Education purpose

1. 1.1
Chapter 1
Introduction

2. 1.2
1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS
The termThe term telecommunicationtelecommunication means communication at ameans communication at a
distance. The worddistance. The word datadata refers to information presentedrefers to information presented
in whatever form is agreed upon by the parties creatingin whatever form is agreed upon by the parties creating
and using the data.and using the data. Data communicationsData communications are theare the
exchange of data between two devices via some form ofexchange of data between two devices via some form of
transmission medium such as a wire cable.transmission medium such as a wire cable.
Components
Data Representation
Data Flow
Topics discussed in this section:Topics discussed in this section:

3. 1.3
Figure 1.1 Five components of data communication

4. 1.4
Data Representation
Information today comes in different forms such as text,
numbers, images, audio, and video.
Text: In data communications, text is represented as a bit
pattern, a sequence of bits (Os or 1s). Different sets of bit
patterns have been designed to represent text symbols.
Each set is called a code, and the process of representing
symbols is called coding. (ASCII, Basic Latin)
Numbers are also represented by bit patterns. However, a
code such as ASCII is not used to represent numbers; the
number is directly converted to a binary number to simplify
mathematical operations.

5. 1.5
Data Representation
Images are also represented by bit patterns. In its simplest
form, an image is composed of a matrix of pixels (picture
elements), where each pixel is a small dot. The size of the
pixel depends on the resolution.(Red, Green, Blue), (Yellow,
Cyan, and magenta).
Audio refers to the recording or broadcasting of sound or
music. Audio is by nature different from text, numbers, or
images. It is continuous, not discrete.
Video refers to the recording or broadcasting of a picture or
movie. Video can either be produced as a continuous entity
(e.g., by a TV camera), or it can be a combination of images,
each a discrete entity, arranged to convey the idea of
motion.

6. 1.6
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

7. 1.7
1-2 NETWORKS1-2 NETWORKS
AA networknetwork is a set of devices (often referred to asis a set of devices (often referred to as nodesnodes))
connected by communicationconnected by communication linkslinks. A node can be a. A node can be a
computer, printer, or any other device capable of sendingcomputer, printer, or any other device capable of sending
and/or receiving data generated by other nodes on theand/or receiving data generated by other nodes on the
network.network.
Distributed Processing
Network Criteria
Physical Structures
Network Models
Categories of Networks
Interconnection of Networks: Internetwork
Topics discussed in this section:Topics discussed in this section:

8. 1.8
Distributed Processing
Most networks use distributed processing, in which a task is
divided among multiple computers. Instead of one single
large machine being responsible for all aspects of a
process, separate computers (usually a personal computer
or workstation) handle a subset.

9. 1.9
Network Criteria
To be considered effective and efficient, a network must
meet a number of criteria.
Performance
Reliability
Security

10. 1.10
Performance can be measured in many ways, including transit
time and response time. The performance of network depends
on a number of factors.
Number of users : Having a large number of concurrent users
can slow response time in a network not designed to coordinate
heavy traffic loads. In peak load periods the actual number of
users can exceed the average and decrease performance.
Type of transmission medium : The medium defines the
speed at which data can travel through a connection (the data
rate). The speed of light imposes an upper bound on the data rate.
Connected Hardware : The types of hardware included in a
network affect both the speed and capacity of transmission.
PerformancePerformance

11. 1.11
Software : The software used to process data at the sender,
receiver and intermediate nodes also affects network performance.
PerformancePerformance

12. 1.12
ReliabilityReliability
Network reliability is measured by frequency of failure, the
time it takes a link to recover from failure, and the network’s
robustness in a catastrophe.
Frequency of failure : All networks fail occasionally. A
network that fails often is of little value to a user.
Recovery time of a network after a failure : How long does
it take to restore service? A network that recovers quickly is
more useful than one that does not.
Catastrophe : Networks must be protected from catastrophic
events such as fire, earthquake, or theft.

