i) Difficult to expand.
(ii) Longer cable is required.
(iii) The cost of the hub and the longer cables makes it expensive over others.
(iv) All nodes are dependent on central node. if the central device (Switch) goes down
then entire network breaks down.
TREE Topology: - The tree topology combines the characteristics of the linear bus and
the star topologies. It consists of groups of star – configured workstations connected to a
bus backbone cable.
Advantages:
(i) Eliminates network congestion.
(ii) The network can be easily extended.
(iii) Faulty nodes can easily be isolated from the rest of the network.
Disadvantages:
➢ Uses large cable length.
➢ Requires a large amount of hardware components and hence is expensive.
➢ Installation and reconfiguration are very difficult.
Mesh Topology
In this networking topology, each communicating device is connected with every other device in the network. Such a network can handle large amounts of traffic since multiple nodes
can transmit data simultaneously. Also, such networks are more reliable in the sense that even if a node gets down, it does not cause any break in the transmission of data between other nodes.
Ring Topology
The nodes connected with each other thus forms a ring. The link in a ring topology is
unidirectional. Thus, data can be transmitted in one direction only (clockwise or counterclockwise).
Types of Computer Network:
A computer network may be small or big as per number of computers and other
network devices linked together. A computer network may contain devices ranging from
handheld devices (like mobile phones, tablets, laptops) connected through Wi-Fi or
Bluetooth within a single room to the millions of computers spread across the globe.
Based on the size, coverage area, data transfer speed and complexity, a computer network
may be classified as: (PLMW)
PAN (Personal Area Network): A Personal Area Network is computer network
organized around an individual person. It generally covers a range of less than 10 meters.
Personal Area Networks can be constructed with cables or wirelessly.
LAN (Local Area Network): A Local Area Network (LAN) is a network that is limited to
a small area. It is generally limited to a geographic area such as within lab, school or
building. It is generally privately-owned networks over a distance up to a few kilometers.
Now-a-days, we also have WLAN (Wireless LAN) which is based on wireless network.
MAN (Metropolitan Area Network): MAN is the networks cover a group of nearby
corporate offices or a city and might be either private or public. Cable TV network or cable
based broadband internet services are examples of MAN.
WAN (Wide Area Network):These are the networks spread over large distances, say
across countries or even continents through cabling or satellite uplinks are called WAN.
Typically, a WAN combines multiple LANs that are geographically separated. It is a
network of network. The world’s most popular WAN is the Internet.
Network Protocols:
HTTP (Hyper Text Transfer Protocol) :
➢ The Hyper Text Transfer Protocol is a set of rules which is used to access/retrieve
linked web pages across the web using web browser program.
➢ The more secure and advanced version is HTTP is HTTPS (HTTP Secure), which
controls the transfer of information in encrypted form to provide more security
and privacy.
➢ Other protocols like File Transfer Protocol (FTP) and Telnet can also be used with
URL. FTP is used to transfer files from web server to web client or vice-versa.
➢ Telnet is protocol which used for login on remote computer to access/transfer
files or trouble shooting.
FTP (File Transfer Protocol) is a network protocol for transmitting files between
computers over Transmission Control Protocol/Internet Protocol (TCP/IP) connections.
Point-to-Point Protocol (PPP) is a TCP/IP protocol that is used to connect one
computer system to another. Computers use PPP to communicate over the telephone
network or the Internet. A PPP connection exists when two systems physically connect
through a telephone line.
TCP/IP stands for Transmission Control Protocol/Internet Protocol and is a suite of
communication protocols used to interconnect network devices on the internet. TCP/IP
is also used as a communications protocol in a private computer network.
TELNET is commonly used by terminal emulation programs that allow you to log
into a remote host. However, TELNET can also be used for terminal-to-terminal
communication and interprocess communication. TELNET is also used by other protocols
(for example, FTP) for establishing a protocol control channel.
E-Mail (Electronic Mail):
Email is the short form of electronic mail. It is one of the ways of sending and
receiving message(s) using the Internet. An email can be sent anytime to any number of
recipients at anywhere. The message can be either text entered directly onto the email
application or an attached file (text, image, audio, video, etc.) stored on a secondary
storage. An existing file can be sent as an attachment with the email.
