Data Communication Communication is for sharing information
Sharing can be local or remote Local communication between
individuals is face to face Remote communication takes place over
distance Telecommunication means communication at a distance
includes telephony,telegraphyetc
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Data-refers to information presented in whatever form agreed
upon by the parties creating and using the data. Data communication
Exchange of data b/w two devices through some form of transmission
medium such as wire cable.
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SIMPLIFIED NETWORK MODEL Networks: Computer network A
collection of computing devices that are connected in various ways
in order to communicate and share resources Usually, the
connections between computers in a network are made using physical
wires or cables However, some connections are wireless, using radio
waves or infrared signals
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The generic term node or host refers to any device on a network
Node can be a computer,printer,or any other device capable of
sending or receiving data generated by other node on the network
Data transfer rate The speed with which data is moved from one
place on a network to another
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Distributed Processing Most n/w use distributed processing.
Ie.a task is divided among multiple computers Instead of one single
large m/c responsible for all aspects of a process,separate
computer handles a subset
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Network Cryteria A n/w must meet a no of cryterias 1.
Performance 2. Reliability 3. Security
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Performance Measured in different ways like 1.Transit Time 2.
Response time Transit Time: Amount of time required for a message
to travel from one device to another Response Time Elapsed time
between an enquiry and a response
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Performance depends on no of factors including no of users,type
of transmission medium,capabilities of connected h/w,efficiency of
s/w etc. Performance is evaluated by using measures like
1.Throughput 2.Delay We need more throughput and less delay when we
send more data to n/w we can increase the throughput but increase
in delay due to congestion in n/w
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Reliability Measured by frquency of failure,the time take a
link to recover from a failure Security Security issues include
protecting data from unauthorized access,damage,implementing
policies and procedures for recovery from data losses
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Simplified Network Model
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PHYSICAL STRUCTURES Types of Connection n/w is 2 or more
devices connected through links Link is a connecting pathway that
transfers data from one device to other Imagine link as a line
drawn b/w 2 points For communication to occur the two devices must
be connected to same link at the same time
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2 possible type of connection Point to point Provides dedicated
link between 2 devices Entire capacity is reserved for transmission
between those two devices Multi Point Also called multi drop
connection More than specific device share a single link Capacity
of channel is shared
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Point to Point and Multipoint
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PHYSICAL TOPOLOGY Refers to way in which a n/w is laid out
physically 2 or more devices connect to a link 2 or more links form
a topology ie. Topology means it is a representation of
relationship of all the links and linking devices(nodes) to one
another
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CATEGORIES OF TOPOLOGY MESH STAR BUS RING
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CATEGORIES OF TOPOLOGY
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MESH TOPOLOGY Every device has dedicated point to point link to
every other device The link carry traffic only b/w the two devices
it connects In a mesh n/w no of links with n nodes is n(n-1) If
physical link is in duplex mode we need n(n-1)/2 duplex mode
links
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MESH TOPOLOGY WITH 5 DEVICES
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MESH TOPOLOGY Advantages Use of dedicated link guarantees that
each connection can carry its own data load and thus eliminates
traffic problems that can occur when links must be shared by
multiple devices Roubst: if one link become unusable it does not in
capacitate entire system Privacy/Security:every message travels
only through dedicated line.only intended recipient can see it
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MESH TOPOLOGY Advantages Point to point link makes fault
identification and fault isolation easy Traffic can be routed to
avoid links with suspected problems This facility enables n/w
manager to discover the precise location of the fault & aids in
finding the cause and solution
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MESH TOPOLOGY Disadvantages Amount of cabling and I/O ports are
very high because each device must be connected to each device and
also installation and reconnection are difficult Bulk wiring is
greater than available space h/w for connecting I/O ports is
expensive
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STAR TOPOLOGY Each device has a dedicated point to point link
to a central controller usually called a hub Devices are not
directly linked to one another Does not allow direct traffic b/w
devices If one device wants to send data to other it sends data to
controller and then send data to other device
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STAR TOPOLOGY
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Advantages Each device needs only one link and one I/O port to
connect to it to any no of others.So it is easy to install and
reconfigure Less cabling is needed. Addition and deletion involve
only one connection. Between device and hub Robstness If one link
fails other links are active,only one is affected Help easy fault
identification and fault isolation
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STAR TOPOLOGY Disadvantages Depending to one single point known
as hub If hub is down whole system is down
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BUS TOPOLOGY A multipoint connection One long cable act as a
backbone to link all devices in a n/w
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BUS TOPOLOGY Nodes are connected to bus cable by drop lines and
taps Dropline: connection running b/w device and main cable Tap:
Connector that splices into the main cable
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BUS TOPOLOGY Advantages Ease of installation Less cabling than
mesh ie. Backbone cable can be laid along the most efficient
path,then connected to nodes by droplines of various lengths
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BUS TOPOLOGY Disadvantages Difficult reconnection and fault
isolation A bus is usually designed to be optimally efficient at
installation so it is difficult to add devices Signal reflection at
the tap can cause degradation in quality This degradation can be
controlled by limiting no and spacing of devices connected to
backbone so, Adding new devices include changing backbone Fault or
break in bus cable stops all transmission
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RING TOPOLOGY Each device has a dedicated point to point
connection with only the two devices on either side of it A signal
is passed along the ring in one direction from device to device
until it reaches destination Each device in the ring incorporates a
repeater When a device receives a signal intended for another
device its repeater regenerates the bits and passes them
along.
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RING TOPOLOGY
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Advantages Easy to install and configure Each device is
connected to only its immediate neighbour To add or delete a device
requires changing only 2 connections Fault isolation is easy
Generally a signal is circulating all times.if one device does not
receive a signal within a specified period it can issue an alarm
The alarm alerts the n/w operator and its isolation
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RING TOPOLOGY Disadvantages A break in a ring (eg:disabled
station) can disable the entire n/w