IST 220-002:
Networking and Telecommunications
Chapter 1: Introduction to
Computer Networks & Data Communication
Dr. Lee Giles
001 Thomas Building, School of IST
Phone 865 7884
Email: giles@ist.psu.edu
1
What is Information Technology (IT)?
Information Technology (IT)
Computer
Technology
To collect, store, process,
search, retrieve, and present
electronic information to
meet the needs of various
kinds of users, e.g., computer
hardware & software, PDAs,
printers, groupware, smart
cards….
Communication
Technology
To deliver, disseminate,
exchange, transmit, and
receive electronic information
in local, regional or global
contexts, e.g., networks, fax
machines, cell phones, email,
satellites, GPS, Internet,
telephony, ….
2
Computer Systems Redefined
Computer systems used to be defined as:
hardware +
software
Computer systems are now redefined as:
hardware +
software
+ networks
3
Information & Communication
 Generation and transfer of information
is critical to today’s businesses
 Flow of information both mirror and
shape organizational structures
 Networks are the enabling technology
for this process
4
The “Manager’s Dilemma”
 Technology is necessary for
competitiveness
 Cost of technology has decreased
 Reliance on technology has increased
 Number of choices have increased
 Choices are both more difficult and
more important
5
What is Data Communication?
 Communication of data between sources
 Data formats – analog or digital or both
 Data travels by a medium
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
Wires
Space
6
Essentials of Data Communication
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Message
Sender
Receiver
Medium
Understandability
Error detection
Security
7
Types of Messages
8
Protocols
 Enables communication – how we
communicate (convention used for
establishing transmission rules)

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
When
Where
How
What with
How much
9
Protocols
10
Important Dates in the History of
Data Communications (1)
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1837 – Invention of the telegraph
1876 – Invention of the telephone
1947 – Invention of the transistor (replaced vacuum tubes)
1948 – First commercial computer installed, the UNIVAC I
1958 – First U.S. Communications satellite sent into orbit
1959 – FCC approves private microwave communications
networks
 1964 – Packet switching network concept proposed by the
Rand Corporation
 1966 – IBM's binary synchronous (BISYNC or BSC)
protocol announced
 1969 – ARPANET, first packet switching network (later to
become the Internet), begins operation
11
Important Dates in the History of
Data Communications (2)
 1972 – Ethernet local area network specifications formulated
 1972 – IBM's Synchronous Data Link Control (SDLC) protocol
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

