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McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004
Chapter 1
Introduction
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Chapter 1
At the end of the discussion, students will be
able to identify the fundamental characteristics
of a data communication system.
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Data communications and networking is changing we do business and the
way we live.
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1.1 Data Communication
Components
Data Representation
Direction of Data Flow
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TELECOMMUNICATION
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Figure 1.1 Simple Network Diagram
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Delivery System must deliver the data to the
correct destination Accuracy
System must deliver the data accurately Timeliness
System must deliver the data in timely manner
Jitter Variation in the packet arrival time.
Data communication fundamental characteristics
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Message Information (data) to be communicated.
Sender Device that sends the data message.
Transmission Medium Carries data.
Receiver Device that receives the message.
Protocol Set of rules that govern data
communication.
Five components of data communication
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Figure 1.1 Five components of communication system
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Information today comes in different forms.
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Text Represented as a bit pattern
Numbers Also represented as a bit pattern
Images Composed of a matrix of pixels
Audio Recording or broadcasting of sound or
music Video
Recording or broadcasting of picture or movie
Data Representation
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Communication between two devices can be either simplex, half-duplex and
duplex.
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Simplex
In simplex mode, the communication is unidirectional.
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Half-duplex
In half-duplex mode, each station can both transmit and receive, but not at the same time.
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Full-duplex
In full-duplex mode both stations can transmit and receive simultaneously
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1.2 Networks
Distributed ProcessingNetwork CriteriaPhysical StructuresCategories of Networks
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A network is a set of devices (called as nodes) connected by communication
links.
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Distributed processing is the division of tasks in a network among its
computers.
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A network must meet a certain number of criteria: performance, reliability
and security.
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Performance Depends on a number of factors,
including transit time, response time, number of users, type of transmission medium, throughput and delay.
Reliability Measured by the frequency of failure, the
time it takes a link to recover and the network’s robustness in catastrophe.
Security Includes protecting data from
unauthorized access, protecting data from damage and development, etc.
Network Criteria
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A network is two or more devices connected through links.
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Point-to Point (P2P) Provides a dedicated link between two
devices.
Types of Connection
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Multipoint (P2MP) More than two specific devices share a
single link. Also called multidrop/broadcast connection.
Types of Connection
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Physical topology refers to the way in which a network is laid out physically.
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Mesh topology Every device has a dedicated point-to-
point link to every other device.
Basic Topologies
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ExampleExample
Consider a mesh network with 6 nodes, calculate how many cable connections needed in order to have a complete mesh configuration?
# of links = 6 (6 - 1) / 2 = 15 links# of links = 6 (6 - 1) / 2 = 15 links
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Mesh topology Advantage:
Dedicated links guarantees own data load Robust Privacy/Security Easy fault isolation
Disadvantage Amount of cabling and no. of I/O ports
required Difficult installation and reconnection Expensive
Basic Topologies
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Star topology Each device has a dedicated point-to-point link
only to a central controller, usually called a HUB.
Basic Topologies
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Bus topology One long cable acts as a backbone to
link all the devices in a network
Basic Topologies
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Ring topology Each device has a dedicated point-to-point
connection with only the two devices on either side of it.
Basic Topologies
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Ring topology Advantage:
Orderly Performs better than bus topology Does not require network server
Disadvantage Failure of a single node, failure of entire
network Sensitive to node changes
Basic Topologies
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Hybrid (Tree) topology The topology in which a central 'root' node is
connected to one or more other nodes that are one level lower in the hierarchy.
Basic Topologies
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Star topology Advantage:
Easy to install and reconfigure Less cabling needed Robust Simplicity of operation
Disadvantage Dependency on one single point Possible slow down of network
Basic Topologies
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Hybrid (Tree) topology Advantage:
Supported by hardware vendors P2P connection is possible Ease of node access
Disadvantage Length of network depends of the type of
cable Entirely dependent on the trunk Difficult to configure
Basic Topologies
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Bus topology Advantage:
Easy to implement and extend Easy to install Cost effective Simplicity of operation
Disadvantage Difficult reconnection and fault isolation Dependency on the bus Limited cable length and number of stations
Basic Topologies
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Chapter 11. What is the difference between audio to
text, numbers and images? 2pts
2. What are the 3 characteristics of a network?
3. Consider a mesh network with 7 nodes, calculate how many cable connections needed in order to have a complete mesh configuration?
