basics of computers

1. Applications of Networking
1. Resource Access
Regardless of the physical location of the resources and the users, networks can provide
special computing resources with convenient access at any time to its users. These resources sharing
may be of specialized computers, software or other devices that are expensive or unique. For example
accessing a corporate supercomputer from workstations at remote research laboratories.
2. Data Access
Networks can provide access to unique database to its local and remote users.
3. Communication and Data Exchange
Networks allow users to exchange data, graphs or documents and to communicate using
email, bulletin boards or by teleconference, irrespective of the time or their location.
4. Decentralization of Data Processing
A complicated job can be divided into multiple modules and can be distributed to different
departments for processing.
5. Easy Communication
Various organizations cooperating in a task can communicate with each other on network
and exchange information.
Internet Security
As internet is open to all, the security, privacy, authenticity and anonymity issues play a
vital role as one need to be sure about these things, then only he can use the Internet to its fullest
extent. As information and its transfer are crucial for every one who is using the internet, there need to
be provisions, which is reliable then only one can connect to internet. The security of internet can be
divided into two broad categories, namely:

2. 1. Client-Server Security
2. Data & Transaction Security
Client-Server Security
This security is for preventing unauthorized access to restricted databases and other
information which is confidential. This is an authorization mechanism, which makes it sure that the users,
who are authorized only should be able to connect and access the information. These mechanisms are required
to ensure that only authenticated users can access the resources, which they are entitled to. Password
protection, encrypted smart cards, biometrics, firewalls etc. are some of the methods adopted to ensure client-
server security.
Data & Transaction Security
As the data transmissions and transactions occur across the network, there are fair chances that
they can be intercepted, read and manipulated as well as the source and destination can be tracked. To prevent
this one has to provide security to the data and transactions, which is usually done by using data encryptions,
which is implemented through various cryptographic methods.
Security Methods for Client/Server & Data/Transaction Security
1. Password Scheme:
This is an easy solution to provide security, so that unauthorized users do not get access to the
data. This is the first level of security, which can be provided. Here, the authorized users are assigned
user names and a password is associated to them, which are to provided when connecting to the site.
But this security measure can be broken easily, if common words or proper names are used as
passwords, but if alphanumeric passwords of bigger length are used, then it is very difficult to break
them.
Another problem is that, if the login is remote, then the password travels through the system to
server for authentication, in meantime, it can be trapped, for this reason the passwords are to be
encrypted before transmitting them.
But in spite of these threats, password schemes are still the most popular forms of ensuring
security.

3. 2. Firewalls
Firewall is accepted as the network protection mechanism, it is a barrier between corporate
network and the outside world, which will ensure that the authentic users only connect as well only the
data which is harmless enters and leaves the system.
The term firewall can be defined as a device, a computer or a router which is placed between
the network and the internet to control and monitor the traffic between the inside and outside world.
Firewall is a device which is used to shield vulnerable areas from various dangers. The firewall
system is located at a gateway point which actually is the connecting point to the outside world.
Firewalls come in many varieties and offer different features, but the basic feature is to filter the traffic
of data and control it.
3. Encryption
This method of data and transaction security is used for retaining confidentiality and integrity
of the data being transmitted. Data confidentiality is that property, which makes data contents to be
safe from being read, while on the path of transmission, which is made sure by using cryptography
algorithms for encrypting data, which no one can interpret. Along with data being confidential, it has
to remain unmodified, while on transit i.e. the data should be intact without any modifications, while it
is on way to destination. This is made sure by using various encryption techniques like Secret-Key
Cryptography, Data Encryption Standard(DES), Public Key Cryptography RSA etc.
Analog Signals
Analog signals are continuous in nature, they carry information in the form of waves e.g., the way
sound travels in the medium such as telephone lines. Analog communication uses general purpose
communication channels. These signals are characterized by two parameters such as amplitude and
frequency.
Digital Signals
Digital signals are discrete in nature. They transfer information in the form of 0s and 1s. in digital
communication, data are transmitted directly in binary form that is a sequence of 0s and 1s. to transmit
binary data over these channels 0s and 1s should be converted to the electrical signals. This is done by
Modem (modulator-demodulator). Digital signals are preferred over analog signals. Because of the