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announced
1974 – IBM announces its Systems Network Architecture (SNA)
1975 – Personal computers introduced, the Altaire 8800 replaced
terminals in many cases
1981 – IBM PC introduced
1985 – Cellular radio telephones are introduced
1990 – World Wide Web is introduced
1993 – Web search engines introduced
1995 – The Internet grows to over four million host computers
1999 – The Internet grows to over ten million host computers
12
Data Communication Applications (1)
 Batch - bi-directional transfers of large
amounts of data in concentrated groups
 Data Entry - Lengthy inputs with short
responses
 Distributed - data and/or processing is
handled by more than one processing
unit
 Inquiry/Response - Small inputs of data
that may result in large responses
13
Data Communication Applications (2)
 Interactive - Short inputs and outputs.
Real-time response with direct user
interaction
 Sensor-Based - Input derived from
sensors instead of human operators
 Combined - More than one of the above
applications running at the same time
14
What is a Computer Network?
Two or more computers or communications devices connected
by transmission media and channels and guided by a set of rules
for communication purposes that allow users to communicate
with each other and share applications and data.
Hardware:
Computer
Network card
Routers
Modem …
Media:
Cable
Wire
Microwave …
Components of a Computer Network
Software:
Network OS
Utilities …
Network Design:
Logical layout
Physical layout …
15
Applications of a Computer Network
 Mass transit
 Interstate highways
 24-hour bankers, grocery stores
 Cable television
 Pagers
 Mobile telephones
 Most businesses and schools
 Retail outlets
…
16
Network Essentials
Models
•Client/Server
Technologies
•Ethernet
•Token Ring
•Transmission Control
Protocol/Internet
Protocol (TCP/IP)
•Wireless Application
Protocol (WAP)
•Peer-to-Peer
Network OS
Topologies
Types
•Local Area Network
(LAN)
•Metropolitan Area
Network (MAN)
•Wide Area Network
(WAN)
•Bus Topology
•Ring Topology
•Star Topology
17
Network Technologies
Ethernet
Token Ring
TCP/IP
WAP
 Based on bus topology; but can be used in star topology;
 Higher speed: first Fast Ethernet, then Gigabit Ethernet;
 Most popular: inexpensive, easy to install and maintain.
 Based on a ring topology; but can use a star topology;
 Token-passing scheme to prevent collision of data;
 The second most widely-used protocol after Ethernet.
 Based on client/server model of network computing;
 Uses packet switching technique for data transmission;
 Commonly used for Internet applications.
 Uses client/server model of network computing;
 Allows wireless devices to access the Internet and WWW;
 Meets increasing demands for wireless Internet access.
18
The World of Connectivity
Wired or wireless communications
links offer several options for
information and communications.
Source: The McGraw-Hill Companies, Inc., 1999
19
Computer Network Configurations:
Connections between Networks
 Computer terminal to mainframe computer
 Microcomputer to mainframe computer
 Microcomputer to local area network
 Microcomputer to Internet
 Local area network to local area network
Local area network to wide area network
Sensor to local area network
Satellite and microwave
Wireless telephone
20
Computer Network Configurations:
Computer Terminal to Mainframe Computer
Used in many types of businesses for data
entry and data retrieval.
Usually involves a low-speed connection.
21
22
Computer Network Configurations:
Microcomputer to Local Area Network
Very common throughout business and
academic environments.
Typically a medium- to high-speed
connection.
23
24
Computer Network Configurations:
Microcomputer to Internet
Very popular with home users.
Typically a modem is used to connect user’s
microcomputer to an Internet Service
Provider.
Newer technologies such as DSL and cable
modems are replacing
modems.
25
26
Computer Network Configurations:
LAN to LAN Connections
Found in businesses and schools that have
two or more LANs and a need for them to
intercommunicate.
The bridge is a typical device used to
interconnect LANs.
27
Data Communications and Computer Networks
Chapter 1
28
Computer Network Configurations:
LAN to WAN Connections
One of the best ways to interconnect a user
on a workstation to the Internet (a wide area
network).
A router is the typical device that performs
LAN to WAN connections.
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30
Computer Network Configurations:
Sensor to LAN Connections
Often found in industrial environments.
Assembly lines and robotic controls depend
heavily on sensor-based local area networks.
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Computer Network Configurations:
Satellite and Microwave
Many types of applications including long
distance telephone, television, radio, longhaul data transfers, and wireless data
services.
Typically expensive services but many
companies offer competitive services and
rates.
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Computer Network Configurations:
Wireless Telephone
Quickly expanding market across the U.S.
and world.
First generation analog services and second
generation PCS services available in most
areas and under many types of plans.
Third generation services beginning to appear
in Europe and Asia.
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Why Are Networks Important?
•Enterprise
•Organization
•Department
•Individual
Users
•LANs
•Mans
•WANs
Internet
Network
BUSINESS
ENTERPRISE
•Wired
•Wireless
Information
•Traditional Data
•Text
•Images
•Graphics
•Voice
•Video
•Multi-media
Applications
•Functions
•Organizational
Processes
•Personal
Networks: Pros and Cons
Pros
Resource sharing

Printers, CD-ROMs, computers
Data and information sharing
Communications
Reduced Cost
On-line services
Groupware

Cons
Security risks increase with
networks
Complexity is associated with
networks
Investment is high and return
on it may not happen
Software that supports group efforts
over a network
Electronic data interchange
38
Key Issues of Networks
Access to the Internet
Network Access

