Data Communication & Computer Networks

dingdongboomNetworking and Communications

Oct 27, 2013 (3 years and 11 months ago)

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1

Data Communication & Computer
Networks

Lecture 13

2

Data Communication




The transfer of data/messages from
one point to another point.

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Basic Elements of Communication
System


Three basic elements of communication
system are:
-

1.
A
sender

(source) which creates the message
to transmitted.

2.
A
medium

which carries the message.

3.
A
receiver

(destination) which receives the
message.

4

Basic Elements of Communication
System

Sender


(source)

Receiver

(destination)

Medium

5

Data Transmission Modes


There are three ways, modes for
transmitting data from one point to
another. These are
simplex
,
half
-
duplex

and
full
-
duplex
.

6

Data Transmission Modes


Simplex:


If transmission is simplex, communication can take place in only
one direction. For example, radio & T.V. etc.


Half
-
Duplex:


A half
-
duplex system can transmit data in both directions, but
only in one direction at a time. For example, wireless etc.


Full
-
Duplex:


A full
-
duplex system is used that allows information to flow
simultaneously in both directions on the transmission path. For
example, telephone etc.


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Data Transmission Modes

Sender

Sender or

Receiver

Sender &

Receiver

Sender &

Receiver

Receiver or

Sender

Receiver

Simplex

Half
-
Duplex

or

Full
-
Duplex

and

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Digital & Analog Transmission


Digital transmission

sends data as distinct
pulses, either on or off, in much the same
way that data travels through the
computer.


Analog transmission
, a continuous
electrical signal in the form of a wave.

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Digital & Analog Transmission


10

Digital & Analog Transmission


Frequency:

It is the rate (cycles/sec or HZ) at which the
signals repeat.


Bandwidth:

It is the range of frequencies that is available
for the transmission of data.


Channel:

A channel is a portion of the communications
medium allocated to the sender and receiver for
conveying information between them.


Modems:

A modem is a device that converts a digital
signal to an analog signal and vice versa.

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12

Transmission Media


There are several types of physical
channels (communication media) through
which data can be transmitted from one
point to another. Some of the most
common data transmission medium are
as under:
-

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Wire Pairs:

It is also known as
twisted pair
.
Wire pairs are wires twisted together to form a cable,
which is thin insulated. Wire pairs are inexpensive.


Application:

Telephone networks, within buildings &
LAN etc.


Benefits & Drawbacks:


Cheap


Low data rate


Short range


Easy to work with


Transmission Media

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Transmission Media


Coaxial Cable:

are groups of specially
wrapped and insulated wire lines that are
able to transmit data at very high rates.
These cables can transmit data much
faster than wire pairs.


Application:

Long distance telephone
transmission, Local Area Networks etc.

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Transmission Media


Fiber Optics:

Instead of using electricity to
send data, fiber optics uses light.


Application:

Long haul trunks, Metropolitan trunks, LAN
& WAN etc.


Benefits & Drawbacks:


Greater capacity


Smaller size & weight


Lower attenuation

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Protocol


A protocol is a set of rules and procedures
established to control transmission
between two points.


Some common protocols are:
-


TCP/IP (Transmission Control Protocol/Internet
protocol)


IPX (Internet Packet Exchange) etc.

17

Computer Networks


Network:

A computer system that uses communications
equipment to connect two or more computers and their resources.


Network Interface Card (NIC):

A circuit board that can be inserted
into a slot inside a personal computer to allow it to send and receive
messages on a LAN.


Node:

A device, usually a personal computer, that is connected to a
computer.


Topology:

The physical layout of a network is called a topology.


Some common network topologies are as under:
-

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Network Topologies


Star Topology:


A star network has a
hub computer that is
responsible for
managing the network.


All messages are routed
through the central
computer, which acts as
a traffic cop to prevent
collision.

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Network Topologies


Star Topology:


Any connection failure
between a node and the
hub will not affect the
overall system.


However, if the hub
computer fails, the
network fails.

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Network Topologies


Ring Topology:


A ring network links all
nodes together in a circular
chain.


Data messages travel in
only one direction around
the ring.


Any data passes by, is
examined by the node to
see if it is addressee; if
not, the

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Network Topologies


Ring Topology:


Data is passed on to
the next node in the
ring.. Since data travels
in only one direction,
there is no danger of
data collision.


However, if one node
fails, the entire network
fails.


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Network Topologies


Bus Topology:


A bus network has a single line to
which all the network nodes are
attached.


Computers on the network
transmit data in the hope that it
will not collide with data
transmitted by other Nodes.


If this happens, the sending node
simply tries again.


Furthermore, if one node fails, it
does not affect the rest of the
network.

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Computer Networks


There are two ways to organize the
resources in networking, which are
:
-


Peer to Peer Networking


Client/Server Networking


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Computer Networks


Peer to Peer Networking:

In which, a group of
computers communicate directly with each other,
rather than through a central server.


Client/Server Networking:

A client/server
arrangement involves a server, the computer that
controls the networks.

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Kinds of Networks


There are different kinds of
networks, for example,


LAN (Local Area Networks)


WAN (Wide Area Networks)


MAN (Metropolitan Area Network)

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Kinds of Networks


Local Area Networks:

A network which
spreads over limited geographical area is
called as LAN.


Wide Area Networks:

A WAN is a network
of geographically distant computers. (e.g.
Internet)

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Local Area Networks


LAN refers to a network with the following
characteristics:
-


The network is confined to a small area,
typically a single building.


The network consists of a shared transmission
medium.


The data rate on the network is high,
anywhere from 1 Mbps to 100 Mbps.

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Local Area Networks


LAN Protocols:

The two most common network
protocols for LANs are
Ethernet

&
Token Ring

network.


Ethernet


The network protocol which uses the high speed
network cable.


Ethernet uses a bus topology, inexpensive and relatively simple to
set up.


Since all the computers in a LAN use the same cable to transmit
and receive data, they must follow a set of rules about when to
communicate; otherwise two or more computers could transmit at
the same time,

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Local Area Networks


Ethernet


Causing lost messages. So, if the
cable is in use, the computer must wait.


When the cable is free from other
transmissions, the computer can begin
transmitting immediately.


This transmission method is called by the
fancy name of
carrier sense multiple access
with collision detection
(CSMA/CD).

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Local Area Networks


Token Ring


which is closely associated with IBM, works on the
concept of a ring network topology, using a token, a kind of
electronic signal.


Only one token is available on the network. When a computer
on a network wishes to transmit, it first captures the token;
only then can it transmit data.


When the computer has sent its message, it releases the
token back to the network.


Since only one token is circulating around the network, only
one device is able to access the network at a time.

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Network Applications


Electronic Mail


Voice Mail


Facsimile Technology (FAX)


Electronic Data Interchange (EDI)


E

Commerce


Instant Banking


Video Conferencing etc.

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Internet


& its use…


ISP
-

An internet service provider provides the facility to
connect the internet.


Browser


is a software on the user’s computer that allows the
user to access the internet, for example, Internet explorer &
Netscape communicator etc.


Domain Name


Which is the address of the specific web page.


Search Engine


is a software that lets a user specify search
terms; the search engine then finds sites that fit those terms.