4. discrete nature, these signals are not affected by noise or any other disturbances. Moreover, computer
at the receiving end does not perform any conversion as in analog signals i.e. analog to digital.
Packet Transmission:
• Computers use data grouped into packets for transmission
• Local Area Networks
• Wide Area Networks
• Addressing and Routing
Concepts of Packets:
• Computer networks divide data into small blocks called packets
• Packets are send individually
• Often called packet networks and packet switching networks
• Motivation for using packets
o Sender and receiver needs to coordinate transmission to ensure that data
arrives correctly
o Helps determine which blocks arrive intact and which do not
o Computers often share underlying connections and hardware
o Packet switching helps ensure fairness to access
Shared Resources:
1. The first networks
1.1. A 5 MB file at 56 Kbps will take 12 min to transfer from A to D
1.2. B & C must wait
2. Packet networks
2.1. Divide data into packets of 1000 bytes each
2.2. A sends a packet to D taking only 143 ms
2.3. B transmits data to C
2.4. A continues
3. No long delays

5. Packets and TDM
1) Time Division Multiplexing
a) Many resources take turns accessing the shared communication resources
2) All sources receive prompt service
3) The source with less
Packets and Frames
1. Packet refers to a small block of data
2. Each hardware technology uses different packet format
3. Frame denotes packet used with specific type of network
4. EX : RS-232 mechanism
4.1. Does not include a mechanism that allows a sender to signal the end of a block of
characters
4.2. Sending and receiving computers must agree on such details
5. Network systems can choose two unused values to define format
6. EX: RS-232 can use frame delimiters
6.1. Soh –start of header
6.2. Eot – end of transmission
7. Overhead is an disadvantage
7.1. An extra, unnecessary character between blocks of data
8. Advantageous when large delays or computer crashes
8.1. Missing eot indicates sending computer crashed
8.2. Missing soh indicates receiver missed beginning of frame

6. Packet transmission:
A packet transmission rate control scheme between nodes on a wireless Ad-hoc
network is proposed considering the characteristics of Wireless LAN rent transmission
efficiencies by different transmission distances. Many energy efficient routing algorithms
researches have been conducted only on the assumption of ideal experimental cases. This
paper considers the way of finding suitable transmission rate for the transmission distances
between nodes on a mobile Ad-hoc networks so that a more realizable method is presented.
In this research, a controlling algorithm for transmission data rates by the distances
between mobile nodes is realized using Fuzzy logic, possibly available to be applied to Ad-
hoc network routing, and simulations are conducted to verify the enhancements in
throughput.
Long distance communication:
method of forming a long distance communication channel between two
telephone devices each of which are connected to a PSTN, said method
comprising
a user of one of said telephone devices initiating and establishing a
telephone communication with a first commercial access provider node of
INTERNET and providing thereto a telephone address,
using INTERNET to establish a communication channel between said first
commercial access provider node and a second commercial access provider
node of INTERNET and providing said telephone address to said second
commercial access provider node,
said second commercial access provider node using said telephone address
and a telephone dial out capability of said second commercial access
provider node to establish a communication with a telephone device at the
telephone address using a PSTN, and
using the INTERNET communication channel to link said telephone devices and
form a real time voice communication between said telephone devices.
2. A method as claimed in claim 1 including, after initiating said
telephone communication with said first commercial access provider node,
said first commercial access provider node communicates with said user to
establish authorization for completing a long distance communication.
3. A method as claimed in claim 1 wherein said first and second commercial
access provider nodes encrypt signals there between and decrypt received
signals such that signals transmitted over INTERNET are encrypted.

7. 4. A method as claimed in claim 1 wherein said telephone devices are
conventional telephones.
5. A method as claimed in claim 4 wherein signals transmitted between said
commercial access nodes using INTERNET are encrypted.
6. A method as claimed in claim 1 wherein the originating telephone device
has a predetermined arrangement with said first commercial access provider
node and said second telephone device has no prior relationship with
either of said commercial access provider nodes.
7. A method as claimed in claim 5 wherein each commercial access node has
different DID telephone addresses for voice and facsimile transmissions.
8. A method of establishing a long distance telephone communication between
an initiating telephone device and a receiving device telephone identified
by a telephone address, said method comprising using a PSTN to initiate a
telephone communication with a commercial access provider node of a
digitized packet based network and provide the node with said telephone
address, said commercial access provider node causing a real time voice
communication channel to be formed between said telephone devices, which
communication channel includes an initial PSTN segment between the
initiating telephone device and said commercial access provider node a
digitized packet based network segment between said commercial access
provider node, and a further commercial access provider node and a PSTN
segment between said further commercial access provider node and the
telephone device identified by the telephone address, wherein the further
commercial access provider node uses the telephone address and the PSTN to
initiate the PSTN segment there between.
9. A method as claimed in claim 8 wherein said telephone devices are
conventional telephones.
10. A method of forming a long distance telephone communication between a
first telephone device and a second telephone device which communication
is capable of transmitting real time voice communications similar to
existing long distance voice telephone communications, comprising the
steps of
forming an initial telephone link between the first telephone device and a
commercial access provider node of a digitized packet based network and
providing thereto a telephone address of the second telephone device, said
commercial access provider forming an appropriate digitized packet based
communication channel with a further commercial access provider node
located in closer proximity to the location of the second telephone device