Wired access
 Cable modem
 DSL

Wireless access
 Wireless LAN

RosettaNet – XML based
Network security

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Goals and Measures
Firewalls
39
Why Use a Network?
 Sharing of
 Data, messages, graphics …
 Applications …
 Devices, e.g., hard drives, backups, printers,
modems, fax machines …
 Centralized administration
 Installing and upgrading application software
 Communication and collaboration
 Teleconferences, group decision support systems
40
Class Discussion
 If you could design your own home, what
kinds of computer network or data
communications labor-saving devices would
you incorporate?
 Using a laptop computer with a wireless
connection into the company’s local area
network, you download a Web page from the
Internet. List all the different network
configurations involved in this operation.
41
Language of Computer Networks
 Important terms and concepts.
42
Components of a Network
 Server
 A computer that provides services to other networked computers
 Client
 A computer in a client/server relationship, e.g., a Web browser
 Hardware/Software
 Network card, router, modem, hub/NT operating systems, utilities
…
 Media
 The way to connect computers on a network
 Data
 Files o be shared by network computers
 Resources
 Peripherals, e.g., printers, to be used by network computers
43
Media of Networking
 Coax cable
 Twisted pair cable
 Fiber optic cable
 Microwave
 Communications satellite
 Cellular phones
44
Networking Hardware
Workstations
Servers
Bridges
Routers
Hubs and switches
Nodes
45
Network Models
Client/Server Model
Microcomputer users, or
clients, share services of
a centralized computer
called a server.
Peer-to-Peer Model
Computers share equally
with one another without
having to rely on a
central server.
46
Client/Server
A distinction exists between computers that make available network resources
(servers) and those computers that use the resources (clients or workstations).
Pros:
 Very secure
 Centralized servers easy to manage
 Physically centralized
 Secure OS
 Better performance
 Centralized backups
 Reliability
 Simple job to do plus built in redundancy
Cons:
 Require professional administration
 More hardware intensive
47
Peer-to-Peer (p2p)
Computers on the network communicate with each others as equals and each
computer is responsible for making its own resources available to other
computers on the network.
Pros:
 Uses less expensive computer networks
 Easy to administer
 No NOS (network operating system) required
 More built-in redundancy
 Shared resources – some machine will have what you need
Cons:
 Individual user performance easily affected
 Not very secure
 Tragedy of the commons – no guarantee others will administer their
resources properly (almost guaranteed with over 10 machines)
 Hard to back up.
48
Client/Server vs. Peer-to-Peer:
Advantages and Disadvantages
Client/Server Model
Peer-to-Peer Model
Advantages:
Advantages:
 Very secure OS.
 Better performance.
 Centralized servers, easy
to manage.
 Centralized backups.
 High reliability.
 Uses less expensive networks.
 Easy to administer.
 Contain both network operating
system and application software.
 Ideal for small business and home
users.
Disadvantages:
 Expensive administration.
 More hardware intensive.
Disadvantages:
 Individual user performance easily
affected.
 Not very secure.
 Hard to back up.
49
Networking Essentials
 Computer Networks
 A host computer connected with communication circuits
and equipment to terminals
 Two or more computers connected via a communication
medium
 Intranet
 A private version of the Internet
 Enterprise Network
 Two or more LANs connected to each other, or one or more
LANs connected to a WAN
 File Server
 A computer that contains files shared by PCs on a network
50
Categorization of Networks
 By size:
 Wide Area Network (WAN)
 Metropolitan Area Network (MAN)
 Local Area Networks (LAN)
 By capability:
 Client/server
 Peer-to-peer
51
Three Major Types of Networks
 Local Area Network (LAN)
 Serves users within a confined geographical area
(usually within a mile).
 Metropolitan Area Network (MAN)
 Covers a geographic area the size of a city or
suburb. The purpose of a MAN is often to bypass
local telephone companies when accessing longdistance service.
 Wide Area Network (WAN)
 Covers a wide geographical area, such as a state or
a country. Examples: Tyment, Telenet, Uninet, and
Accunet.
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Interconnection between LANs and WANs
53
Characteristics Differentiate
One Network from Another
Topology : The geometric arrangement of devices on
the network. For example, devices can be arranged in
a ring or in a bus or in a star topology.
Protocols : The rules and encoding specifications for
sending data. The protocols also determine whether
the network uses a peer-to-peer or client/server
model.
Media : Devices can be connected by twisted-pair
wire, coaxial cables, or fiber optic cables.

Wireless networks are connected via radio waves.
Medium Access Control: Scheme to allow sharing
of the media.
54
Components of a Typical LAN
Source: The McGraw-Hill Companies, Inc., 1999
55
Network Typologies: Star
This arrangement connects all the network’s devices to a central
host computer, through which all communications must pass.
Source: The McGraw-Hill Companies, Inc., 1999
56
Network Typologies: Ring
This arrangement connects the network’s devices in a closed loop.
Source: The McGraw-Hill Companies, Inc., 1999
57
Network Typologies: Bus
A single channel connects all communications devices.
Source: The McGraw-Hill Companies, Inc., 1999
58
Networking and Telecommunications
Networking - an interconnection of computers
and computing equipment using either wires
or radio waves over small or large geographic
distances
Telecommunications - study of telephones
and the systems that transmit telephone
signals
Network management - design, installation,
and support of a network and its hardware and
software
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Networking Aspects
 Computer Networks
 A host computer connected with communication circuits and
equipment to terminals
 Two or more computers connected via a communication medium
 Intranet
 A private version of the Internet
 Enterprise Network
 Two or more LANs connected to each other, or one or more
LANs connected to a WAN
 File Server
 A computer that contains files shared by PCs on a network
60
Network Selection Criteria
 Size of the organization
 Level of required security
 Level of available administrative support
 Amount of network traffic
 Needs of the network users
 Budget for building the network
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Requirements of a Network System (1)
 Ideal system

Does what we want instantly when we want it
with no errors or problems and only we know
about it.
 Performance
 Consistency
 Flexibility
 Availability
 Reliability
 Recovery
 Security
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Requirements of a Network System (2)
 Performance

Response time
 Time for transmission
 Time for data processing

Transaction Rate (throughput)
 The amount of work performed by a system per unit
of time
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Requirements of a Network System (3)
Consistency


Same thing all the time
Response time
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Requirements of a Network System (4)
 Flexibility
Growth and change available with
minimum impact on users
 Legacy systems
 Standards help

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Requirements of a Network System (5)
 Availability
When needed
 Where available
 How available

66
Requirements of a Network System (6)
 Reliability

Measure of system failure
 MTBF – mean time between failure

Fault-tolerance solution
 Design
 Duplication
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Requirements of a Network System (7)
Recovery
 All systems fail
 How long before startup?

