Download Networking Fundadmentals • What is Computer Network? A

Networking Fundadmentals
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What is Computer Network?
A computer network is a interconnection of geographically distributed multiple
computers in such a way that meaningful transmission and exchange of information
become possible among them.
In easy terms, a computer network is a number of computers (usually called terminals)
interconnected by one or more transmission paths. The transmission path often is the
telephone line, due to its convenience and universal presence. The goal is to transfer and
exchange of data between the computers. Sharing of information, sharing of resources
(Hardware and Software) and sharing of processing load are some of major objectives of
computer network.
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Need for Networking
Computer network provide several important advantages to enterprises and individuals.
These are:
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Exchange of Information – These days organization are widely dispersed, with offices
located in diverse path of the country and the world. If the computer network exists
between the computer (located in various offices) the exchange of information is
possible.
Even for a smaller organization information exchange among various departments
such as store department, sales counter is easily handled using computer networks.
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Sharing of Resources – The networking of computers permits the sharing of
resources. For example, a user sitting at site A may be using a laser printer available
only at site B and user at site B may access a file that resides at site A.
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Load Sharing – Sharing of processing is load is another major advantage of computer
network. For instance, if a computer becomes saturated with too much work at one
site, the work can be reloaded through the network to another computer in the
network. This movement of jobs is called load sharing.
Even a particular computation can be partitioned into a number of sub computations
that can run concurrently. Then a computer network allows to distribute the
computation among various sites to run the computation concurrently to speed up the
whole operation.
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Reliability – Networking also supports the critical function of backup. In the event, a
computer fails, its counter-part can assume its functions and workload. This capability
is especially important in system such as those used for air traffic control. In the
event, a computer malfunction, backup computer rapidly take over and assume
control of operation without endangering air travelers.
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Flexible working environment – The use of networking allows a very flexible
working environment. Employee can work at home by using terminals tied through
networking into the computer at office. Many employees now carry terminals or
portable personal computers on tours and connect to the network.
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Data Communication Terminologies
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Components of Computer Network
A network is a group of computers connected together for the purpose of sharing data
with one another. Although networks have been used in business environments for many
years, they are becoming increasingly common in homes as a means of sharing an
Internet connection. The various parts of a computer network are as follows
Client – A client is a computer system which uses a network to access a remote
service from the server. It can access all the applications or information from the main
server. A client is also called as a node.
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Host (Computer, Laptop) – The first and foremost requirement in establishing a
network is the computer or laptop on the side of both sender and receiver.
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Network Interface Card (NIC) – A network card, network adapter, is a piece of
computer hardware designed to allow computers to communicate over a computer
network. It provides physical access to a networking medium and often provides a
low-level addressing system. Each network interface card has its unique ID. This is
written on chip, which is mounted on the card.
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Ethernet Cable – Ethernet cables connect network devices such as modems, routers,
and adapters. They transmit data during the Ethernet protocol. A network interface
card is installed in each computer and is assigned a unique address.
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Internet Connection – To connect to the Internet, a network needs an Internet
connection like dial up, broadband, ISDN, Cable or Leased line.
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Modem – Modem stands for Modulator/Demodulator. We know that a computer only
understands the language of ‘0’ and ‘1’ i.e. binary language.
Suppose you want to view a website http://www.google.co.in . The modem from the
sender’s side modulates the digital data into a signal which is compatible with the
telephone line i.e. analog signals. The receiving modem at your workplace
demodulates this analog signal back into digital data. Hence, a modem modulates as
well as demodulates the signal. Speed of modem is measured in bps(bits per second).
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Intranet – Intranet refers to a computer network within an organization. Intranet uses the
internet protocol technology to share any part of information securely. Intranet is
generally restricted to the employees of an organization. For example, the employees of
the same bank are interlinked with each other through the intranet. The private
information cannot be accessed by any outside person.
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Extranet – Extranet refers to a computer network that allows controlled access from the
outside for specific business or educational purposes. For example, the customers of a
private bank can access the bank’s website and make financial transactions. It does not
grant access to an organization’s entire network. It is only part of a company’s intranet
that can be accessed by users outside the company.
