COMP2221 Networks in Organisations

1. COMP2221Networks in Organisations Richard Henson February 2012

2. Week 1: Standards and Computer Networks • Objectives • Explain evolution of data transmission through networks • Define standards • Explain how standards work and why they are so important for digital networks

3. History of Electricity-basedCommunication Networks • Used for centuries before organisations used Computers… • Chronologically: • Telegraph (1840s) • Telephone (1910s) • Telex (1930s) • Internet/first digital WANs (1970s)

4. Each network developed its own standards for… • Creation of data • Format of transmitted data • Voltage • Error-checking • Receiving, storing, presentation of transmitted data

5. National and International Networks • Telegraph :transmitted data within a particular country • developed National standards • e.g. in the UK… BS standard • Telephone: • initially National standards • developed International calling • French-based standards became the Internationally recognised ones (CCITT) • ComitéConsultatifInternational Téléphonique et Télégraphique

6. A tale of standards… • Roman Empire, AD 0 • urban streets were open sewers • Created Passing places created • stone paths across the street • Needed to leave spaces for chariot wheels • how wide?

7. What width to choose? • Standard “wheelbase” width agreed (4’ 8½’’) • Used for chariots throughout Roman Empire • Revived in UK as “standard gauge” for railway tracks (1830s) • most railways around the world still use the 4’ 8½ standard to this day • even Space Shuttle was transported on 4’ 8½’’ tracks (!)

8. Breaking a standard? • Why stick to standard gauge? • everyone else uses it! • Most powerful railway company in the UK (GWR: The Great Western Railway) tried to change the standard width of a track to 6’ 0’’ • used the 6’ “Broad Gauge” for all their tracks • wider carriages, more passenger comfort… • Other railways maintained 4’ 8½’’ !!! • GWR eventually gave up and converted all their tracks to the standard gauge

9. Lessons from this story • Large, powerful organisations try to make their own standards universal • Existing standards are difficult to change • Once established, standards may well be adopted world-wide • Standards therefore need to be right!

10. CCITT and Computer Standards • In the early days, CCITT laid down the standard… (like the Romans…) • More recently, CCITT became ITU: • International Telecommunication Union • Through ITU, many CCITT standards applied to computer networks: • Group 3: protocol for sending fax documents across (analogue) telephone lines • Group 4: protocol for sending fax documents over ISDN networks (more on these later) • “V” modem standards

11. Comparison of Computer & Telecoms Networks • Information sent is digital (!) • all prior CCITT etc. standards were analogue… • potential range of uses of devices are much more flexible • Control doesn’t have to be centralised • fundamental difference with CCITT-standardised networks

12. Standards in Computing • Area of rapid change • Early emerging standard… • may be eclipsed by new technology • Standards usually follow many years after the products themselves have been on the market • Means they are often based on specific products (usually the market leader at the time!)

13. Standards • Definition: • “A standard is an established or accepted model” • Communication protocols… • “Elements of a communication system that are defined by an agreed set of rules, conditions, parameters or methods”

14. Type of Standards • De Facto • A product or service that is a standard by virtue of its widespread use by interested users • De Jure • The standard devised by a committee of the organisation or, a working group of a subcommittee of a committee of the organisation

15. Standards and IT Professionals • Standards: • ensure that products can communicate • identify incompatibilities between products • provide a check that customers are buying the correct product • ensure that customers are not buying a manufacturer dependent product

16. ISO (International Standards Organisation) • Been providing International standards for many areas • Even for management systems: • ISO9001 • ISO14001 • ISO27001

17. ISO Development Process (1) • ISO standards panel convened: experts in the relevant field • decide the contents of the definition of draft standard • proposal passed to the parent committee for ratification before publication as, first, a draft for discussion (DD)

18. ISO Development Process (2) • Once ratified, it becomes a draft international standard • Once the document has been available for a certain amount of time… • allowing full scrutiny… • it becomes a full International Standard (an ISO)

19. Proprietary Systems • Big computer manufacturers in the 1960s and 1970s worked independently to produce their own software • Teams of researchers to develop their own systems for communicating between devices • Different research teams, differentcompany aims, so products incompatible

20. Proprietary Systems • Considered to be a good thing by companies such as IBM and ICL, because it “locked” customers into their products • Not popular with customers, who wanted to be able to buy more freely • Also a barrier to communication: • between companies • sometimes between different parts of the same company • Because they were using incompatible systems

