Business Data Communications,
Fourth Edition
Chapter 8: Wide Area and
Metropolitan Area Networks
Learning Objectives
• Describe the topologies used in wide area
networks and metropolitan area networks
• Explain the use of IBM’s System Network
Architecture (SNA) and how it relates to
today’s communications environments
• Define Systems Application Architecture
(SAA) and how it is used in a wide area
network
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Learning Objectives
• Describe the use of Digital Network
Architecture (DNA)
• Illustrate the differences among the
layered architectures of SNA, SAA, DNA,
and the OSI model
• Explain the concepts of electronic
commerce and business-to-business
initiatives
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Learning Objectives
• Explain how electronic data interchange
(EDI) uses wide area networks
• Describe the use of metropolitan area
networks in the corporate environment
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Introduction
• Wide area networks are used to connect remote
devices
• Provides connections between customers and
suppliers, WANs and LANs
• Remote programmers connected to mainframe
computers via WANs
• Global networks
• Metropolitan area networks use some LAN
technologies and some WAN technology
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Network Connections
• Point-to-Point Connections
– Server to client
– Remote clients
– Computer to computer
– Console system terminals
– Channel – connects FEP to server
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Network Connections
• Multipoint Connections
– Many remote clients connected to a server
– Modem and/or concentrator used
– Less costly than point-to-point
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Figure 8-4. Multipoint Lines.
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Topologies
• Wide Area Network Topologies
– Hierarchical Topology
•
•
•
•
•
Used in traditional mainframe networks
Looks similar to an organization chart
Server (mainframe) at top
Several layers below
Used in large corporate networks
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Topologies
• Wide Area Network Topology
– Star Network
• Central node is the server
• All clients connected through point-to-point lines
• Private Branch Exchange (PBX) is example
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Topologies
• Wide Area Network Topology
– Ring Networks
• Servers in the WAN are connected in a ring
• Local environment may be other topologies
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Topologies
• Metropolitan Area Network Topologies
– Larger than LANs, smaller than WANs
– Bus Topology
• Single wire connecting all devices
• Uses either fiber optic or coaxial cable
– Ring Topology
• Uses Fiber Distributed Data Interface (FDDI)
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Systems Network Architecture
• IBM product
• Used on S/390 systems
• Used hierarchical topology (called a
subarea network)
• Peer networks now supported as well
• IBM developed the standards for WAN
architectures
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Systems Network Architecture
• Advanced Program-to-Program
Communication (APPC)
– Used for peer networks
– AKA LU 6.2
– Describes a common set of protocols used
across multiple systems
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Systems Application
Architecture
• Standards for use among many types of IBM computers
• Facilitates Enterprise Computing
• Has three characteristics:
– Common User Access (user interface)
– Common Programming Interface for Communications (programs
run on different platforms)
– Common Communications Support (multiple systems can
communicate effectively)
• The SAA Layered Model
– Deals only with software, so no physical layer exists
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Digital Network Architecture
• Architecture used by Digital Equipment
Corporation computers (now Compaq)
• Has evolved over the years to a peer network
• DNA Structured Model
– Has eight layers
– Many hardware platforms need to communicate
• Enterprise Virtual Intelligent Switched Networks
(enVISN) Architecture
– Open network architecture
– A look to the future of networks
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Electronic Commerce
• Building business relationships over the Internet
• Storefront retailers often now have Web sites to
sell products
• Requirements to participate
– Web address
– Server
– Technical support personnel
• Security of on-line transactions
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Data Warehousing
• Collection of data from many sources
– Legacy systems
– On-line systems
– New client/server systems
• Data mining
– Finding information my getting more details about a particular
subject
• Provides fast access to data
• Applications
– Corporate data
– AOL Moviefone – movie information
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Business-to-Business (B2B)
Initiatives
• Retailers buying from wholesalers
• Many B2B initiatives using the Internet
• Examples
– US Office Products
• Direct link to their supplier (United Stationers)
– BOC Group
• Customers build orders based on contracts,
patterns are supplied to make ordering easier
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Electronic Data Interchange
• Exchange of orders/invoices directly between
two computers
• Components of EDI
– Computer
– Network
– Software
• Application Program – Order entry, accounts payable, etc.
• Network Software – Delivers data to proper system
• Translation Software – Converts data to a form that the
application program recognizes
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Electronic Data Interchange
• eXtensible Markup Language (XML) and
EDI
– Internet Programming Standard
– Allows different computers to exchange data
– Allows easy manipulation of data
– XML defines the content of the data
– Will complement EDI in the future
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Electronic Data Interchange
• Components of EDI
– Need a computer, a connection to a network,
software
– Types of software
• Application program
• Network software
• Translation software
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Electronic Data Interchange
• EDI Standards
– ANSI X.12
• Defines data fields
• Used in the United States
– Electronic Data Interchange for
Administration, Commerce, and Transport
(EDIFACT)
• Used in Europe and Canada
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Electronic Data Interchange
• Advantages of EDI
– Reduces the amount of paper generated
– Reduces cost of transactions
• Physical documents cost more than electronic
ones
• Eliminates re-entry of data
• Mailing costs are reduced
– Faster transmission of document
– Fewer data-entry errors
– Security of documents is better
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Metropolitan Area Network
Implementations
• MAN Layered Architecture
– Similar to layered model for LANs
– Uses only the bottom two layers of OSI model
• Municipal MAN
– Connect offices throughout a city
• School District MAN
– Connects schools and administrative offices
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Summary
• WANs used to connect
computers, terminals,
LANs
• Point-to-point versus
multipoint connections
• Topologies
• SNA designed for WANs
by IBM
• SAA used as common
interface and
programming language
among platforms
Chapter 8: Wide Area and Metropolitan Area Networks
• DNA is Digital
Equipment’s layered
architecture
• Electronic commerce and
data warehousing are
used more widely in
today’s business
environment
• EDI connects suppliers
and customers via WANs
• Metropolitan area
networks have many
applications in different
environments
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Summary
• DNA is Digital Equipment’s layered architecture
• Electronic commerce and data warehousing are
used more widely in today’s business
environment
• EDI connects suppliers and customers via
WANs
• Metropolitan area networks have many
applications in different environments
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