13. 1.13
Network security issues include protecting data from
unauthorized access and viruses.
Unauthorized Access : For a network to be useful, sensitive
data must be protected from unauthorized access. Protection can be
accomplished at a number of levels.
Viruses : Because a network is accessible from many points, it
can be susceptible to computer viruses. A virus is an illicitly
introduced code that damages the system.
SecuritySecurity

14. 1.14
Figure 1.3 Types of connections: point-to-point and multipoint

15. 1.15
Figure 1.4 Categories of topology
The Topology of a network is the geometric representation of
the relationship of all the links and linking devices (usually
called nodes) to one another.

16. 1.16
Every device has a dedicated point-to-point link to every
other device.
n(n-1)/2 physical channels to link n devices.
Advantages:
Dedicated Links, Privacy or Security, Fault Identification and
Fault isolation.
Disadvantage:
Amount of Cabling, Number of I/O Ports.
Mesh topology

17. 1.17
Figure 1.5 A fully connected mesh topology (five devices)

18. 1.18
Figure 1.6 A star topology connecting four stations

19. 1.19
Each devices has a dedicated point-to-point link only to a
central controller, usually called a hub. The devices are not
directly linked to each other.
Advantage:
Less expensive then mesh topology, Easy to install and
reconfigure, Robustness
Disadvantage:
More cabling then some other topologies(such as tree, ring,
bus). If central point fails, the entire network goes down.
Star topology

20. 1.20
Figure 1.7 A bus topology connecting three stations

21. 1.21
The bus topology is also known as a linear bus. This is the
simplest and most common method of networking computers. It
consist of a single cable called a trunk that connects all of the
computers in the network in the single-line.
Advantages:
Easy to install, Less cabling then mesh star or tree
Disadvantages:
Difficult reconfiguration and fault isolation
A fault or break in the bus cable stop all transmission.
A bus topology

22. 1.22
Figure 1.8 A ring topology connecting six stations

23. 1.23
The ring topology connects computers on a single circle of
cable. There are no terminated ends.
Each computer like a repeater to boost the signal and it on to
the next computer.
Advantagess:
Easy to install and reconfigure, Fault isolation is simplified
Disadvantages: In a simple ring, a break in the ring can disable
the entire network.
Ring topology

24. 1.24
Figure 1.9 A hybrid topology: a star backbone with three bus networks

25. 1.25
Categories of Networks
A LAN normally covers an area less than 2 miles; a
WAN can be worldwide. Networks of a size in between
are normally referred to as metropolitan-area networks
and span tens of miles.

26. 1.26
 LANs are designed to allow resources to be shared between personal
computers or workstations. The resources to be shared can include hardware
(e.g., a printer), software (e.g., an application program), or data.
 The switched WAN connects the end systems, which usually comprise a
router (internet working connecting device) that connects to another LAN or
WAN. The point-to-point WAN is normally a line leased from a telephone or
cable TV provider that connects a home computer or a small LAN to an Internet
service provider (ISP). This type of WAN is often used to provide Internet
access.
 A good example of a MAN is the part of the telephone company network that
can provide a high-speed DSL line to the customer. Another example is the
cable TV network that originally was designed for cable TV, but today can also
be used for high-speed data connection to the Internet.
Categories of Networks

27. 1.27
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

28. 1.28
Figure 1.11 WANs: a switched WAN and a point-to-point WAN

29. 1.29
Interconnection of Networks: InternetworkInterconnection of Networks: Internetwork
Today, it is very rare to see a LAN, a MAN, or a LAN inToday, it is very rare to see a LAN, a MAN, or a LAN in
isolation; they are connected to one another. When two orisolation; they are connected to one another. When two or
more networks are connected, they become anmore networks are connected, they become an
internetwork, or internet.internetwork, or internet.

