2. A brief history of origin of Internet.
Sharing Resources
◦ The Internet started in the 1960s as a way for government researchers to share information. Computers in the '60s were
large and immobile and in order to make use of information stored in any one computer, one had to either travel to the site of
the computer or have magnetic computer tapes sent through the conventional postal system.
◦ Another catalyst in the formation of the Internet was the heating up of the Cold War. The Soviet Union's launch of the
Sputnik satellite spurred the U.S. Defense Department to consider ways information could still be disseminated even after a
nuclear attack. This eventually led to the formation of the ARPANET (Advanced Research Projects Agency Network), the
network that ultimately evolved into what we now know as the Internet. ARPANET was a great success but membership was
limited to certain academic and research organizations who had contracts with the Defense Department. In response to this,
other networks were created to provide information sharing.
◦ January 1, 1983 is considered the official birthday of the Internet. Prior to this, the various computer networks did not have a
standard way to communicate with each other. A new communications protocol was established called Transfer Control
Protocol/Internetwork Protocol (TCP/IP). This allowed different kinds of computers on different networks to "talk" to each
other. ARPANET and the Defense Data Network officially changed to the TCP/IP standard on January 1, 1983, hence the
birth of the Internet. All networks could now be connected by a universal language.
3. Introduction to Computer Network
◦ A computer network is a group of devices connected with each other through a transmission medium such as
wires, cables etc. These devices can be computers, printers, scanners, Fax machines etc.
◦ The purpose of having computer network is to send and receive data stored in other devices over the network.
These devices are often referred as nodes.
◦ These are basic components of a computer network
◦ Message: It is the data or information which needs to be transferred from one device to another device over a computer
network.
◦ Sender: Sender is the device that has the data and needs to send the data to other device connected to the network.
◦ Receiver: A receiver is the device which is expecting the data from other device on the network.
◦ Transmission media: In order to transfer data from one device to another device we need a transmission media such as wires,
cables, radio waves etc.
◦ Protocol: A protocol is a set of rules that are agreed by both sender and receiver, without a protocol two devices can be
connected to each other but they cannot communicate. In order to establish a reliable communication or data sharing between
two different devices we need set of rules that are called protocol. For example, http and https are the two protocols used by
web browsers to get and post the data to internet, similarly smtp protocol is used by email services connected to the internet.
4. Features of a Computer Network
◦ Performance: Performance of a computer network is measured in terms of response time. The response time of sending and
receiving data from one node (computer in a computer network are often referred as node) to another should be minimal.
◦ Data Sharing: One of the reason why we use a computer network is to share the data between different systems connected with
each other through a transmission media.
◦ Backup: A computer network must have a central server that keeps the backup of all the data that is to be shared over a network
so that in case of a failure it should be able to recover the data faster.
◦ Software and hardware compatibility: A computer network must not limit all the computers in a computer network to use same
software and hardware, instead it should allow the better compatibility between the different software and hardware configuration.
◦ Reliability: There should not be any failure in the network or if it occurs the recovery from a failure should be fast.
◦ Security: A computer network should be secure so that the data transmitting over a network should be safe from unauthorized
access. Also, the sent data should be received as it is at the receiving node, which means there should not be any loss of data
during transmission.
◦ Scalability: A computer network should be scalable which means it should always allow to add new computers (or nodes) to the
already existing computer network. For example, a company runs 100 computers over a computer network for their 100 employees,
lets say they hire another 100 employees and want to add new 100 computers to the already existing LAN then in that case the
local area computer network should allow this.
5. Computer Network Architecture
◦ A Computer Architecture is a design in which all computers in a computer network are organized. A architecture
defines how the computers should get connected to get the maximum advantages of a computer network such as
better response time, security, scalability etc. The two most popular computer architectures are P2P (Peer to
Peer) and Client-Server architecture.
◦ Peer to Peer Architecture
◦ In peer to peer architecture all the computers in a computer network are connected with every computer in the network. Every
computer in the network use the same resources as other computers. There is no central computer that acts as a server rather
all computers acts as a server for the data that is stored in them.
◦ Advantages of a Peer to Peer Architecture
◦ 1. Less costly as there is no central server that has to take the backup.
