Networks 1 Introduction to Networks Dr John Cowell phones off
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Overview Introduction to networks what is a network, why? basic
types of networks Geographical descriptions LAN, MAN, WAN
Intranets, extranets and the Internet definitions 2
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What is a Network? A network is a communication system a
collection of resources hardware & software objects people
Varying types of network computer telephones Any two or more
interconnected computer systems can be described as a network
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Why use a Network? Improve communications team working Share
resources hardware software data Central services Efficiency 5
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Types of Networks There are several different types of networks
Depends on connectivity geographic area covered topology/protocol
Connectivity peer to peer client / server distributed system three
tier architecture 6
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Peer to Peer Simplest is peer-to-peer, connected via
serial/parallel ports RS 232 null modem cable 7
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Windows Peer-to-Peer Windows allows creation of larger
peer-to-peer networks, using network protocols resources, e.g.
printers, modems, attached to one PC, but can be shared by other
users Use Control Panel/Networks to configure 8
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Client / Server As number of users / workstations increases, it
is more efficient to create a client / server network Multiple
workstations connected to one or more network servers file server
print server communications server fax server 9
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Client / Server Communication Clients and servers can also be
viewed as being software applications Interact by using one of
several methods message passing remote procedure calls
Synchronicity is important i.e. server cannot process until client
has sent request client passes values to server, then waits server
processes values, returns results asynchronous relationship Servers
may have higher network priority access to otherwise restricted
system resources 10
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Servers 1 File server shared data can be stored and managed
centrally access can be controlled/logged Print server multiple
printers can be connected to server server organises print queues
Network printers direct connection to network 11
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Servers 2 Communications server acts as interface between
network and outside world other networks the Internet Fax server
faxes are a different technology to email, etc server handles user
requests to send faxes 12
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Distributed Systems Physically separate computers in a network
operate together as a single logical unit Beowulf clusters Appears
to a user to be a single computer physically separated an operating
system that supports distributed systems is required, e.g. UNIX
advantages include reduction in costs and delays in transmitting
and processing data reduced load on the host processor better local
control and service 13
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Three Tier Architecture Client / server model has some problems
not scaleable business rules not deployed centrally consumes too
many resources on client machine inefficient One proposed solution
is to partition applications into logical parts each part can have
multiple units 14
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Three Tier Model The three parts are 15 user services front end
application data services database engine business logic Controls
interaction between a Database and a user interface
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Three Tier Benefits Four major benefits (are claimed) reuse
components are shared between applications time in design and
implementation not wasted maintenance as business changes,
modifications in applications and business rules are easier to
implement performance optimised as individual components can be
upgraded manageability complex application is broken down into
smaller components easier to work with 16
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Geographical Network Areas Networks can be split into three
types by geographical coverage Local Area Network LAN Metropolitan
Area Network MAN Wide Area Network WAN 18
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Local Area Network - LAN Single campus Can be multiple networks
interconnected No special telecommunications hardware is necessary,
as cables/signals never leave the companys premises Fast data
transfer rates reliability of transmission not always top priority
damaged data can be re-transmitted easily Video-conferencing is
feasible 19
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Metropolitan Area Network - MAN Multiple campuses e.g. within a
city small geographical area Australians use MANs to interconnect
South Eastern cities Slower data transfer rates? need reliability
of WANs with speed of LANs 20
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Wide Area Network - WAN The rest of the planet Slower data
transfer rates (end to end) reliability is a high priority
retransmission of missing data is a large overhead extensive use of
external telecommunication systems backbone transfer rate is now
faster than LANs! The Internet International telecommunications
Satellite systems e.g. Global Positioning System - GPS 21
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Janet backbone All UK academic institutions access the internet
via the Janet network.ac.uk domain Funded by Joint Information
Systems Committee (JISC) In October 2006 SuperJANET5 was launched
after 29 million of investment. It provides a 10Gbit/s backbone,
with an upgrade path to 40GBit/s over the next few years. Most
organisations connected by twenty WANs 22 Map from
http://www.janet.ac.uk/about/topology/SJ5-topology-map.pdf
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Intranets Private network contained within an enterprise May be
a combined topology network leased lines for a WAN gateways to
external internet Uses Internet protocols TCP/IP HTTP, FTP, DNS,
etc Typically, an intranet is contained within security firewalls
it can be thought of as a private internet 24
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Intranet Features Uses private network features Personal
Information Manager using Lotus Notes, Microsoft Outlook Uses
Internet features email web-page browsing standard browsers Uses
dedicated (not shared lines) 25
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Extranets Uses Internet protocols and the PSTN (public switched
telephone network) securely shares enterprises information or
operations part of companys intranet extended to external users
Security achieved with firewalls digital certificates issued by an
agency, establishes credentials on-line Used by Tele-workers at
home, consultants, partners, customers other companies suppliers,
vendors, etc. 26
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Extranet Usage Exchange large volumes of data Electronic Data
Interchange (EDI) Collaborate with other companies or customers
Jointly develop and use training programs Provide or access
services provided by one company to a group of other companies
online banking application managed by one company on behalf of
affiliated banks Share news of common interest 27
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The Internet International computer network connecting
government agencies, universities, research institutions,
businesses, and individuals Started as a US Defence Department
network to distribute US military computing capability resist
(nuclear) attacks / natural disasters Evolved into a network used
by academics, scientists, governments and, now, everybody! the US
government ceased to administer it in 1992 became civilian 28
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Summary Introduction to networks what is a network, why? basic
types of networks Geographical descriptions LAN, MAN, WAN
Intranets, extranets and the Internet definitions 29