Computer network connects two or more autonomous computers. The computers can be geographically located anywhere.

1. COMPUTER NETWORKS
By,
Dr. D. Veera Vanitha,
Associate Pofessor/ECE,
School of Engineering,
Avinashilingam Institute for Home Science and Higher Education for
Women, Coimbatore
Data Communications
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2. • Computer
network connects
two or more
autonomous
computers.
• The computers
can be
geographically
located anywhere.
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3. • Fundamental Characteristics
• Delivery
• Accuracy
• Timeliness
• Jitter
• Components of Communication System
• Message
• Sender
• Receiver
• Transmission Medium
• Protocol
• Data Representation
• Text
• Numbers
• Images
• Audio
• Video 3

4. • Data Flow (Communication between two devices)
• Simplex
• Half Duplex
• Full Duplex
• Network Criteria
• Performance
• Reliability
• Security
• Types of connection
• Point to Point
• Multipoint
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5. • Resource Sharing
• Hardware (computing resources, disks, printers)
• Software (application software)
• Information Sharing
• Easy accessibility from anywhere (files,
databases)
• Search Capability (WWW)
• Communication
• Email
• Message broadcast
• Remote computing
• Distributed processing (GRID Computing)
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6.  The network topology defines the way in which computers,
printers, and other devices are connected. A network topology
describes the layout of the wire and devices as well as the paths
used by data transmissions.
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7. • The mesh topology connects all
devices (nodes) to each other for
redundancy and fault tolerance.
• It is used in WANs to interconnect
LANs and for mission critical
networks like those used by banks
and financial institutions.
• Implementing the mesh topology
is expensive and difficult.
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8.  Commonly referred to as a linear bus, all the devices on a bus topology
are connected by one single cable
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9. • The star topology is the most
commonly used architecture in
Ethernet LANs.
• Larger networks use the
extended star topology also
called tree topology. When used
with network devices that filter
frames or packets, like bridges,
switches, and routers, this
topology significantly reduces
the traffic on the wires by
sending packets only to the
wires of the destination host.
Star topology
Tree topology
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10. • A frame travels around the ring,
stopping at each node. If a node
wants to transmit data, it adds the
data as well as the destination
address to the frame.
• The frame then continues around
the ring until it finds the destination
node, which takes the data out of the
frame.
• Single ring – All the devices on
the network share a single cable
• Dual ring – The dual ring
topology allows data to be sent
in both directions.
Unidirectional ring
Bidirectional ring
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11. • Network in small geographical Area (Room, Building or a Campus)
is called LAN (Local Area Network)
• Network in a City is call MAN (Metropolitan Area Network)
• Network spread geographically (Country or across Globe) is called
WAN (Wide Area Network)
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12. • Guided Media (Wired)
Twisted pair cable
Shielded
Unshielded
Coaxial Cable
Fiber Optic Cable
• Unguided Media (Wireless)
Radio Waves
Micro Waves
Infrared
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13. • E-mail
• Searchable Data (Web Sites)
• E-Commerce
• News Groups
• Internet Telephony (VoIP)
• Video Conferencing
• Chat Groups
• Instant Messengers
• Internet Radio
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14. • A protocol is a collection of rules and
procedures for two computers to exchange
information
• Protocol also defines the format of data that is
being exchanged
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15.  Open Systems Interconnection (OSI) is a set of internationally
recognized, non-proprietary standards for networking and for
operating system involved in networking functions.
7 Layers
7. Application Layer
6. Presentation Layer
5. Session Layer
4. Transport Layer
3. Network Layer
2. Data Link Layer
1. Physical Layer
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16.  The top layer of the OSI model
 Provides a set of interfaces for sending and receiving applications
and to use network services, such as: message handling and
database query processing
 Responsibility: The application layer is responsible for providing
services to the user.
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17.  Manages data-format information for networked communications
(the network’s translator)
 For outgoing messages, it converts data into a generic format for
network transmission; for incoming messages, it converts data
from the generic network format to a format that the receiving
application can understand
 This layer is also responsible for certain protocol conversions, data
encryption/decryption, or data compression/decompression
 A special software facility called a “redirector” operates at this
layer to determine if a request is network related on not and
forward network-related requests to an appropriate network
resource
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18.  Enables two networked resources to hold ongoing
communications (called a session) across a network
 Applications on either end of the session are able to
exchange data for the duration of the session
This layer is:
 Responsible for initiating, maintaining and terminating
sessions
 Responsible for security and access control to session
information (via session participant identification)
 Responsible for synchronization services, and for
checkpoint services
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19.  Manages the transmission of data across a network
 Manages the flow of data between parties by
segmenting long data streams into smaller data chunks
(based on allowed “packet” size for a given
transmission medium)
 Reassembles chunks into their original sequence at the
receiving end
 Provides acknowledgements of successful
transmissions and requests resends for packets which
arrive with errors
 The transport layer is responsible for the delivery
of a message from one process to another.
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20.  Handles addressing messages for delivery, as well as
translating logical network addresses and names into
their physical counterparts
 Responsible for deciding how to route transmissions
between computers
 This layer also handles the decisions needed to get data
from one point to the next point along a network path
 This layer also handles packet switching and network
congestion control
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21.  Handles special data frames (packets) between the Network
layer and the Physical layer
 At the receiving end, this layer packages raw data from the
physical layer into data frames for delivery to the Network
layer
 At the sending end this layer handles conversion of data into
raw formats that can be handled by the Physical Layer
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22.  Converts bits into electronic signals for outgoing
messages
 Converts electronic signals into bits for incoming
messages
 This layer manages the interface between the
computer and the network medium (coax, twisted
pair, etc.)
 This layer tells the driver software for the MAU
(media attachment unit, ex. network interface cards
(NICs, modems, etc.)) what needs to be sent across
the medium
 The bottom layer of the OSI model
 The physical layer is responsible for movements of
 individual bits from one hop (node) to the next.
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