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Business Data Communications,
Fourth Edition
Chapter 7: Network Concepts
Learning Objectives
• Define the terms used when describing a
network and its components
• List the differences among circuitswitching, message-switching, packetswitching, and cell-switching networks
• List the types of routing techniques used
to move data through a network
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Learning Objectives
• Describe the difference between a public
network and private network
• Illustrate the difference between a LAN
and a WAN
• Describe the functions of the Internet and
intranets
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Learning Objectives
• Describe the characteristics that
distinguish a distributed network from
other types of networks
• List the types of distributed processing
• Describe the types of files used in
distributed systems
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Introduction
• Basic concepts and terminology are needed for
a foundation of the study of networks
• Network switching and routing is critical to
network operation
• Network ownership
• Types of networks
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LANs
WANs
Internet
Intranets
Distributed Networks
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Basic Network Concepts
• Network – the interconnection of devices
for communications
• Servers (hosts) – independent computer
systems
• Node – device with a network address
• Link – connection between adjacent nodes
• Path – series of links
• Circuit – End-to-end connection (made up
of links and paths)
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Chapter 7: Network Concepts
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Chapter 7: Network Concepts
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Chapter 7: Network Concepts
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Networking Techniques
• Non-switched network – Point-to-point link
• Switched Networks – Nodes
interconnected
– Circuit-Switching
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Dedicated path
Entire circuit must be available
Telephone network
Inefficient for data transmission
Used for intermittent data transmission
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Chapter 7: Network Concepts
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Networking Techniques
• Switched Networks
– Message-switching
• No dedicated circuit required
• Messages pass through many nodes to the
destination
• Store-and-forward technique used
• Similar to post office mail delivery
• Some delays in delivery may occur
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Chapter 7: Network Concepts
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Networking Techniques
• Switched networks
– Packet-switching
• Similar to message-switching, but uses a fixed-size
message, called a “packet”
• All packets are the same length
• Network performance is much better than on a
message-switching network
• Pipelining used
– Instructions are available as soon as necessary to the
receiving computer
– Provides faster execution time
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Chapter 7: Network Concepts
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Chapter 7: Network Concepts
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Networking Techniques
• Switched Networks
– Packet-switching – Types
• Datagram services – each packet treated
independently
• Switched Virtual Circuit (SVC) – logical connection
established prior to transmission
• Permanent Virtual Circuit (PVC) – permanent
circuit, no call setup is needed
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Networking Techniques
• Switched Networks
– Cell-switching
• Used in Asynchronous Transfer Mode (ATM)
networks
• Cell-based network
• Cell is 53 bytes long
• Uses a virtual circuit
• More in Chapter 13
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Networking Techniques
• Broadcast Networks
– Use radio waves
– Packet radio network
– National Weather Service uses it to gather
information from remote sites
– Also used on the U.S. Space Shuttle and the
International Space Station (ISS)
– Special modem is used
– Uses the AX.25 protocol and TCP/IP
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Routing
• Computers use routing to send data to the
correct destination
– Centralized routing
• One node is the network routing manager
• Central point of failure
• Routing information may be far from central node
– Distributed routing
• Each node contains a routing table
• Increased traffic on network due to sending updates to other
nodes
– Routing table used to determine best route
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Chapter 7: Network Concepts
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Routing
• Types of Routing
– Static routing
• Same route used from source to destination
• Route is fixed
• Data may not arrive if path is blocked
– Dynamic (adaptive) routing
• Route changes based on conditions on the network
• The network software selects the best route
– Broadcast routing
• Transmit to all nodes in the network (flooding)
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Chapter 7: Network Concepts
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Network Ownership
• Private network
– Built by a company for its own use
• Public network
– Built and owned by common carrier
– Telephone network, ISPs, AOL
• Virtual Private Network (VPN)
– Private network that uses public carrier lines
• Packet distribution network (PDN)
– Use X.25 protocol
– Packet-switching technology on public or private networks
– Provide high-speed lines between nodes
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Network Types
• Local Area versus Wide Area Networks
– Local Area Network (LAN)
• Nodes in a small area
– Campus, office, building
• Widely used
• Owned entirely by the organization in which it resides
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Network Types
• Local Area versus Wide Area Networks
–Wide Area Network (WAN)
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Nodes over a large area
Often uses common carrier lines
Originally developed for mainframe networks
Many functions taken over by LANs