2. In case of a computer failure all other computers in the network are not affected and they will continue to work as same as
before the failure.
3. Installation of peer to peer architecture is quite easy as each computer manages itself.
◦ Disadvantages of a Peer to Peer Architecture
◦ 1. Each computer has to take the backup rather than a central computer and the security measures are to be taken by all
the computers separately.
2. Scalability is a issue in a peer to Peer Architecture as connecting each computer to every computer is a headache on a
very large network.
6. Computer Network Architecture
◦ Client Server Architecture
◦ In Client Server architecture a central computer acts as a hub and serves all the requests from client computers. All the
shared data is stored in the server computer which is shared with the client computer when a request is made by the client
computer.
◦ Advantages of Client Server Architecture
1. Data backup is easy and cost effective as there is no need to manage the backup on each computer.
2. Performance is better as the response time is greatly improves because the server is more powerful computer than the other computers
in the network.
3. Security is better as unauthorized access are denied by server computer and all the data goes through the server.
4. Scalability is not an issue in this Architecture as large number of computers can be connected with server.
◦ Disadvantages of Client Server Architecture
1. In case of server failure entire network is down.
2. Server maintenance cost is high as the server is the main component in this Architecture
3. Cost is high as the server needs more resources to handle that many client requests and to be able to hold large amount of data.
7. Transmission Modes in Computer
Networks
◦ Transmission mode means transferring data between two devices. It is also known as a communication mode.
Buses and networks are designed to allow communication to occur between individual devices that are
interconnected. There are three types of transmission mode:-
1. Simplex Mode –
In Simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can
transmit, the other can only receive. The simplex mode can use the entire capacity of the channel to send data in one
direction.
Example: Keyboard and traditional monitors. The keyboard can only introduce input, the monitor can only give the output.
2. Half-Duplex Mode –
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the
other can only receive, and vice versa. The half-duplex mode is used in cases where there is no need for communication in
both directions at the same time. The entire capacity of the channel can be utilized for each direction.
Example: Walkie-talkie in which message is sent one at a time and messages are sent in both directions.
3. Full-Duplex Mode
In full-duplex mode, both stations can transmit and receive simultaneously. In full-duplex mode, signals going
in one direction share the capacity of the link with signals going in another direction, this sharing can occur in
two ways:
◦ Either the link must contain two physically separate transmission paths, one for sending and the other for
receiving.
◦ Or the capacity is divided between signals travelling in both directions.
8. What is modulation?
◦ Modulation is the process of converting data into radio waves by adding information to an
electronic or optical carrier signal. A carrier signal is one with a steady waveform -- constant
height, or amplitude, and frequency
◦ How modulation works
◦ Modulation is usually applied to electromagnetic signals: radio waves, lasers/optics and
computer networks. Modulation can even be applied to a direct current -- which can be
treated as a degenerate carrier wave with a fixed amplitude and frequency of 0 Hz -- mainly
by turning it on and off, as in Morse code telegraphy or a digital current loop interface. The
special case of no carrier -- a response message indicating an attached device is no longer
connected to a remote system -- is called baseband modulation.
◦ Modulation can also be applied to a low-frequency alternating current -- 50-60 Hz -- as with
powerline networking.
9. What are the types of modulation?
There are many common modulation methods, including the following, which is an incomplete list:
• Amplitude modulation (AM): The height (i.e., the strength or intensity) of the signal carrier is
varied to represent the data being added to the signal.
• Frequency modulation (FM): The frequency of the carrier waveform is varied to reflect the
frequency of the data.
• Phase modulation (PM): The phase of the carrier waveform is varied to reflect changes in the
frequency of the data. In PM, the frequency is unchanged while the phase is changed relative to
the base carrier frequency. It is similar to FM.
• Polarization modulation: The angle of rotation of an optical carrier signal is varied to reflect
transmitted data.
• Pulse-code modulation: An analog signal is sampled to derive a data stream that is used to
modulate a digital carrier signal.
• Quadrature amplitude modulation (QAM): Uses two AM carriers to encode two or more bits in
a single transmission.
