DATA COMMUNICATION Lecture-1

DATA COMMUNICATION
Lecture-1

Overview of Lecture 1
Data Communication
Brief History of Communication
Data Communication System
Key Data Communication Terminology
DATA COMMUNICATION DEFINITION
“Data Communication is the exchange of Information from one entity to the other using a Transmission Medium”
   
History of Data Communication
Telegraph 1837 Samuel Morse
Telephone 1876 Alexander Graham Bell
By 1950’s
1970’S
Today
DATA COMMUNICATION
“Data Communication is the exchange of Information from one entity to the other using a Transmission Medium”
   
Data Communication Definition (Modified)

“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 Communication
LOCAL
Communicating devices are present in the same building or a similarly restricted geographical area

LOCAL and REMOTE Communication
REMOTE
Communicating devices are present farther apart

VAGUE DEFINITIONS
We will clarify
Data Communication System
For Data Communication to occur, communicating devices must be a part of a system made up of some specific kind of hardware and software. This system is known as

 “DATA COMMUNICATION SYSTEM”


Effectiveness of Data Comm. System
Effectiveness depends upon three fundamental characteristics:
  Delivery
  Accuracy
  Timeliness
Components of a Simple Data Communication System
Components of a Data Communication System
A Data communication system is made up of 5 components:
Message
Sender
Receiver
Medium
Protocol
Message Types
Transmission Media
A Complex Data Comm. System
EXAMPLE – Electronic Mail
An Actual Digital Data Communication System
Key Data Communication Terminology
Session: communication dialog between network users or applications

Network: interconnected group of computers and communication devices

Node: a network-attached device

Key Data Communication Terminology
Link: connects adjacent nodes

Path: end-to-end route within a network

Circuit: the conduit over which data travels

Key Data Communication Terminology
Packetizing: 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

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

Networks- Why we need Them?
Point to point communication not usually practical

Devices are too far apart
Large set of devices would need impractical number of connections
Networks- Why we need Them?
Solution is to connect all devices to a central system known as a NETWORK

Two Main Classes of Networks
Local Area Networks (LANs)
Wide Area Network (WANs)
Networks
Distributed Processing

Network Criteria

Physical Structures

Categories of Networks
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”

Advantages of Distributed Processing
Security
Distributed Data bases
Faster Problem Solving
Security through Redundancy
Collaborative Processing


Network Criteria
Network Criteria
Performance

Number of Users
Type of Transmission Medium
Hardware
Software
Network Criteria
Reliability

Frequency of failure
Recovery Time after Failure
Catastrophe
Network Criteria
Security

Unauthorized Access
Viruses
Network Applications
Marketing and Sales
Financial Services
Manufacturing
Electronic Messaging
Teleconferencing
Cable Television

Simplex
Half-duplex
Full-duplex
Point-to-point connection
Multipoint connection
Categories of topology
Fully connected mesh topology (for five devices)
Star topology
Bus topology
Ring topology
Categories of networks
LAN
LAN (Continued)

MAN

WAN
The Internet
A Brief History

The Internet Today
Internet today
Protocols and Standards
Protocols

Standards

Standards Organizations

Internet Standards
Protocols

“Set of Rules Governing Communication”
Protocols
Protocols defines:

What is Communicated?
How, it is Communicated?
When, it is Communicated?
Protocols
Elements of a Protocol:
Syntax
Semantics
Timing
Standards
“A standard provides a model for development that makes it possible for a product to work regardless of the individual manufacturer”

Why Standards are Essential?
Standards are essential in:

Creating/Maintaining Open and Competitive Markets

Guaranteeing National/International Interoperability

Why Standards are Essential?
Categories of Standards
Standards Organizations
Standards are developed mainly by 3 entities:

Standard Committees
Forums
Regulatory Agencies

Standard Creation Committees
The International Standards Organization (ISO)

The International Telecommunication Union-Telecommunications Standard Sector
   (ITU-T)
The American National Standard Institute (ANSI)

The Institute of Electrical and Electronics Engineers (IEEE)

Standard Creation Committees
FORUMS
Frame Relay Forum
ATM Forum
Internet Society
Internet Engineering Task Force (IETF)
Regulatory Agencies
FCC
LINE CONFIGURATION
“Line Configuration refers to the way two or more devices attach to a link”

  
LINE CONFIGURATION
Point-to-Point Line Configuration
Multipoint Line Configuration

Communications Channels

A communications channel is a pathway over which information can be conveyed. It may be defined by a physical wire that connects communicating devices, or by a radio, laser, or other radiated energy source that has no obvious physical presence. Information sent through a communications channel has a source from which the information originates, and a destination to which the information is delivered. Although information originates from a single source, there may be more than one destination, depending upon how many receive stations are linked to the channel and how much energy the transmitted signal possesses.

In a digital communications channel, the information is represented by individual data bits, which may be encapsulated into multibit message units. A byte, which consists of eight bits, is an example of a message unit that may be conveyed through a digital communications channel. A collection of bytes may itself be grouped into a frame or other higher-level message unit. Such multiple levels of encapsulation facilitate the handling of messages in a complex data communications network.

Any communications channel has a direction associated with it:
The message source is the transmitter, and the destination is the receiver. A channel whose direction of transmission is unchanging is referred to as a simplex channel. For example, a radio station is a simplex channel because it always transmits the signal to its listeners and never allows them to transmit back.

A half-duplex channel is a single physical channel in which the direction may be reversed. Messages may flow in two directions, but never at the same time, in a half-duplex system. In a telephone call, one party speaks while the other listens. After a pause, the other party speaks and the first party listens. Speaking simultaneously results in garbled sound that cannot be understood.

A full-duplex channel allows simultaneous message exchange in both directions. It really consists of two simplex channels, a forward channel and a reverse channel, linking the same points. The transmission rate of the reverse channel may be slower if it is used only for flow control of the forward channel.

data communication and networking

The distance over which data moves within a computer may vary from a few thousandths of an inch, as is the case within a single IC chip, to as much as several feet along the backplane of the main circuit board. Over such small distances, digital data may be transmitted as direct, two-level electrical signals over simple copper conductors. Except for the fastest computers, circuit designers are not very concerned about the shape of the conductor or the analog characteristics of signal transmission.

Frequently, however, data must be sent beyond the local circuitry that constitutes a computer. In many cases, the distances involved may be enormous. Unfortunately, as the distance between the source of a message and its destination increases, accurate transmission becomes increasingly difficult. This results from the electrical distortion of signals traveling through long conductors, and from noise added to the signal as it propagates through a transmission medium. Although some precautions must be taken for data exchange within a computer, the biggest problems occur when data is transferred to devices outside the computer's circuitry. In this case, distortion and noise can become so severe that information is lost.

Data Communications concerns the transmission of digital messages to devices external to the message source. "External" devices are generally thought of as being independently powered circuitry that exists beyond the chassis of a computer or other digital message source. As a rule, the maximum permissible transmission rate of a message is directly proportional to signal power, and inversely proportional to channel noise. It is the aim of any communications system to provide the highest possible transmission rate at the lowest possible power and with the least possible noise.