ITEC102 (SIr Jonel) Flashcards
The transfer of data or information from one location to another
Data Communication
ELEMENTS OF DATA COMMUNICATION SYSTEM
Transmitter or sender or source
Receiver or sink or destination
Medium
Message
The computer or device that is used for sending the data from one location to other
Transmitter
The computer or device that receives the data
It is also known as ‘sink’
Receiver
The path or link through which data transferred from sender to receiver
Medium
The data or information which is sent from sender to receiver
It is the main element of data communication system, due to which data communication occur.
Message
There are two main categories of data communication media:
Guided Media
Unguided Media
are the physical links through which signals are transferred. These are also called bounded media. These include various types of cables. The type of cable chosen for a network depends upon the network’s topology,size and speed.
Commonly used guided media include coaxial cables, wire pairs and fiber-optic cables.
GUIDED MEDIA
are the logical links through which signals are transferred. These are the natural parts of environment that can be used to transfer signals in the form of waves. The atmosphere and space are examples of unguided media.
Commonly used methods of transmission through unguided media are microwave and satellite transmission.
UNGUIDED MEDIA
The manner in which data is transmitted from one location to another
data transmission mode
three different modes for transmitting data from one location to another.
Simplex Mode
Half Duplex Mode
Full Duplex Mode
data is transmitted in only on direction. A terminal can only send data and cannot receive data or it can only receive data but cannot send it. In this mode, the flow of information is uni-directional. It is not possible to confirm successful transmission of data. So it is rarely used for data communication.
This mode is normally used for Remote control devices in which one device can only send data and other can only receive data
SIMPLEX MODE
data can be transmitted in both directions, but only in one direction at a time. Therefore data can be sent and received alternatively. Its disadvantage is that a lot of time is wasted in changing direction of flow of data. So, the transmission rate for this mode is slow.
Use: It is possible to confirm the transmission of data in this mode. So this is normally used in wireless communication system.
HALF-DUPLEX MODE
data can be transmitted in both directions at the same time. In this mode, no time is wasted in changing direction of flow of data like Half-duplex mode. Therefore it is the fastest and most efficient mode.
Use:
Telephone communication
FULL-DUPLEX MODE
The transfer of any kind of information from
one location to another.
DATA TRANSMISSION
means sending a stream of
bits or bytes from one location to another via
transmission medium such as copper wire,
fiber optics, laser, radio,infra red light,
Bluetooth.
Communication
most basic information unit used in
computing & information theory
Bit
a series of 8 bits, also called a
character.
Byte
reads & writes information in bits
Computer
electric or electromagnetic
representation of data.
Can be coded for security purposes.
Signals
converts a message into a signal,
which is carried to a receiver by the communication channel.
Transmitter
2 types of signals;
Analog Signal
Digital Signal
are continuous electrical signals that vary with
time & represented by a waveform.
All natural signal around us is of this type.
ANALOG SIGNAL
measure of wavelength at any given point of time. (Measured in Volt [V])
Amplitude
number of times waveform repeats itself in second. (Measured in Hertz[Hz]
Frequency
distance between two corresponding points on a waveform. (Measured in Meter [m])
Wavelength
progress of a wave over time in relationship to a fixed point or other wave with same frequency amplitude.
Phase
non-continuous & they change in individual steps.
Consists of pulse & digits with discrete levels or values.
Value of pulse constant, but there is an abrupt change from one digit to another.
Have 2 amplitude levels which represents two voltage pulses.(1/0, true/false, high/low etc)
Positive voltage pulse = 1, no pulse =0
Computer is a digital device & they work on digital
signals.
DIGITAL SIGNAL
signal which is transmitted at input &
signal received at output does not always match due to transmission flaws over the transmission channel.
TRANSMISSION FLAWS
Cause of transmission flaws:
Noise
Attenuation
Latency
unwanted signal which can disturb or harm
Noise
device that regenerates digital
signal.
Repeater
device with amplify or regenerate
analog signal.
Amplifier
a loss of power.
Attenuation
Also known as delay, is an expression of how
much time it takes for a packet of data to get
from one designated point to another.
LATENCY
is the addition of information/signal to an
electronic or optical signal carrier.
MODULATION
A device that performs modulation
modulator.
A device that performs the inverse operation
which is demodulation
demodulator.
A device that can do both modulation &
demodulation
modem.
Modulation methods:
Amplitude modulation (AM)-the amplitude of
voltage applied to the carrier is varied over time.
Frequency modulation (FM)- the frequency of the career waveform in varied in small but meaningful amounts.
Phase modulation (PM)-the natural flow of the
alternating current waveform is delayed temporarily.
transmitting multiple signals over a single
communication line or computer channel
MULTIPLEXING
2 common multiplexing techniques:
Frequency Division Multiplexing (FDM) - separates
signals by modulating the data onto different
carrier frequencies.
Time Division Multiplexing (TDM) -separates
signals by interleaving bits one after the other.
TYPES OF DATA TRANSMISSION
Serial transmission
Parallel transmission
2 types of transmission modes:
Asynchronous transmission
Synchronous transmission
A technique widely used in personal computers to provide connectivity to printers, modems, fax machines etc.
Codes are sent in untimely manner with unevenintervals between characters.
Sending & receiving data is controlled by start & stop
bit.
Asynchronous transmission
Technique of transmission in which the transmitter & receiver are synchronized.
Codes are sent from transmitting station to
receiving station to establish the synchronization. Data is transmitted in continuous stream.
Synchronous transmission
XML stands for
EXtensible Markup Language
was designed to describe data.
XML
are not predefined unlike HTML XML DTD and XML Schema define rules to describe data
XML tags
set of rules that allow us to specify our own set of elements and attributes.
DTD (Document type Definition)
is valid if it has an attached DTD and document is structured according to rules defined in DTD.
XML Document
provide additional information about Elements.
Attributes
Serves same purpose as database schema
Set of pre-defined simple types
XML Schema
is a language that defines path
expressions to locate document data
XPath
Basic Steps to develop JDBC Application
Import JDBC classes (java.sql.*).
Load JDBC drivers
Connect and Interact with database
Disconnect from database
provides basic services to manage set of JDBC drivers
DriverManager
JDBC provides following three classes for sending SQL statements to server:
Statement
PreparedStatement
CallableStatement
can be executed using any of the objects.
SQL Query