Types of Computer Network
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Local Area Network – An interconnection of computers and peripherals devices
contained within a limited geographical area utilizing a communication. A local area
network is a network that is confined to a relatively small area. It is generally limited to a
geographic area such as a lab, school or building.
In a LAN, one computer is designated as the file server. It stores all of the software that
controls the network, as well as the software that can be shared by the computer attached
to the network. Computers connected to the file server are called workstations. A LAN
consists of the following components-
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Two or more computers.
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Software to control the operation of computers.
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Peripheral devices like printer, scanners etc.
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Cables to connect the computers.
Metropolitan Area Network – MAN is a network that shares some of the characteristics
of both LAN and WAN. The MANs usually cover wider geographic area (upto 50km in
diameter) than LANs and frequently operate at speed a bit lesser than LAN but quite
higher as compared to WAN. The main objective of MANs is to interconnect LANs
located in entire city or metropolitan area. MAN is designed to extent over entire city. It
may be single network such as a cable television network or it may be means of
connecting a number of LANs into a larger network so that resources can be shared.
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Wide Area Network – Wide area network comes into picture when we have two or more
computers located at different places, linked by communication facilities like
telecommunication or satellite signals. The most common examples of WAN type
network in our daily life if Telecom system. The usage of WAN is limited to very large
organization and government agencies. The main characteristic of WAN is that it requires
a public telecommunication media to transfer data.
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Personal Area Network – A computer network which is used for communication among
computers and different information technological devices close to each other is called a
PAN. Some examples of the devices that are used in a PAN are personal computers,
printers, fax machines, telephones etc. A PAN may include wired and wireless devices.
Network Layouts(Toplogy)
The term Network Topology defines the geographic arrangement of computernetworking
devices. The term Topology refers to the way in which the various nodes or computers of a
network are linked together. It describes the actual layout of the computer network hardware.
Two or more devices connect to a link; two or more links form a topology. Topology
determines the data paths that may be used between any pair of devices of the network.
The selection of a Network Topology for a network can not be done in isolation as it affects
the choice of media and the access method used. Because it determines the strategy used in
wiring a building for a network and deserves some careful study.
Bus Topology
The physical Bus Network Topology is the simplest and most widely used of the network
designs. It consists of one continuous length of cable (trunk) that is shared by all the nodes
in the network and a terminating resistor (terminator) at each end that absorbs the signal
when it reaches the end of line. Without a terminator the electrical signal would reach the end
of copper wire and bounce back, causing errors on the network.
Data communication message travels along the bus in both directions until it is picked up by
a workstation or server NIC. If the message is missed or not recognized, it reaches the end of
the cabling and dissipates at the terminator. Bus Network Topology requires a multipoint
connection.
All nodes on the bus topology have equal access to the trunk. This is accomplished using
short drop cables or direct T-connectors. The number of devices and the length of the trunk
can be easily expanded.
Features of Bus Topology
1. It transmits data only in one direction.
2. Every device is connected to a single cable
Advantages of Bus Topology
1. It is cost effective.
2. Cable required is least compared to other network topology.
3. Used in small networks.
4. It is easy to understand.
5. Easy to expand joining two cables together.
Disadvantages of Bus Topology
1. Cables fails then whole network fails.
2. If network traffic is heavy or nodes are more the performance of the network
decreases.
3. Cable has a limited length.
4. It is slower than the ring topology.
Ring Topology
The physical ring Topology is a circular loop of point-to-point links. Each device connects
directly to the ring or indirectly through and interface device or drop cable. Message
travel around the ring from node to node in a very organized manner. Each workstation
checks the message for a matching destination address. If the address doesn't match the node
simply regenerates the message and sends it on its way. If the address matches, the node
accepts the message and sends a reply to the originating sender.
Features of Ring Topology
1. A number of repeaters are used and the transmission is unidirectional.
2. Date is transferred in a sequential manner that is bit by bit.
Advantages of Ring Topology
1. Transmitting network is not affected by high traffic or by adding more nodes, as only
the nodes having tokens can transmit data.
