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Chapter 1
Introduction
1.1
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1-1 DATA COMMUNICATIONS
The term telecommunication means communication at
a distance.
The word data refers to information presented in
whatever form is agreed upon by the parties creating and
using the data.
Data communications are the exchange of data between
two devices via some form of transmission medium such
as a wire cable.
Topics discussed in this section:
Components
Data Representation
Data Flow
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The effectiveness of a data communications system
depends on Four fundamental characteristics:
• Delivery
• Accuracy
• Timeliness
• Jitter
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Components
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Data Representation
Data
Text
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Numbers
Image
Audio
Video
Data Flow
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1-2 NETWORKS
A network is a set of devices (often referred to as nodes)
connected by communication links.
A node can be a computer, printer, or any other device
capable of sending and/or receiving data generated by
other nodes on the network.
Topics discussed in this section:
Distributed Processing
Network Criteria
Physical Structures
Network Models
Categories of Networks
Interconnection of Networks: Internetwork
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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 handle a subset.
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Network Criteria
Performance
- Measured in many ways, including transit time and response time.
- The performance of a network depends on a number of factors,
Including number of users, type of transmission medium, capabilities of
the connected hardware, and the efficiency of the software.
-Performance are usually evaluated by two networks metrics:
Throughput and Delay.
Reliability
Measured by the frequency of failure, the time it takes a link to recover
from failure.
Security
Include protecting data from unauthorized access, from damages, and
implementing policies and procedures for recovery from data looses.
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Physical Structure
Type of connection
a) Point-to-point (P2P)
• Detected Links between two devices
• Entire capacity is reserved for transmission between two devices
• Could be wired or wireless
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Physical Structure
Type of connection
a) Multipoint
•More than two devices share a single link.
•The capacity of the channel is shared (spatially/temporally)
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Physical Structure
Physical Topology
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Physical Structure
Physical Topology
a) Mesh
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• Dedicated p2p
•Number of links depends on
duplex mode
•Advantages
- no traffic problems
- it is robust
- privacy
- fault isolation
•Disadvantages
- wiring
- I/O requirements
Physical Structure
Physical Topology
b) Star
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• Devices are connected through
a hub (p2p)
• No direct traffic between
devices
• Advantages
- less wiring
- fault isolation
• Disadvantages
- centralized
- traffic
Physical Structure
Physical Topology
c) Bus
•Point to multipoint
•Advantages: - easy to install. - cheap
•Disadvantages: - no fault isolation.
- limited.
- quality due to connectors
- fault can cause noise
- congestion
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Physical Structure
Physical Topology
d) Ring
• Point to point
• every device is connected to its neighbor on either sides
•Repeater is used
• simple/dual ring
•Token ring (no collision)
•Advantages: (easy to install/ fault isolation (alarm))
•Disadvantages: (no fault isolation/ limited/ quality due to connectors/
fault can cause noise/ congestion)
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Physical Structure
Physical Topology
e) Hybrid
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Network Model
Computer networks are created by different entities.
Standards are needed so that these heterogeneous
networks can communicate with one another.
The two best-known standards are OSI model and
the Internet model.
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Categories on Network
 LAN
networks connect a single office, building, campus
WAN
network connect countries, the world
MAN
network connect areas inside cities
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Categories on Network
LAN
•LAN size is limited to few km
•Used to share resources
• usually server based
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Categories on Network
WAN
• Provide long distance
transmission
•Internet is example
•Switched/p2p
•X.25/ATM
•WiMax
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Categories on Network
MAN
A metropolitan area network (MAN) is a network with a
size between a LAN and a WAN.
• It normally covers the area inside a town or a city
• 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.
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Interconnection of Network: Internetwork
• When 2 or more network connected together it becomes an
internetwork or internet
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1-3 THE INTERNET
The Internet has revolutionized many aspects of our daily
lives.
It has affected the way we do business as well as the way
we spend our leisure time.
The Internet is a communication system that has brought a
wealth of information to our fingertips and organized it for
our use.
The Internet is a structured, organized system.
Topics discussed in this section:
A Brief History
The Internet Today (ISPs)
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A Brief History
A network is a group of connected communicating devices.
An internet is two or more networks communicate together.
The most notable internet is called (Internet).
In 1960, mainframes was standalone devices , the Advanced
Research Project Agency (ARPA) start the first computer
connection.
In 1967, at ACM, ARPA presents ARPANET.
In 1969, reality of ARPANET.
In 1972, Vint Cerf and Bob Kahn produced the Internet
Project.
TCP splitted into two protocols: TCP and IP.
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The Internet Today
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1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms:
protocols and standards.
 First, we define protocol, which is synonymous with rule.
Then we discuss standards, which are agreed-upon rules.
Topics discussed in this section:
Protocols
Standards
Standards Organizations
Internet Standards
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Protocols
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A protocol is a set of rules that govern data communications. A
protocol defines what is communicated, how it is
communicated, and when it is communicated. The key
elements of a protocol are syntax, semantics, and timing.
Syntax refers to the structure or format of the data, meaning
the order in which they are presented.
Semantics. The word 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. The term timing refers to two characteristics: when
data should be sent and how fast they can be sent.
Standards
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Standards are essential in guaranteeing national and
international interoperability of data and telecommunications
technology and processes. Standards provide guidelines
De facto standards -> by manufacturers
De jure standards -> by government
Standards Organization
Standard Creation Committee
•International Organization for Standardization (ISO).
•International Telecommunication Union –
Telecommunication Standard Sectors (ITU-T).
•American National Standard Institute (ANSI).
•Institute of Electrical and Electronic Engineers (IEEE).
•Electronic Industries Association (EIA).
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Internet Standards
•It is a thoroughly tested specification that is useful to and
adhered to by those who work with the Internet.
•There is a strict procedure by which a specification attains
Internet standard status.
•An Internet Draft is a working document with no official
status.
•A draft may be published as a Request for Comment
(RFC).
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