Introduction to Networking
Data Communications and NetworksMr. Greg VoglUganda Martyrs UniversityLecture 2, 19 March 2003
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Overview1. Definitions
1. LAN/WAN, Internet/Intranet, Client/Server/Peer
2. Local Area Networks1. Types, components, topologies, resources2. Benefits/costs, design questions
3. Wide Area NetworksA. Connecting networksB. Models, componentsC. Benefits/costs
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LAN vs. WAN Network
connection of computers so they can exchange data and share resources
LAN: Local Area Network link computers within a small geographic area,
such as a building or a group of buildings uses direct cables (or wireless signals)
WAN: Wide Area Network powerful computers linked across large
distances uses wires, cables, electromagnetic signals, etc.
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Internet vs. Intranet Internet
a global network of networks that connects millions of computers
Intranet a private version of the Internet,
using Web browsers and server on LANs
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Client-Server vs. Peer-to-Peer Server
computer that provides access to shared resources
e.g. printers and disks Client
computer accessing shared resources on servers Client-Server Network
one or more computers dedicated as servers many clients
Peer-to-Peer Network shares resources among a few “equal” computers
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Client-Server Networks Dedicated server computers provide resources Client computers access server’s resources Centralised administration and maintenance Requires highly trained network administrator Security is strong, user and group-based Performance depends on server capabilities Works well for large networks (>10 computers)
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Peer-to-Peer Networks Each computer acts as both client and server No server computer or network OS required Distributed administration and maintenance Users must act as administrators of their PCs Security is weak, resource-based Performance depends on peer workstations Best for small network of <10 advanced users
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LAN Hardware Components Computers: two or more, maybe a server Hub: at least one, with one port per computer NICs: Network Interface Cards/Adapters
One installed in each computer, connects to hub Cables: to connect computers
Unshielded twisted pair (UTP), co-axial, fibre optic Peripherals: to be shared on the network
Printers, scanners, disk drives, modems, etc.
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Network Operating Systems Peer-to-Peer
Windows 3.11/95/98/Me Windows NT/2000 Pro
Client-Server Windows NT/2000 Server Novell Netware UNIX/Linux
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Terminology Topology
physical layout of network connections Protocol
standard of how devices communicate Interface
connection to allow communication Bandwidth or Data Transfer Rate
data speed in bits per second
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Network Topologies: Star Each computer is attached to central
hub Easy to add/remove computers
connect cable to computer and to hub port
Bad cable only isolates one computer Hub is single point of failure Most popular for LANs
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Network Topologies: Bus Each computer attached to the
network cable Cheapest (no hub required) Difficult to add/remove computers Difficult to troubleshoot bad
connections Broken connection partitions network Sometimes used for small LANs
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Network Topologies: Ring Computers connected in a closed loop Token of data passed around in one
direction Often logical ring but physical star
Multi-station access unit (MSAU) hub Fibre distributed data interface (FDDI)
Used to connect high-speed networks
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Sharing Resources Resources that can be shared include:
hardware (disks, printers, scanners, fax...) software (programs) data (files, folders) servers: file, print, directory, mail, fax
Access to resources can be restricted: to certain users or groups (with NT Server) read-only password-protected
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Network Neighborhood Accessible through Desktop, My
Computer or Windows Explorer Shows computers in local area
network Computers are grouped into
workgroups or domains Each computer lists its shared
resources
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LAN Benefits Shared resources (hardware, software,
data) Economy of scale: low cost per user/computer
Communication and information exchange Email, Web browsing, conferencing, scheduling,
etc. Centralised, remote administration
Install, backup, monitor, cleanup, troubleshoot
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LAN Costs Network hardware Network OS Communications software Network design and development Administration and maintenance Training Security
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Client/Server Costs
Operations and support Application development Hardware, software Network installation, maintenance Education and trainingSource: Laudon & Laudon, Table 9.5
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Networking Problems
Connectivity problems Loss of management control Ogranizational changes required Hidden costs Network reliability and securitySource: Laudon & Laudon, Table 9.4
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Network Design Questions Who are your users? What are their individual and group goals? What are their computing/information
needs? What types of uses will the computers have? What software do they need to use? What hardware is needed to run the
software? What data traffic is the network likely to
have?
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Network Design Questions (cont’d) Is a dedicated server needed? What server specifications will be
needed? Is a network operating system needed? What backup media should be used? What shared resources should be
available? How should access to resources be
restricted? Other security problems/measures?
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Connecting Networks
Intranet Private version of Internet; protected by firewall
Extranet Intranet accessible to authorised outsiders
Virtual Private Network Secure Internet connection for data transmission
Internetworking Linking separate networks
Enterprise Network A network to link a company’s resources
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Connectivity Models
TCP/IP model Developed by US Defense Dept; used on Internet Five layers: physical, net, IP, TCP, application Every Internet site has an IP address
Open Systems Interconnect (OSI) model Developed by International Standards Org. for linking different types of computers, networks Seven layers, idealised, rarely implemented fully public, nonproprietary, portable
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WAN Hardware Components Gateway
Connects different types of networks by translating
Bridge Connects similar networks
Router Intelligently directs traffic to appropriate
networks Routes data packets through connected
LANs/WAN
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Communications Hardware Telephones, modems, PBX, voice mail,
Facsimile/Fax Information digitised, transmitted through phone
lines Cellular (mobile) phones, pagers
Wireless communication using radio waves Videoconferencing
Computers, video cameras, microphones, speakers Global Positioning System (GPS)
Satellites determine position of devices Used for tracking and navigation of vehicles, etc.
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Communications Software Personal Info. Management e.g. MS Outlook
Address book, notes, messages, task lists Scheduling (calendar, meetings, appointments, etc.)
Groupware e.g. Lotus Notes Scheduling, e-mail, conferencing, editing, databases
Project Management e.g. MS Project Planning, scheduling, analysing Tasks, events, resources, costs
Other e.g. dial-up networking, terminal emulators Connect to computers/networks, transfer files, run
programs
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Internet Components Network hardware and operating systems
to send/receive information over long distances Web pages
hypertext documents (linked together) multimedia (pictures, sounds, videos etc.)
Web server Computer that stores web documents
Web clients Browser software to retrieve and view web pages mail, newsgroups, chat, conferencing, file
transfer
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Internet Access Internet Service Provider (ISP)
Organisation with direct Internet connection Sells Internet connections to
businesses/individuals Providers of online services: AOL, MSN,
Prodigy Internet Café
Pays ISP to connect its LAN to Internet Allows individuals to use Internet for short
periods
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Internet Benefits to Organisations Connectivity and global reach Reduced communication costs Lower transaction costs Reduced agency costs Interactivity, flexibility, customization Accelerated distribution of knowledgeSource: Laudon & Laudon, Table 10.2
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Intranet Benefits
Easy to build and run; inexpensive Easy to update, expand or contract Easy to access by different
PCs/devices Easy to use (Web browser is familiar) Multimedia, interactive, responsive Reduced info. distribution costsSource: Laudon & Laudon, Table 10.6