8. and providing thereto said telephone address, said further commercial
access provider establishing a telephone link with said second telephone
device using said telephone address, and then linking said telephone
devices using said digitized packet based communication channel thereby
forming a real time voice communication between said telephone devices.
11. A method as claimed in claim 10 wherein said second telephone device
requires no prearrangement with said further commercial access provider
node.
12. A communication arrangement for long distance telephone to telephone
voice communication comprising a first provider node of a digitized packet
based network having means to allow users to initiate a telephone
communication with a desired telephone device identified by a telephone
address by the steps of initially forming a communication with said first
provider node and providing said telephone address thereto,
said first provider node cooperating with a second provider node of said
digitized packet network to form a real time voice communication channel
there between and said second provider node including dial out capabilities
which are used upon receipt of the telephone address provided thereto to
form a telephone communication with the telephone device,
said second provider cooperating with said first provider node to link the
telephone devices using a digitized packet based network segment between
said provider nodes and using PSTN segments between the initiating
telephone device and the first provider node and between the second
commercial access provider node and said telephone device identified by
said telephone address,
wherein the first and second provider nodes appropriately process the
signals for transmission using the digitized packet based network.
13. A communication arrangement as claimed in claim 12 wherein the signals
transmitted over the digitized packet based network are encrypted by said
commercial access provider nodes.
14. A long distance telephone communication arrangement having three
distinct communication segments, comprising a first communication segment
which carries voice communication over a PSTN between a first telephone
device and a first commercial access provider node of a digitized racket
based network a second segment between said first commercial access
provider node and a second commercial access provider node of said
digitized packet based network which exchange digitized voice packets
there between based on communications received from the first and third
segments, said third segment carrying voice communication over a PSTN

9. between a second telephone device and said second commercial access
provider node after said second commercial access provider node has
established said third segment with said second telephone device, and
wherein said second commercial access provider establishes said third
segment with said second telephone device by using the telephone address
of said second telephone device provided thereto by said first provider
which received the telephone address in a communication from said first
telephone device.
15. A long distance telephone communication arrangement as claimed in claim
14 wherein said first and second commercial access provider nodes carry
out all necessary signal conversion to and from the first and third
segments.
16. A long distance telephone communication arrangement as claimed in claim
14 wherein said first and second commercial access provider nodes encrypt
signals transmitted on the second segment.
17. A long distance telephone communication arrangement as claimed in claim
14 wherein said first and second commercial access provider nodes convert
the signals for transmission by the second segment to a different form
relative to the signals carried by the first and third segments.
18. A long distance telephone communication arrangement having three
distinct communication segments for transmitting a signal, comprising a
first communication segment which carries voice communication over a PSTN
between a first telephone device and a first commercial access provider of
a digitized packet based network, a second segment between said first
commercial access provider and a second commercial access provider of said
digitized packet based network which exchange digitized voice packets
there between based on communications received thereby, and a third segment
which carries voice communication over a PSTN between a second telephone
device and said second commercial access provider and wherein said first
and second commercial access providers convert the signal to and from the
first and third segments whereby the signal carried by the second segment
is in a form different from the signal carried by at least one of the
first and third segments, and wherein said second commercial access
provider establishes said third segment with said second telephone device
by using the telephone address of said second telephone device provided
thereto by said first provider which received the telephone address in a
communication from said first telephone device.
19. A long distance telephone communication arrangement comprising a
digitized packet based network segment between at least two commercial
access providers of the digitized packet based network, said commercial
access providers cooperating to form a communication channel having a real

10. time digitized packet based communication segment, said communication
channel linking a first telephone device and a second telephone device,
said communication channel being established upon receipt of an initial
telephone communication with one of said commercial access providers from
said first telephone device which communication includes a telephone
address of the second telephone device, and where after said telephone
address is transmitted over the digitized packet based network to the
other commercial access provider which uses the same to form a telephone
communication with said second telephone device identified by the
telephone address, and thereafter said telephone devices are connected
using the digitized packet based segment.