2. Cheap to install and expand
Disadvantages of Ring Topology
1. Troubleshooting is difficult in ring topology.
2. Adding or deleting the computers disturbs the network activity.
3. Failure of one computer disturbs the whole network.
Star Topology
The physical star Topology uses a central controlling hub with dedicated legs pointing in
all directions – like points of a star. Each network device has a dedicated point-to-point link
to the central hub. There is no direct link between these computers and the computers can
communicate via central controller only. This strategy prevents troublesome collisions and
keeps the lines of communications open and free of traffic.
The routing function is performed by the central controller which centrally controls
communication between any two computers by establishing a logical path between them. It
means that if one computer A wants to send data to another computer B, Computer A sends
the data to the controller & this controller then sends the data to computer B.
Advantages of Star Topology
Features of Star Topology
1. Every node has its own dedicated connection to the hub.
2. Acts as a repeater for data flow.
3. Can be used with twisted pair, Optical Fibre or coaxial cable.
Advantages of Star Topology
1. Fast performance with few nodes and low network traffic.
2. Hub can be upgraded easily.
3. Easy to troubleshoot.
4. Easy to setup and modify.
5. Only that node is affected which has failed rest of the nodes can work smoothly.
Disadvantages of Star Topology
1. Cost of installation is high.
2. Expensive to use.
3. If the hub is affected then the whole network is stopped because all the nodes depend
on the hub.
4. Performance is based on the hub that is it depends on its capacity
MESH Topology
It is a point-to-point connection to other nodes or devices. Traffic is carried only between two
devices or nodes to which it is connected. Mesh has n (n-2)/2 physical channels to link hn
devices
Features of Mesh Topology
1. Fully connected.
2. Robust.
3. Not flexible.
Advantages of Mesh Topology
1. Each connection can carry its own data load.
2. It is robust.
3. Fault is diagnosed easily.
4. Provides security and privacy.
Disadvantages of Mesh Topology
1. Installation and configuration is difficult.
2. Cabling cost is more.
3. Bulk wiring is required.
TREE Topology
It has a root node and all other nodes are connected to it forming a hierarchy. It is also called
hierarchical topology. It should at least have three levels to the hierarchy.
Features of Tree Topology
1. Ideal if workstations are located in groups.
2. Used in Wide Area Network.
Advantages of Tree Topology
1. Extension of bus and star topologies.
2. Expansion of nodes is possible and easy.
3. Easily managed and maintained.
4. Error detection is easily done.
Disadvantages of Tree Topology
1. Heavily cabled.
2. Costly.
3. If more nodes are added maintenance is difficult.
4. Central hub fails, network fails.
Transmission Modes in Computer Networks
Transmission mode means transferring of data between two devices. It is also called
communication mode. These modes direct the direction of flow of information. There are
three types of transmission mode. They are :
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Simplex Mode
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Half duplex Mode
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Full duplex Mode
SIMPLEX Mode
In this type of transmission mode data can be sent only through one direction i.e.
communication is unidirectional. We cannot send a message back to the sender.
Unidirectional communication is done in Simplex Systems.
Examples of simplex Mode is loudspeaker, television broadcasting, television and remote,
keyboard and monitor etc.
HALF DUPLEX Mode
In half duplex system we can send data in both directions but it is done one at a time that is
when the sender is sending the data then at that time we can’t send the sender our message.
The data is sent in one direction.
Example of half duplex is a walkie- talkie in which message is sent one at a time and
messages are sent in both the directions.
FULL DUPLEX Mode
In full duplex system we can send data in both directions as it is bidirectional. Data can be
sent in both directions simultaneously. We can send as well as we receive the data.
Example of Full Duplex is a Telephone Network in which there is communication between
two persons by a telephone line, through which both can talk and listen at the same time.
In full duplex system there can be two lines one for sending the data and the other for
receiving data.
What is switching
Switching: Every time in computer network you access the internet or another computer
network outside your immediate location, your messages are sent through a maze of
transmission media and connection devices. The mechanism for moving information between
different computer network and network segment is called switching in computer network.
For example: - whenever a telephone called is placed, there are numerous junctions in the
communication path that perform this movement of data from one network onto another
network.
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