Data Communication
Agenda
Data Communication
• Data Communication
• Communication Protocol
• Forms of data Transmission
• Data Transmission Mode
• Types of data Transmission
• Transmission Media
• Uses of Communication Technologies
Data Communication
• Data communication is a process of
transferring data electronically from one
place to another.
• Basic elements of data communication are
– Sender
– Receiver
– medium
Elements of data Communication (cont’d)
• Sender
– Sender is a device that sends message. The message
may be consist of text, numbers, pictures etc. It is also
called source or transmitter.
• Medium
– Medium is the path that connects sender and receiver.
It is used to transmit data. The medium can be a
copper wire, a fiber optic cable, microwave etc
• Receiver
– Receiver is a device that receives message. It is also
called Sink. The receiver can be computer, printer, or
another computer related device. The receiver must
be capable of accepting the message.
Elements of data Communication (cont’d)
Message
Medium
Sender
Receiver
Communication Protocol
• Protocol:
– The procedure of data transformation in the form
of software is commonly called protocol.
– This protocol is a set of rules for exchanging
information among computer.
– These protocols define:
• How the communication channel is established
• How information is transmitted
• How errors are detected and corrected
Functions of Communication Protocols
• The main functions of communication
software protocols are as follows
– Data Sequencing
– Data Routing
– Data Flow
– Error Control
Forms of Data Transmission
• There are two forms of data transmission
–Digital Data Transmission
–Analog data Transmission
Digital Data Transmission
• Forms of Data Transmission Digital Data
Transmission Digital signal is a sequence of
voltage represented in binary forms, these signals
are in the form of electrical pulses of ON and OFF.
• Digital signals are faster and efficient, they
provide low error rates, high transmission speed
and high- quality voice transmission.
• All data communication between the computers
is in digital form.
• In digital signals high voltage is represented by 1
and low voltage is represented by 0.
Analog data Transmission
• Analog Data Transmission Analog signal is a
continuous electrical signal in the form of
wave, which is known as Carrier wave.
• Telephone line is the most commonly used
media for analog transmission of data. Light,
sound, radio and microwave are also examples
of analog signals.
Data Transmission Modes
• 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.
• Simplex mode
• Half Duplex mode
• Full Duplex mode
Simplex mode
• Data is transmitted from the sender to receiver
only, (eg: from a central computer to a dumb
terminal).
• The communication can only take place in one
direction and it is not possible for the receiver to
send data back.
• An example of simplex transmission would be
data being sent to an electronic notice board
such as those found in train stations and airports.
Half Duplex mode
• Data can travel in both directions but not at the
same time. Each end of the communications link
acts as sender and receiver, (eg: two-way
communication between computers and other
computers that may be connected to a hub).
• Controls will exist to ensure that the devices do
not send at the same time.
• One human example of this type of
communication is the use of walkie-talkies, where
each person communicating must indicate when
they have finished speaking.
Full duplex mode
• Data can travel in both directions
simultaneously, (e.g: two or more computers
connected to a network device such as a
switch that provides full duplex activity).
• A telephone is full-duplex device.
• Full duplex mode is a faster way of data
transmission as compared to half duplex.
Types of Data Transmission
• Asynchronous Transmission
• Synchronous Transmission
Asynchronous Transmission
• In asynchronous the transmission of data is generally
without the use of an external clock signal, where data
can be transmitted intermittently rather than in a
steady stream.
• Any timing required to recover data from the
communication symbols is encoded within the
symbols.
• The most significant aspect of asynchronous
communications is that data is not transmitted at
regular intervals, thus making possible variable bit rate.
• And that the transmitter and receiver clock generators
do not have to be exactly synchronized all the time.
Application
• Asynchronous activities take place outside of
real time system.
• As asynchronous does not require a constant
bit rate.
• For examples file transfer, email and the World
Wide Web.
Drawback
• Overhead of start and stop bits.
• Asynchronous transmission is relatively slow due
to the increased number of bits and gaps.
Synchronous Transmission
• In Synchronous the transmission of data is sent in
a continuous stream at a constant rate.
• Synchronous communication requires that the
clocks in the transmitting and receiving devices
are synchronized running at the same rate.
• so the receiver can sample the signal at the same
time intervals used by the transmitter. No start or
stop bits are required.
• For this reason synchronous communication
permits more information to be passed over a
circuit per unit time.
• Over time the transmitting and receiving
clocks will tend to drift apart, requiring
resynchronization.
• Synchronous communication is direct
communication that occurs in real time.
• That take place face-to-face, and as
technology has evolved, can take place
irrespective of distance
• (ex. telephone conversations and instant
messaging)
Application
• Most common use is in the ASCII terminals.
• High speeds communication links established
using synchronous modems.
Drawback
• The clock frequency should be same at both the
sending and receiving ends.
• No tolerance in clock frequency is allowed.
Transmission Media
• Guided Media
• Unguided Media
• Guided Media (Wired)
Guided media, which are those that provide a
conduit from one device to another, includes
– Twisted pair Cable
– Coaxial Cable
– Fiber Optics
Guided Media
• Twisted Pair Cable
– The wires in Twisted Pair cabling are
twisted together in pairs.
– Each pair would consist of a wire used
for the +ve data signal and a wire used
for the -ve data signal.
– Any noise that appears on 1 wire of the
pair would occur on the other wire.
– Twisted Pair cables are most effectively
used in systems that use a balanced
line method of transmission.
• Two types of Twisted Pair Cable
– STP (Shielded Twisted Pair)
– UTP (Un shielded Twisted Pair)
Guided Media
• Coaxial Cable
– Coaxial Cable consists of 2 conductors. The
inner conductor is held inside an insulator
with the other conductor woven around it
providing a shield.
– An insulating protective coating called a
jacket covers the outer conductor. The outer
shield protects the inner conductor from
outside electrical signals.
– The distance between the outer conductor
(shield) and inner conductor plus the type of
material used for insulating the inner
conductor determine the cable properties or
impedance.
– The excellent control of the impedance
characteristics of the cable allow higher data
rates to be transferred than Twisted Pair
cable.
Guided Media
• Fiber Optics
– Optical Fiber consists of thin
glass fibers that can carry
information at frequencies in
the visible light spectrum and
beyond.
– The typical optical fiber
consists of a very narrow
strand of glass called the Core.
– Around the Core is a concentric
layer of glass called the
Cladding
Unguided Media
• Unguided media transport electromagnetic
waves without using a physical conductor.
• This type of communication is often referred
to as wireless communication
• Types are
– Radio Wave
– Microwave
– Infrared
Unguided Media
• Radio Waves:
– Radio waves are used for
multicast communications, such
as radio and television, and
paging systems.
– They can penetrate through
walls.
– Highly regulated.
– Use Omni directional
antennas
Unguided
Media
• Microwaves
– Microwaves are used for
unicast communication
such
as
cellular
telephones,
satellite
networks, and wireless
LANs.
– Higher frequency ranges
cannot penetrate walls.
– Use directional antennas
point to point line of sight
communications.
Unguided
media
• Infrared
– Infrared signals can be used for short range communication in a
closed area using line-of-sight propagation.
– Low frequency
– Wireless mouse, keyboards etc
Uses of Communication Technologies
• The uses of communication technologies are
as follows
• Voice Mail
• Fax
• E-Mail
• Instant Messaging
• Newsgroups
• Internet Telephony
• Video Conferencing
• Collaboration
• Groupware
• Chat Rooms
• Global Positioning System