KEY DATA COMMUNICATION TERMINOLOGY

• Link: connects adjacent nodes Wires, Cables, Any thing that physically connects two nodes
  

• Path: end-to-end route within a network

• Circuit: the conduit over which data travels

• Packetzing: dividing messages into fixed-length packets prior to transmission over a network’s communication media
  

• Routing: determining a message’s path from sending to receiving nodes

• The transmission medium may itself be a network, so route needs to be specified

Network
“A NETWORK is a set of devices (Nodes) connected by Communication Links”

• Node: Can be a Computer, Printer or any other device capable of sending or receiving
  

• The links connecting Nodes are called COMMUNICATION CHANNELS Networks- Why we need them?

Networks- Why we need them?
It is often impractical for devices to be directly connected for two major reasons:

• The devices are very far apart. They are expensive to connect just two devices with one in Lahore and other in Islamabad
  

• Large set of devices would need impractical number of connections e .g. Telephone Lines in the world and all the computers owned by a single organization

Solution to the Problem=Networks

• Solution is to connect all devices to a central system known as a NETWORK in which all terminals or computers share the links.
  

• Two Main Classifications of the Networks

• LANS
• WANS

DISTRIBUTED PROCESSING

• Instead of a single large machine being responsible for all aspects of a process ,each separate computer handles a subset of the task
  

• Example – Project Given as a part of the Course
• Example – Office Work

Advantages of Distributed Processing

• Security

A system designer can limit the kind of interaction that a given user can have with
the entire system.

• For example : Bank’s ATM

• Distributed Data bases

No one system need to provide storage capacity for the entire database

• For example WWW gives user access to pages stored anywhere on Internet

• Faster Problem Solving

Multiple computers working on a problem can solve a problem faster than a
computer working alone

• Security through Redundancy

Multiple computers running the same program provide security through redundancy
If one computer's hardware breaks down others cover up

• Collaborative Processing

Both multiple computers and multiple users can interact for a task

Digital Data Communication System

An Actual Digital Data Communication System Key Data Communication Terminology
Session: communication dialog between network users or applications
Different Types of this session for Info Exchange
Network: interconnected group of computers and communication devices
We will look into it in a little bit
Node: a network-attached device
Node can be any device in the network

Summary

• Data Communication
• Brief History of Communication
• Data Communication System
• Key Data Communication Terminology

Reading Sections

• Section 1.2, “Data Communications and Networking” 2nd Edition by Behrouz A.Forouzan
• Sections 1.1, 1.2, “Data and Computer Communication” 6th Edition by William Stallings

A little more complex Comm System

A little more complex Comm System

• User of a PC wishes to send a message ‘m’
• User activates electronic mail package e.g hotmail
• Enters the message via input device (keyboard)
• Character string is buffered in main memory as a sequence of bits ‘g’
• PC is connected to some trans system such as a Telephone Network via an I/O Transmitter like Modem
• Transmitter converts incoming stream ‘g’ into a signal ‘s’

RECEIVER SIDE

• The transmitted signal ‘s’ is subject to a number of impairments depending upon the medium
• Therefore, received signal ‘r’ may differ from ‘s’.
• Receiver attempts to estimate original ‘s’ based on its knowledge of the medium and received signal ‘r’
• Briefly buffered in the memory
• Data is presented to the user via an output device like printer, screen etc.
• The data viewed by user m’ will usually be an exact copy of the data sent ‘m’
• Receiver produces a bit stream g’(t)
• Briefly buffered in the memory
• Data is presented to the user via an output device like printer, screenetc.
• The data viewed by user m’ will usually be an exact copy of the data sent ‘m’

EXAMPLE-Telephone System

• Input to the Telephone is a message ‘m’ in the form of sound waves
• The sound waves are converted by telephone into electric signals of the same frequency
• These signals are transmitted w/o any modification over the telephone line
• Hence g(t) and s(t) are identical
• S(t) will suffer some distortion so that r(t) will not be the same as s(t)
• R(t) is converted back to sound waves with no attempt of correction or improvement of signal quality
• Thus m’ is not an exact replica of m

Components of a Data Comm. Systems

Components of a Data Com Systems
Components of a Data Com Systems
Any system is made up of more than one component. Similarly, a data communication
system is made up of 5 components as shown in the fig:

• Message
• Sender
• Receiver
• Medium
• Protocol

MESSAGE

• Information or Data to be communicated
• Can be text, numbers, video or any combination of these
• In short anything that can be represented using binary bits

Data Communication Messages
Files (meaningful collections of records)
Data/information requests (database queries, Web page requests,
etc.)
Responses to requests and commands or error messages
Status messages (about the network’s functional status)
Control messages transmitted between network devices to control
network traffic
Correspondence among network users