E-Mail Protocols:
Email are handled and exchanged through various mail servers in order to deliver
email to mail client. The mail client and mail servers exchange information with each
other using some protocols. The followings are commonly used protocols for email
handling-
SMTP (Simple Mail Transfer Protocol): This protocol is used to send emails from
sender to recipient’s mail server.
IMAP (Internet Message Access Protocol): This is a standard client/server protocol for
accessing e-mails from local e-mail server.
POP3 (Post Office Protocol 3): This protocol facilitates users to access mailboxes and
download messages to their computer.
Voice over Internet Protocol (VoIP):
➢ Voice over Internet Protocol or VoIP, allows voice call (telephone service) over the Internet. VoIP offers voice transmission over a computer network (IP) rather than through the regular telephone network. It is also known as Internet Telephony or Broadband Telephony. Examples of VoIP:- WhatsApp, Skype, Google Chat etc.
➢ VoIP works on the principle of converting the analogue voice signals into digital
and then transmitting them over the broadband line.
➢ These services are either free or very economical. That is why these days
international calls are being made using VoIP.
Introduction to web services:
World Wide Web (WWW):
World Wide Web, which is also known as a Web, is a collection of websites or web
pages stored in web servers and connected to local computers through the internet.
These websites contain text pages, digital images, audios, videos, etc. Users can access the content of these sites from any part of the world over the internet using their devices such as computers, laptops, cell phones, etc. The WWW, along with internet, enables the retrieval and display of text and media to your device.
There sources of the Web (HTML pages) are transferred via the Hypertext Transfer
Protocol (HTTP), may be accessed by users by a software application called a web
browser, and are published by a software application called a web server.
Tim Berners-Lee—a British computer scientist invented the revolutionary World Wide Web in 1990 by defining three fundamental technologies that lead to creation of www:
HTML ,URL, HTTP.
HTML(Hyper Text Markup Language):
Hyper Text Markup Language (HTML) is a language which is used to design
standardized Web Pages, so that the Web contents can be read and under stood from any computer using web browser.
Basic structure of every web page is designed using HTML. HTML uses tags to
define the way page content should be displayed by the web browser. Web pages are
stored as .html or .htm files.
Extensible Markup Language (XML): Extensible Markup Language is a markup
language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.
Domain Name: A domain name is a unique, easy-to-remember address used to access websites, such as 'google.com', and 'facebook.com'.
URL(Uniform Resource Locator):
URL—Uniform Resource Locator is a unique address of web resources located on the web. It provides the location and mechanism (protocol) to access the resource. URL is sometimes also called a web address.
A URL contains protocol, domain, sub domain and name of web page along with directory.
In the above URL, http is the protocol name, it can be https, http, FTP, Telnet, etc.
www is a sub domain. ncert.nic.in is the domain name. Textbook is directory and
textbook.htm is webpage.
The complete unique address of the page on a website is called URL (Uniform Resource Locator) e.g. http://www.cbse.nic.in/welcome.html
Since computers on the network are identified by its IP addresses, so it is required to convert a Domain name or URL typed in the Browser, in to its corresponding IP address. This process is called Domain Name Resolution. This resolution is done by the designated servers called DNS servers, provided by the Internet Service Providers (ISP) like BSNL, Airtel, Jio etc.
Website:
➢ Website is a collection of related web pages that may contain text, images, audio and video. The first page of a website is called home page. Each website has specific internet address (URL) that you need to enter in your browser to access a website.
➢ A website is a collection of web pages related through hyperlinks, and saved on a web server. A visitor can navigate pages by clicking on hyperlinks.
➢ The main purpose of website is to make the information available to people at
large. For example, a company may advertise or sell its products, a government
organization may publish circulars, float tenders, invite applications for
recruitments etc.
➢ A website can be accessed by providing the address of the website (URL) in the
browser. The main page of website (Home page) will be open when it is opened
on the browser.
Web Page:
➢ A web page is a document on the WWW that is viewed in a web browser. Basic
structure of a web page is created using HTML (Hyper Text Markup Language).
