CIS 209 Data Communications
Chapter 1 Lecture Notes
Text: Business Data Communications Sixth Edition – Stamper, Case
Chapter 1 Introduction to Data Communication
Goals
 Differentiate between data communications and telecommunications
 Identify the essential elements of communication.
 Identify the essential features of networks.
 Discuss network requirements.
 List the seven layers of the OSI reference model.
 List the five layers of the TCP/IP protocol stack.
 Discuss several significant events in the history of data communications.
 Identify and briefly describe several business data communications applications.
 Discuss several business data communications issues.
 Identify business data communications occupation and career options.
What is Data Communications?
The transmission of data to and from computers and components of computer systems.
The subset of business telecommunications that addresses the processes, equipment,
facilities, and services used to transport data from devices at one location to devices at
other locations.
Essential Features of Communication
 Message
Types of data communication messages include:
file - group of related items
request - from sender to receiver for some action to be performed
response - from receiver back to sender
status - status of the system (e.g. system going down in 5 minutes)
control - sent between system components (e.g. printer out of paper)
correspondence - sent from user to user
 Sender
Originator of the message, either a person or a machine.
 Receiver
Destination of the message.
 Medium
Where the message physically travels to get from sender to receiver.
 Understandability
A message must be understood before communications has taken place.
 Error Detection
How to determine if the message was changed during transmission.
Essential Features of Networks
Network – At least one sender and one receiver connected by a communication medium.
Session – The exchange of messages between two users over a network.
Node - Device that is connected to a network
Link - The circuit between two adjacent nodes, with no intervening nodes.
Path - One or more links that allows a message to travel from sender to receiver
Circuit - Either the medium connecting two devices or a path
Virtual Circuit – A temporary communications path created between two nodes in a
switched communication network.
Packetizing – Dividing a message into packets prior to transmitting the message over a
communication medium.
Packet Switching - The transmission of a message by dividing the message into fixedlength packets and then routing the packets to the recipient. Packets may be sent over
different paths and arrive out of order.
Routing - How the path from sender to receiver is determined
Store-and-Forward - The messages are stored at intermediate nodes and then forwarded
to the next node.
Network Topology - The physical form the network takes
Network Architecture - The way in which media, hardware, and software are integrated
to form a network.
User - Any originator of a message
OSI Reference Model
International Standards Organization (ISO) – An organization that is active in setting
electronics, electrical, and data communication standards.
To help understand the OSI reference model, consider how a worker might send a
message from their office to a colleague in another location.
(See page 12, steps 1 - 8).

Functions of OSI Layers
Application - Application dependent
Presentation - Formats the data. Handles: encryption, compression, terminal
screen formatting, and conversion from one transmission code to another (such as
EBCDIC to ASCII)
Session - Establishes the connection, reestablishes the connection if a failure
occurs, and handles flow control.
Transport - Ensures that all packets of data have been received by the destination,
that there are not duplicates, and that packets are ordered in the proper sequence.
Network - Does message routing and collects billing and accounting information.
Data Link - Establish and control the physical path of communication to the next
node. This includes error detection and correction, defining packet size, and
resolving requests for shared communication link.
Physical - Specifies the electrical connections between the transmission medium
and the computer system.
History of the Telecommunication Industry
Telegraph
The first American telegraph line, completed in 1843, went
from Baltimore to Washington, a distance of 37 miles. The
first message, "What hath God wrought?," was sent by the
system's inventor, Samuel Morse, on May 24, 1844. By then,
Morse had perfected the system of dot and dash telegraph
signals that became known as Morse Code. The telegraph
completely revolutionized American communications.
Messages could be sent instantly, and newspapers,
businesspeople, and even ordinary citizens embraced the new
technology. The telegraph played a key role in the Civil War
as well. For the first time, distantly located officers and even
President Lincoln himself could receive timely reports from
the battlefield and use them to plot strategy.

1876 Alexander Graham Bell Invention of the telephone
From this early drawing of the
first telephone, sketched out by
Alexander Graham Bell, a new
technology that many
considered no more than a
curious toy blossomed into one
of the most ubiquitous forms of
technology ever conceived.

1890s Tesla / Marconi development of wireless communication
History of Data Communication
 The Transistor
1947 Brattain, Bardeen, and Shockley at Bell Laboratories
 The Hush-a-Phone Case
1948 court case, 1956 appeals court. First non AT&T equipment allowed to
connect to the telephone.
 Competition for Long-Distance Transmission
1963 MCI filed with the FCC to provide microwave communication services
between Chicago and St Louis.
 The Carterphone Case
1966 court case. First non AT&T equipment allowed to connect to the telephone
network.
 Local Area Networks
Computers located within a small geographic area linked together in order to
share data.
 Wide Area Networks
Computers separated by large distances linked together in order to share data.
 Data Link Protocols
Govern the flow of data between sending and receiving stations.
 Microcomputers
Introduced in 1975 with the Altaire 8800. Used to replace terminals in many
cases.
 The Internet
A specific collection of interconnected networks spanning nearly all the countries
of the world.. Began in 1969 as the Arpanet.
 The Telecommunications Act of 1996
More deregulation of the telecommunications industry. Allows more competition
among communication services.
Data Communication Applications
 E-Mail – At first simple text. Now text, graphics, audio, image, and video.
 Voice Applications – Today, voice and data communication are being integrated
into one system. ISDN and voice-over IP both send voice as digital data.
 Groupware – Allows a group of users to work collaboratively. (calendar systems,
filing cabinets, project management, decision support systems, electronic meeting,
document management)
Other Data Communication Applications
 Batch Applications
Typically, bi-directional transfers of large amounts of data in concentrated groups.
 Data Entry Applications
Lengthy inputs with short responses.
 Distributed Applications
The data and/or processing is handled by more than one processing unit.
 Inquiry/Response Applications
Small inputs of data that may result in large responses.
 Interactive Applications
Short inputs and outputs. Real-time response with direct user interaction.
 Sensor-Based Applications
Input derived from sensors instead of human operators.
 Combined Applications
More than one of the above applications running at the same time.
Business Data Communications Issues
 Cost-Effectiveness
The bottom line in a business is profit. Data communications helps improve
profits by:
- resource sharing
- better communication may improve productivity
- less paperwork

The Internet
- Online sales
- Marketing of products for conventional sales channels
- support
- direct communication with other corporate entities anywhere in the world

Bandwidth
- the capacity of a communications link
- measured in bits per second (bps) or bytes per second (Bps)
- bandwidth determines the time required to send data

Evolving Technologies
- to be competitive businesses must monitor and evaluate new technologies

Convergence
- the blending of communications and computing technologies

Standards
- standards allow equipment from different manufactures to work together
- without standards the communications equipment would be more expensive
and more difficult to use.

Privacy and Security
- more channels of communication means more possible security problems for
corporations.
- Hackers
- Employee theft
- Employee privacy issues
- Viruses
Requirements of an Online System
 Performance
Response Time - The interval between entering a message and getting the
response.
Throughput - The amount of work performed by a system per unit of time.
 Consistency
A consistent system has response times that are similar for all transactions
 Flexibility
The ability to have both growth and change with minimal impact on existing
applications and users.
 Availability
The system is ready when the user needs it.
 Reliability
The probability that a system will continue to function.
MTBF - Mean Time Between Failures. The average time until a system can be
expected to fail.
MTTR - Mean Time To Repair. The average time required to repair a system.
 Recovery
The act of restoring a system to operational status following a failure.
 Security
Security does not prevent unauthorized access to a system, but makes it more
difficult.