30. 1.30
Figure 1.12 A heterogeneous network made of four WANs and two LANs

31. 1.31
1-3 THE INTERNET1-3 THE INTERNET
TheThe InternetInternet has revolutionized many aspects of our dailyhas revolutionized many aspects of our daily
lives. It has affected the way we do business as well as thelives. It has affected the way we do business as well as the
way we spend our free time. The Internet is away we spend our free time. The Internet is a
communication system that has brought a wealth ofcommunication system that has brought a wealth of
information to our fingertips and organized it for our use.information to our fingertips and organized it for our use.
Advanced Research Projects Agency (ARPA)
The Internet Today (ISPs)
Topic discussed in this section:Topic discussed in this section:

32. 1.32
 The Advanced Research Projects Agency (ARPA) in
the Department of Defense (DoD) was interested in
finding a way to connect computers so that the
researchers they funded could share their findings,
thereby reducing costs and eliminating duplication of
effort.
In 1967, at an Association for Computing Machinery
(ACM) meeting, ARPA presented its ideas for ARPANET,
a small network of connected computers.
The idea was that each host computer (not necessarily
from the same manufacturer) would be attached to a
specialized computer, called an interface message
processor (IMP). The IMPs, in turn, would be connected to
one another. Each IMP had to be able to communicate
with other IMPs as well as with its own attached host.
Advanced Research Projects Agency (ARPA)

33. 1.33
The Internet TodayThe Internet Today
Today most end users who want Internet connection useToday most end users who want Internet connection use
the services of Internet service providers (ISPs). Therethe services of Internet service providers (ISPs). There
are international service providers, national serviceare international service providers, national service
providers, regional service providers, and local serviceproviders, regional service providers, and local service
providers. The Internet today is run by private companies,providers. The Internet today is run by private companies,
not the government.not the government.

34. 1.34
Figure 1.13 Hierarchical organization of the Internet
NAP -> Network Access Points

35. 1.35
1-4 PROTOCOLS AND STANDARDS1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms:In this section, we define two widely used terms: protocolsprotocols
andand standardsstandards. First, we define protocol, which is. First, we define protocol, which is
synonymous with rule. Then we discuss standards, whichsynonymous with rule. Then we discuss standards, which
are agreed-upon rules.are agreed-upon rules.
Protocols
Standards
Standards Organizations
Internet Standards
Topics discussed in this section:Topics discussed in this section:

36. 1.36
Protocol is a set of rules that govern data communication. A
protocol defines what is communicated, how is communicated,
and when is communicated. Key elements of protocol are:
• Syntax: refers to the structure or format of the data, meaning
the order in which they are presented.
• Semantics : refers to the meaning of each section of bits.
How is a particular pattern to be interpreted, and what action is
to be taken based on that interpretation?
• Timing : refer to two characteristics. When data should be
sent and how fast they can be sent.
ProtocolsProtocols

37. 1.37
Standards are essential in creating and maintaining an
open and competitive market for equipment manufacturers
and in guaranteeing national and international
interoperability of data and telecommunications technology
and processes.
Standards provide guidelines to manufacturers, vendors,
government agencies, and other service providers to
ensure the kind of interconnectivity necessary in today's
marketplace and in international communications.
StandardsStandards

38. 1.38
1. De facto. Standards that have not been approved by an
organized body but have been adopted as standards
through widespread use are de facto standards. De
facto standards are often established originally by
manufacturers who seek to define the functionality of a
new product or technology.
2. De jure. Those standards that have been legislated by
an officially recognized body are de jure standards.
Data communication standards fall into two categories:
de facto (meaning "by fact" or "by convention") and
de jure (meaning "by law" or "by regulation").

39. 1.39
Standards are developed through the cooperation of
standards creation committees, forums, and government
regulatory agencies.
 Standards Creation Committees
international Organization for Standardization
International Telecommunication Union
Telecommunication Standards Sector(ITU-T)
American National Standards Institute (ANSI)
Institute of Electrical and Electronics Engineers (IEEE)
Electronic Industries Association (EIA)
Standards Organizations

40. 1.40
To accommodate the need for working models and
agreements and to facilitate the standardization process,
many special-interest groups have developed forums made
up of representatives from interested corporations. The
forums work with universities and users to test, evaluate, and
standardize new technologies.
Forums

41. 1.41
All communications technology is subject to regulation by
government agencies such as the Federal Communications
Commission (FCC) in the United States. The purpose of
these agencies is to protect the public interest by regulating
radio, television, and wire/cable communications.
Regulatory Agencies