CSCI1412 - Introduction to Networks

CSCI1412Lecture 15Networks 1Introduction to NetworksDr John Cowell

phones off (please)1OverviewIntroduction to networkswhat is a network, why?basic types of networksGeographical descriptionsLAN, MAN, WANIntranets, extranets and the Internetdefinitions2Introduction3What is a Network?A network is a communication systema collection ofresourceshardware & softwareobjectspeopleVarying types of networkcomputertelephonesAny two or more interconnected computer systems can be described as a network4Why use a Network?Improve communicationsteam workingShare resourceshardwaresoftwaredataCentral servicesEfficiency5Types of NetworksThere are several different types of networksDepends onconnectivitygeographic area coveredtopology/protocolConnectivitypeer to peerclient / serverdistributed systemthree tier architecture6Peer to PeerSimplest is peer-to-peer, connected via serial/parallel portsRS 232null modem cable

7Windows Peer-to-PeerWindows allows creation of larger peer-to-peer networks, using network protocolsresources, e.g. printers, modems, attached to one PC, but can be shared by other usersUse Control Panel/Networks to configure

8Client / ServerAs number of users / workstations increases, it is more efficient to create a client / server networkMultiple workstations connected to one or more network serversfile serverprint servercommunications serverfax server9Client / Server CommunicationClients and servers can also be viewed as being software applicationsInteract by using one of several methodsmessage passingremote procedure callsSynchronicity is importanti.e. server cannot process until client has sent request client passes values to server, then waitsserver processes values, returns resultsasynchronous relationshipServers may have higher network priorityaccess to otherwise restricted system resources10Servers 1File servershared data can be stored and managed centrallyaccess can be controlled/loggedPrint servermultiple printers can be connected to serverserver organises print queuesNetwork printersdirect connection to network11Servers 2Communications serveracts as interface between network and outside worldother networksthe InternetFax serverfaxes are a different technology to email, etcserver handles user requests to send faxes12Distributed SystemsPhysically separate computers in a network operate together as a single logical unitBeowulf clustersAppears to a user to be a single computerphysically separatedan operating system that supports distributed systems is required, e.g. UNIXadvantages includereduction in costs and delays in transmitting and processing datareduced load on the host processorbetter local control and service13Three Tier ArchitectureClient / server model has some problemsnot scaleablebusiness rules not deployed centrallyconsumes too many resources on client machineinefficientOne proposed solution is to partition applications into logical partseach part can have multiple units14Three Tier ModelThe three parts are

15user servicesfront end applicationdata servicesdatabase enginebusiness logicControls interaction between a Database and a user interfaceThree Tier BenefitsFour major benefits (are claimed)reusecomponents are shared between applicationstime in design and implementation not wastedmaintenanceas business changes, modifications in applications and business rules are easier to implementperformanceoptimised as individual components can be upgradedmanageabilitycomplex application is broken down into smaller componentseasier to work with16Geographical Descriptions17Geographical Network AreasNetworks can be split into three types by geographical coverageLocal Area NetworkLANMetropolitan Area NetworkMANWide Area NetworkWAN18Local Area Network - LANSingle campusCan be multiple networks interconnectedNo special telecommunications hardware is necessary, as cables/signals never leave the companys premisesFast data transfer ratesreliability of transmission not always top prioritydamaged data can be re-transmitted easilyVideo-conferencing is feasible19Metropolitan Area Network - MANMultiple campusese.g. within a citysmall geographical areaAustralians use MANs to interconnect South Eastern citiesSlower data transfer rates?need reliability of WANs with speed of LANs20Wide Area Network - WANThe rest of the planetSlower data transfer rates (end to end)reliability is a high priorityretransmission of missing data is a large overheadextensive use of external telecommunication systemsbackbone transfer rate is now faster than LANs!The InternetInternational telecommunicationsSatellite systemse.g. Global Positioning System - GPS21Janet backboneAll 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

22Map from http://www.janet.ac.uk/about/topology/SJ5-topology-map.pdfIntra, Extra and Internet23IntranetsPrivate network contained within an enterpriseMay be a combined topology networkleased lines for a WANgateways to external internetUses Internet protocolsTCP/IPHTTP, FTP, DNS, etcTypically, an intranet is contained within security firewallsit can be thought of as a private internet24Intranet FeaturesUses private network featuresPersonal Information Managerusing Lotus Notes, Microsoft OutlookUses Internet featuresemailweb-page browsingstandard browsersUses dedicated (not shared lines)25ExtranetsUses Internet protocols and the PSTN (public switched telephone network)securely shares enterprises information or operationspart of companys intranet extended to external usersSecurity achieved with firewallsdigital certificatesissued by an agency, establishes credentials on-lineUsed byTele-workers at home, consultants, partners, customersother companiessuppliers, vendors, etc.26Extranet UsageExchange large volumes of dataElectronic Data Interchange (EDI) Collaborate with other companies or customersJointly develop and use training programs Provide or access services provided by one company to a group of other companiesonline banking application managed by one company on behalf of affiliated banks Share news of common interest27The InternetInternational computer network connecting government agencies, universities, research institutions, businesses, and individualsStarted as a US Defence Department networkto distribute US military computing capabilityresist (nuclear) attacks / natural disastersEvolved into a network used by academics, scientists, governments and, now, everybody!the US government ceased to administer it in 1992became civilian28SummaryIntroduction to networkswhat is a network, why?basic types of networksGeographical descriptionsLAN, MAN, WANIntranets, extranets and the Internetdefinitions29