MESSAGE TYPES

SENDER

• Device that sends the data message
• Can be a Computer , Workstation, Video camera etc
• As already discussed, the data from the sender might not be in the appropriate format for the transmission medium and will need to be processed

RECEIVER

• Device that receives the message
• Can be a computer, workstation, Television etc
• At times, the data received from the transmission medium may not be in a proper form to be supplied to the receiver and it must be processed

MEDIUM

• Physical path that a message uses to travel from the Sender to the Receiver
• Can be a Copper Cable (Telephone), Coaxial Cable (Cable TV), Fiber Optic Cable, LASERS or Radio Waves (Wireless Medium)
• We will see that Data needs to be transferred in the form of ELECTROMAGNETIC signals and The Transmission Medium should be capable of carrying these EM Signals

Transmission Media

PROTOCOL

• Set of Rules Governing Communication
• Represents an Agreement between communication devices
• Without Protocol, two devices may be connected but they will not be able to communicate

EXAMPLE: Consider the communication between two
individuals. They can only communicate provided they
both speak the same language.

VAGUE DEFINITIONS We will clarify

Data Communication System
For Data Communication to occur, the communicating devices must be a part of a
communication system made up of some specific kind of hardware and software
This type of a system is known as a

“DATA COMMUNICATION SYSTEM”

Effectiveness of Data Comm. System
Effectiveness depends upon three fundamental characteristics:

• Delivery
• Accuracy
• Timeliness (Better NEVER than LATE)

Example of the POSTAL MAIL

TODAY’S EVERGHANGING & BUSY WORLD

• Today’s fast world demands better, secure and most of all FAST ways of communication
• Gone are the days when you had to wait a couple of weeks to get a letter from USA
• Why wait ONE week when you can get the information you require in just a split of a second, using what we know by the name of “DATA COMMUNICATION”.

HOW TO ACHIEVE THIS?

• How to achieve this ACCURACY, SECURITY and SPEED for the transfer of this information?
• What HARDWARE, and the SOFTWARE is needed ?
• And, what should be the MEANS of sending this info?

ARE SOME OF TOPIC WE WILL BE EXPLORING DURING THE COURSE OF
OUR STUDY

DATA COMMUNICATION

• When we communicate , we share information
• Information can be LOCAL or REMOTE
• Between Individuals LOCAL communication occurs face to face
• REMOTE communication occurs over a long distance
• When we refer to COMPUTER SYSTEMS, Data is represented in the form of Binary Units (Bits) in the form of Zeros (0’s) and One’s (1’s)
• Also the entities can most of the times be considered to be COMPUTERS

Data Communication Definition (Modified)

Therefore , our earlier definition can easily be modified to:
“Data Communication is the exchange of data (in the form of 0’s and 1’s)
between two devices (computers) via some form of the transmission medium.”

LOCAL and REMOTE Data Communication

LOCAL
Data communication is considered to be local if the communicating devices
are present in the same building or a similarly restricted geographical area
REMOTE
Data Communication is considered remote, if the devices are farther apart.

INTRODUCTION TO DATA COMMUNICATION

DEFINITION OF DATA COMMUNICATION
“Data Communication is the exchange of Information from one entity to the other
using a Transmission Medium”.

DEFINITION OF DATA COMMUNICATION (Cont’d)
As you can clearly notice, the definition of Data Communication although Simple
leaves many questions unanswered:

• Exchange??????
• Information?????
• Entities???????
• Transmission????
• Medium????

We will try to answer all these Questions in this Course

History of Data Communication
Data communications history represents a blend of histories, including:

• The history of the telecommunications industry
• The history of data communications, and
• The history of the Internet
• Telegraph 1837 Samuel Morse

Telegraph 1837 Samuel Morse
Modern telecommunication industry began in 1837 with the invention of
the telegraph by Samuel Morse
This led to building a telecommunications infrastructure of poles and
wires as well as to the development of communication hardware and
protocols

Telephone 1876 Alexander Graham Bell
Invention of telephone by Alexander Graham Bell in 1876 and the
development of wireless communication technology by Guglielmo
Marconi in the 1890s set the stage for today’s communication industry

By 1950’s
By 1950s, telephone and telegraph companies had developed a network of
communication facilities throughout the industrialized world

1970’S
Although development of databases, languages, operating systems, and
hardware was strong from 1950s to 1970s, large-scale data communication
systems did not emerge until the 1970s.

This was stimulated by 3 major developments:

• Large-scale integration of circuits reduced cost and size of terminals and communication equipment
• New software systems that facilitated the development of data communication networks
• Competition among providers of transmission facilities reduced the cost of data circuits