10. Why use modulation
The carrier wave used by radio frequency (RF) transmissions doesn't carry much
information itself. To include speech or data, another wave has to be superimposed
on the carrier wave, thus changing the shape of the carrier wave. The process of
doing so is called modulation. To transmit sound, the audio signal must first be
converted into an electric signal, using a transducer. After conversion, it is used to
modulate a carrier signal.
Analog vs. digital
Modulation schemes can be analog or digital. An analog scheme has an
input wave that varies continuously like a sine wave. In digital modulation
scheme, voice is sampled at some rate and then compressed and turned
into a bit stream, and this in turn is created into a particular kind of wave
which is then superimposed on the carrier signal.
11. Internet and its use in business, emails
◦ Widespread access to the internet is now a common feature of the workplace
and it is important that both employers and employees have an understanding
of the benefits and the problems that such access can bring. Any organisation
should aim to gain the maximum value from the internet and email, while
remaining aware of the technical and commercial risks that can arise if the
technology is misused.
◦ The main business uses of the internet and email are:
• searching for information and data
• sending and receiving information, notes, memos, documents and messages
• as a marketing tool, to promote an organisation or to facilitate e-commerce
• as a recruitment tool
• for web-based training.
12. Appropriate and Inappropriate Use of the
Internet
◦ Time spent online may not always be time well spent: it is not
immediately apparent whether someone browsing the web is working or
not. An employee may undertake focused and efficient searching for
work-related information or may covertly browse for acceptable non-
work-related information (eg sports results) or unacceptable non-work-
related material
◦ In the absence of an internet policy it is still possible to control web
browsing. If an employee is spending a disproportionate amount of time
on the internet, they may be disciplined for misusing working time and/or
failing to meet the requirements of the job in the same way as any other
breach of their terms of employment.
13. Downloading Information
◦ Managers need to be aware of the particular issues relating to permanent downloads where
data is obtained from the internet and stored locally. Such downloads may involve large
amounts of data and can therefore:
• be extremely time-consuming and costly
• be detrimental to the network bandwidth
• contain inaccurate and inappropriate information
• be a security risk
• be in breach of copyright (or even patent).
◦ Obtaining accurate information
◦ The internet gives instant access to vast amounts of information, much of it less reliable than it
may appear. Managers must be aware of this risk and warn their staff accordingly. Unless it
comes from a regulated and official source such as a government site, information obtained
online should preferably be cross-checked and details of its source should be kept in case
future checking is required.
14. Obtaining inappropriate text and images
◦Although it is possible for measures to be taken to
prohibit access to certain sites, the internet is so vast
that it is impossible to guarantee that all such access
can be automatically prevented. Therefore, an
organisation has to state unequivocally in an internet
policy that downloading offensive, obscene or
indecent material is forbidden, and managers have to
take the necessary steps to ensure that this policy is
upheld.
15. Use of social media
◦Although it is possible for measures to be taken to
prohibit access to certain sites, the internet is so vast
that it is impossible to guarantee that all such access
can be automatically prevented. Therefore, an
organisation has to state unequivocally in an internet
policy that downloading offensive, obscene or
indecent material is forbidden, and managers have to
take the necessary steps to ensure that this policy is
upheld.
16. Access to Email
◦ Managers have a responsibility to implement an organisation’s policy on using
email. A fundamental aspect of this is whether employees will be allowed to use
workplace email for personal messages. If personal use of email is allowed, the
policy may still place limits on this use, eg personal messages must only be read or
sent outside working hours (for example during lunch breaks) or where the matter
is genuinely urgent. If no specific rules exist then it is the responsibility of the line
manager to ensure that employees are not taking undue advantage of the
situation. Employees should be made aware of the rules and the sanctions for
breaching them via the internet policy. Additionally, the organisation’s disciplinary
procedure should state that excessive or inappropriate use of email for personal
purposes will be regarded as misconduct. Employees should also be made aware
of the possibility of the interception of email.
17.
18. Title Lorem Ipsum
LOREM IPSUM DOLOR SIT AMET,
CONSECTETUER ADIPISCING ELIT.
NUNC VIVERRA IMPERDIET ENIM.
FUSCE EST. VIVAMUS A TELLUS.
PELLENTESQUE HABITANT MORBI
TRISTIQUE SENECTUS ET NETUS.