➢ To make web pages more attractive, various styling CSS (Cascading Style Sheets) and formatting are applied on a web page.
➢ Further, program codes called scripts also used to make webpage interactive and define different actions and behavior. JavaScript, PHP and Python are commonly used script language.
➢ The first page of the website is called a home page which contains Menus and
Hyperlinks for other web pages.
➢ A web page is usually a part of a website and may contain information in different forms, such as: text, images, audio & video, Hyperlinks, interactive contents (chat etc.)
A web page can be of two types: Static Web Page and Dynamic Web Page
Web Browsers:
➢ A web browser or simply ‘browser’ is a software application used to access
information on the World Wide Web. When a user requests some information, the
web browser fetches the data from a web server and then displays the webpage
on the user’s screen.
➢ The popular web browsers are Google Chrome, Mozilla Firefox, Internet Explorer,
Opera, Safari, Lynx and Netscape Navigator, Microsoft Edge etc.
➢ A web browser essentially displays the HTML documents which may include text, images, audio, video and hyperlinks that help to navigate from one web page to another. The modern browsers allow a wide range of visual effects, use encryption for advanced security and also have cookies that can store the browser settings
and data.
Web Server:
➢ A web server is used to store and deliver the contents of a website to web clients such as a browser.
➢ A Computer stores web server software and a website's contents (HTML pages,
images, CSS style sheets, and JavaScript files). The server needs to be connected to the Internet so that its contents can be made accessible to others.
➢ Web server as a software, is a specialized program that understands URLs or web addresses coming as requests from browsers, and responds to those requests.
➢ The server is assigned a unique domain name so that it can be accessed from
anywhere using Internet. The web browser from the client computer sends a HTTP
request for a page containing the desired data or service. The web server then accepts request, interprets, searches and responds (HTTP response) against request of the web browser. The requested web page is then displayed in the browser of the client. If the requested web page is not found, web server generates “Error: 404 Not found” as a response.
Web Hosting:
➢ A web hosting service is a type of Internet hosting service that allows individuals and organisations to make their website accessible via the World Wide Web. In Simple, uploading of website on Web Server is known as hoisting. To upload the website, we need some web space on server to upload website. This space is available on some nominal charges.
➢ All web servers are assigned a unique numeric address called IP address when
connected to the Internet. This IP address needs to be mapped/changed to domain name (Textual name) of the website using DNS (Domain Name Service). Thus, user can access website by providing domain name through a browser (URL). The domain name has to be registered (purchased) with an authorized agency i.e. Registrar Domain Names.
EXPANDED FORMS
ARPANET= Advance Research Project Agency Network (1969)
NIU= Network Interface Unit
LAN= Local Area Network
MAN= Metropolitan Area Network
WAN= Wide Area Network
ISP= Internet Service Provider
OSS= Open Source Software
ISDN= Integrated Service Digital Network
FLOSS= Free Libre Open Source Software
NIC= Network Interface Card
UTP= Unshielded Twisted Pair
STP= Shielded Twisted Pair
MODEM= Modulator Demodulator
RJ-45= Registered Jack -45
XML= Extensible Markup Language
FTP=File Transfer Protocol
TCP= Transmission Control Protocol
SMTP= Simple Mail Transfer Protocol
POP3= Post Office Protocol 3 (Version 3)
IMAP= Internet Message Access Protocol
IP= Internet Protocol
SLIP= Serial Line Internet Protocol
PPP= Point To Point Protocol
PDA= Personal Data Assistant
GSM= Global System For Mobile
SIM=Subscriber Identity Module
CDMA= Code Division Multiple Access
WLL= Wireless In Local Loop
WWW= World Wide Web
URL=Uniform Resource Locator
DHTML= Dynamic Hyper Text Markup Language
OSS= Open Source Software
GNU= GNU’s Not Unix
FSF= Free Software Foundation
OSI= Open Source Initiative
HTTP=Hyper Text Transfer Protocol
HTTPS : Hyper Text Transfer Protocol Secure
HTML= Hyper Text Markup Language
W3C= World Wide Web Consortium
ASP= Active Server Pages
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