Introduction to Networks: Types, Purpose, and Structure in Computer Science

1. phones off(please) CSCI1412Lecture 15 Networks 1 Introduction to Networks Dr John Cowell

2. Overview • Introduction to networks • what is a network, why? • basic types of networks • Geographical descriptions • LAN, MAN, WAN • Intranets, extranets and the Internet • definitions

3. Introduction

4. 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

5. Why use a Network? • Improve communications • team working • Share resources • hardware • software • data • Central services • Efficiency

6. 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

7. Peer to Peer • Simplest is peer-to-peer, connected via serial/parallel ports • RS 232 • null modem cable

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Three Tier Model • The three parts are business logic Controls interaction between a Database and a user interface data services database engine user services front end application

16. 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

17. Geographical Descriptions

18. 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

19. Local Area Network - LAN • Single campus • Can be multiple networks interconnected • No special telecommunications hardware is necessary, as cables/signals never leave the company’s premises • Fast data transfer rates • reliability of transmission not always top priority • damaged data can be re-transmitted easily • Video-conferencing is feasible

20. 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

21. 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

22. Janet backbone • All UK academic institutions access the internet via the Janet network • .ac.ukdomain • 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 Map from http://www.janet.ac.uk/about/topology/SJ5-topology-map.pdf

23. Intra, Extra and Internet

24. 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

25. 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)

26. Extranets • Uses Internet protocols and the PSTN (public switched telephone network) • securely shares enterprises’ information or operations • part of company’s 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.

27. 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

28. 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

29. Summary • Introduction to networks • what is a network, why? • basic types of networks • Geographical descriptions • LAN, MAN, WAN • Intranets, extranets and the Internet • definitions