What do we get when the system starts up again
 Saved information
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Requirements of a Network System (8)
 Security
 Who has access?
 How good is the protection?
 Privacy
69
Network Architecture Models
A reference model that describes the layers of
hardware and software necessary to transmit
data between two points.
Reference models are necessary to increase
the likelihood that different components from
different manufacturers will converse.
There are two standard models that are
important: The OSI Model, and the Internet
Model.
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Standards
Standards are rules of operation that are
followed by most or all vendors
Standards allow hardware and software
from different vendors to work together
Competition among vendors brings
lower prices and feature-rich products
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Standards
ISO - International Standards Organization:
An organization that sets communication
standards, also IEEE
OSI - Open Systems Interconnection: A
seven layer reference model for developing
data communication systems
Open Architecture - in which the network
specifications are available to any company
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OSI Layers of Communication
73
Application Layer
 Where the application using the
network resides. Common network
applications include remote login, file
transfer, e-mail, and web page
browsing.
 Functionality defined by user
 Application dependent
74
Presentation Layer
 Performs a series of miscellaneous
functions necessary for presenting the
data package properly to the sender or
receiver
 Format of the data
 Encryption
 Compression
 Screen formatting
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Session Layer
 Establishes connection between
applications
 Enforces rules
 Order
 Pacing
 Reestablish connection
76
Transport Layer
 Provides an end-to-end, error-free
network connection.
 Makes sure the data arrives at the
destination exactly as it left the source.
 Makes sure all information is accounted
for:


Missing information
Duplicated information
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Network Layer
 Responsible for creating maintaining
and ending network connections.
 Transfers a data packet from node to
node within the network.
 Message routing
 Billing
 Accounting
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Data Link Layer
 Responsible for taking the data and
transforming it into a frame with header,
control and address information.
 Physical path communication
 Error detection
 Error correction
 Resolve competing requests
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Physical Layer
 Handles the transmission of bits over a
communications channel.
 Includes:






Voltage levels
Electrical connections
Media choices
Adapters
Connectors
Modulation techniques
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Layers in Internet Model vs. OSI Model
 Interface layer - equivalent to the OSI’s
physical and data link layers.
 Network layer - roughly equivalent to the
OSI’s network layer.
 Transport layer - performs same function as
OSI transport layer.
 Application layer - equivalent to the OSI’s
presentation and application layers.
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The Internet Model vs. the OSI Model
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Internet Model in Action
 Note the flow of data from user to web
browser and back.
 At each layer, information is either added or
removed, depending on whether the data is
leaving or arriving at a workstation.
 The adding of information over pre-existing
information is termed encapsulation.
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Logical and Physical Connections
 A logical connection is one that exists
only in the software
 A physical connection is one that exists
in the hardware.
 In a network architecture model, only
the lowest layer contains a physical
connection, while all higher layers
contain logical connections.
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OSI Layers of Communication
87
Software Environment
 Application Programs
 Word, Excel, Access, Lotus 123, etc.
 Operating System
 Manages the resources of the computer. (E.G. Windows 98/NT, Linux)
 Data Communication
 Responsible for handling communication with remote devices
 Transaction Control Process

Receives input and routes it to the proper application processes
 Database Management System
 Interface between the application programs and the data they need to use.
 Transaction Processing
 Responding to requests for processing activities. The requests are usually
user initiated but may be made by other systems
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IT Infrastructure
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Class Discussion
 How have you used a network today.
 Discuss an example of a business that incorporates
layers of management and show how the work
progresses through the layers.
 Are there any network configurations that have not
been addressed in the chapter? What are their
applications?
 Are there any other examples in business where
one particular technology or method has won out
over the competition? What were the reasons that
lead to this particular technology winning? 90
Joining Professional
Associations
Benefits can include:
Connecting with people who have
similar interests
Providing new opportunities for learning
Allowing access to specialized
information
Giving tangible assets such as free
goods
Professional Association Sites
TABLE 1-2
Web sites of
networking
organizations
Circa 2000.
Some do not
exist today!