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The category into which a network falls is determined by its size.
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Local Area Network (LAN) connects nodes in a limited
geographical area normally covers an area less than 2 mi. e.g. home, school, computer lab, office
bldg. uses Ethernet cables, switches and hubs
Categories of Networks
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Metropolitan Area Network (MAN) larger than a LAN but smaller than a
WAN normally covers a town or a city connects nodes for high-speed
connectivity e.g. DSL internet connection, cable
internet connection
Categories of Networks
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Wide Area Network (MAN) spans a large physical distance Internet is the largest WAN is not owned by any one organization use technology like ATM, Frame Relay
and X.25
Categories of Networks
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Heterogeneous Network
Categories of Networks
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Interconnection of Networks:
Internetwork
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History 1960’s US government seeks nuclear war proof
communications, created ARPA 1969 Universities and researches connected to
ARPAnet In 1972, Vinton Cerf and Robert Kahn
collaborated for the Internetting Project In 1977 ARPAnet engineers devised a
communication protocol known as TCP/IP 1983 ARPAnet switched to TCP/IP 1989 Tim Berners-Lee proposes a new set of
Internet protocols 1995 US government releases Internet for
commercial use
Internet
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A protocol is a set of guidelines or rules.
A technical standard is an established norm or requirement.
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Protocols rules determining the format and
transmission of data key elements of a protocol:
syntax semantics Timing/synchronization
Protocols and Standards
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Standards provide guidelines to create and maintain an
open competitive market categories:
De Facto De Jure
Standards Creation Committees International Organization for Standardization (ISO) International Telecommunication Union (ITU) Consultative Committee for International Telegraphy
and Telephony (CCITT) American National Standard Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Electronics Industries Association (EIA)
Protocols and Standards
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Standards Forums
made up of representatives from interested corporations
test, evaluate and standardized new technologies present their conclusion to standards bodies
Regulator Agencies communication technology is regulated by
government agencies protect public interest by regulating radio, TV & cable Federal Communications Commission (FCC) - USA National Telecommunication Commission (NTC) - PHIL
Protocols and Standards
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End of Chapter 1
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Chapter Questions:Q.1) Which of the following are types of computer networks? A. LAN, NAN, WAN B. WAN, ring, star, bus C. old boys' network, old girls' network, business associates D. extranet, intranet, LAN, WAN Q.2) Which of the following is the best description of the transmission directions possible in a network? A. simplex, half-duplex, full duplex B. simplex, half-duplex, full duplex, duplex C. half duplex, 2/3 duplex, full duplex D. duplex, half duplex, 1/4 duplex Q.3) Which of the following is NOT a list of network topologies? A. star, bus, ring B. star, ring, hybrid C. bus, ring, double ring, hexagon D. ring, mesh, star, bus, Q.4) Which network topology has a central device which brings all the signals together? A. bus B. star C. ring D. hybrid Q.5) Which network topology requires terminators at the ends of the lines? A. ring B. bus C. star D. mesh Q.6) A blank is a number of computers linked together to allow them to share data and/or other resources. ( 2 words or 1 word )
Q.7) All communication systems must have a sender, a receiver and a blank. ( 2 words or 1 word ) Q.8) What is being described here -> pairs of copper wires twisted around each other. ( 3 words or 2 words )
Q.9) This cable uses light to transmit data instead of magnetic signals. ( 3 words or 2 words or 1 word ) Q.10) A blank converts digital signals to analogue signals and also analogue signals to digital signals . ( 1 word )
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Chapter Questions:
1. Identify the five properties of a data communications system.
2. Name four basic network topologies, and cite an advantage of each.
3. Why are protocols needed?