Still exist for many applications
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Chapter 7: Network Concepts
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Network Types
• The Internet and Intranets
– Internetwork (internet)
• Refers to networks that are connected
– Internet (uppercase I)
• A specific, named network
• World Wide Web
– Intranet
• Uses Internet technology on an internal network
• Company calendars and forms may be posted
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Chapter 7: Network Concepts
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Network Types
• The Internet and Intranets
– Access
• Internet – open to anyone with proper access
• Intranet – used only by selected people
• Firewall – allows only authorized access to a network
– Applications
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Web pages (viewed using a Web browser)
John Deere (conversion of legacy systems)
Federal Express (customer access to shipping information)
Olivetti (employee collaboration over the Web)
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Distributed Systems
• Evolution from centralized to distributed systems
• Definition of Distributed Systems
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Systems with independent processing capability
Spread across multiple locations
Processors function independently
Components: hardware, operating system software,
application software, data
– Control is centralized or distributed
– Data is centralized or distributed
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Distributed Systems
• Characteristics of Distributed Systems
– Use smaller computers rather than large,
centralized systems
– Increased user involvement
– Modular – an individual component can be
easily replaced
– User response time is faster
– System is more flexible (uses many
manufacturer’s equipment)
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Chapter 7: Network Concepts
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Distributed Systems
• Types of Distributed Systems
– Distribution by Location
• Hardware at many different geographic locations
• Uses a network to communicate
• Functions such as backup may not be done as
required, due to lack of training
• On-site specialists may be needed
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Chapter 7: Network Concepts
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Distributed Systems
• Types of Distributed Systems
– Distribution by Function
• Specific computers at different sites do different
functions for the corporation
• Individual departments have their own computers,
isolated from other departments
• May cause problems if data needs to be shared
among departments
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Chapter 7: Network Concepts
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Distributed Systems
• Types of Distributed Systems
– Distribution by Control
• Refers to management of programmers and data
• Creation of application programs may need to rely
on data from another department
• Systems need to work together
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Distributed Systems
• Types of Distributed Systems
– Distribution by Processing
• System designed around how data is processed
• Processing of data is done at many sites
• Hierarchical distributed system (Vertical system)
– Some processing on central computer, some done at a
remote, smaller computer
• Horizontal distributed system (Peer computers)
– Computer systems are equal
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Chapter 7: Network Concepts
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Distributed Systems
• Implementation of Distributed Systems
• File Handling
– Distributed File System (DFS) is software used
– Location independence means any application
program can access data, no matter where it resides
– Different architectures and operating systems must
allow access to the data
– Must overcome contention on the network for file
access
– Security of the file is also handled by the DFS
– Maintains file directory of all files in system
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Distributed Systems
• Data Distribution
– Data may be stored in files or databases
– Single storage site in centralized configuration
– Copies of data kept at remote sites
– Local computers may have independent file
systems
• May create inconsistent data
• Must synchronize all data periodically
• Separate data systems cannot share data
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Distributed Systems
• Distributed Databases
– Database – group of related data
• Data is used by many applications
• Reduces amount of redundant data stored
– Database Management System (DBMS)
• Software that controls the database
• Logical versus physical records
– Directory of data is needed to locate data
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Chapter 7: Network Concepts
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Distributed Systems
• Incompatibility Problems
– Multiple databases can cause problems
– Format of data and data names must be known
throughout the distributed system
– Conference on Data Systems Languages
(CODASYL)
• Standards for DBMSs
• Not used by all manufacturers
– Different types of databases
• DL/I language to access data
• Relational database – uses a matrix to access data
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Summary
• Learn about networks by knowing network
definitions
• Switching techniques used in modern
networks
– Circuit-switching, message-switching, packetswitching, cell-switching
• Routing decisions made on a network
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Summary
• Private and public networks differ in
ownership
• Local area networks in a small area
• Wide area networks in a wide geographic
area
• Internet versus intranets
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Summary
• Systems can be distributed by location,
function, and control
• Hierarchical and horizontal systems exist
• Data integrity must be maintained
• Distributed systems can use databases
• Distributed systems require the use of
networks
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Chapter 7 Complete