21. Open Systems • ISO aware that the basic infrastructure for global digital communications was rapidly emerging in the form of the Internet • ISOdecided that the existing proprietary isolationist stance was not condusive to the growth of effective digital data communications on a world-wide basis • ISO agreed that what was needed was open systems

22. Open Systems • Definition: • “a computer system that is ‘open’ for the purpose of information exchange” • Open systems are therefore not restricted to one particular manufacturers own system of communicating • Open systems should provide the ability to: • interchange applications and data • between systems with different underlying hardware and software

23. Open Systems Interconnect (?) • Historic meetings in Geneva co-ordinated by ISO (back in 1977, 1978) • Involved proprietary systems manufacturers, telecomms companies and researchers • Agreedto produce a software model for open systems • accepted that this would take years to achieve • the industry could, however, at least aspire to this in new developments… • Model became known as the Open Systems Interconnection model (OSI model)

24. LANs, WANs, Standards • The PC changed everything… • When it became possible to network PCs, new sets of protocols and technologies were developed & used • new classification required: • LAN: generally applied to PC/Unix networks within institutions (IEEE) • WAN: existing networks that covered longer distances (CCITT??? ISO???)

25. OSI Model & WAN standards • OSI soon caught on • challenge to CCITT • teamed up with IEEE (802 standards) • In 1984, OSI became an International Standard (!) • open systems had credibility!!! • Proprietary systems had competition…

26. Why link PCs together to make LANs (revision) • Workshop in small groups • Each group - four reasons • Ten minutes

27. What makes up a LAN (1)? • Hardware: • computers and other network devices • e.g. printers, web cameras • transmission media, e.g. cable, radio waves • network cards, which link the network devices to the transmission media

28. What makes up a LAN (2)? • Software to (just a sample…) • send/receive data • provide an even flow of data between devices • make sure sent data goes to the right place • provide a path for data through the network • make sure data is checked for corruption as it passes through the network • anything else that may need to be done to the data e.g. formatting, compression, encryption

29. Some reasons to keep PCs “standalone” • Workshops again… • Another four reasons • Ten minutes

30. Transfer of data through LANs • Cables designed to transmit high volumes of digital data • Network cards provide the computer-medium interface: • control flow rate and error checking of data • send/receive data at high, and even higher… speeds

31. LAN connections • Computers physically connected using: • cabling (or e/m radiation of an appropriate frequency) • network cards • networking software • If a cabled LAN connection exceeds: • 100 metres (twisted pair cabling) • 185 metres (coaxial cabling) • then a repeater (booster) is needed

32. More about LANs • The network card fits inside the computer: • either as a separate card • or on the motherboard… • uses own software • works with other software that bind together to control the sending and receiving of data • If the network is of the client-server type, more complex server software is needed at the “server” end • If a peer-peer network, connectivity software is less sophisticated…

33. More about LANs • Other hardware names: • Nodes: are computers and other intelligent devices with MAC and IP addresses • Repeaters: boost weak digital signals • Hubs: link devices & direct data round a cabling system more efficiently • most hubs are also repeaters • Switches: powerful routers that can process and filter the data in various ways way, whilst hubs just send it on

34. Classification of Networks by management • Client-Server Networks • networked computers either clients or servers • Peer-Peer Networks • networked computers all of equal status

35. Client-Server Networks • A client requests services from a server • Client-server interprocess communication (IPC) fast and reliable • Types of clients: • computer workstation (“fat” client) • computer with limited local storage and processing (“thin” client) • printer with processing ability

36. Workstations • Like a standalone computer in many respects. • Differences: • additional hardware • e.g. network card • include the basic networking software required: • to allow connection to the network • to communicate effectively with other network nodes • All computers in a peer-peer network are workstations

37. Servers • High-powered computers • high storage capacity • a lot of memory • Provides network services which are access by users through clients • requires a highly specialized software called a Network Operating System (NOS) • Examples Network Operating Systems: • Windows NT/2000/XP/2003/Vista • Netware • UNIX e.g. Linux

38. Servers in small networks • Scenario: a single server is the central controlling point • The server also looks after security on the network: • only allows valid users to log on • only allows access to resources for users that have logged on • stores appropriate “user rights” for access to its files and directories

39. Servers in small networks • This same server offers all the normal network services: • Applications • when a user wants to use an application on the server, it accesses the software from the server • Printing • the user selects a printer via the server • File Access • users with permission directly access files on the server

40. Problems with this Scenario? • Discussion in Groups… Possible Solutions? • Further Discussion…

41. Servers in Larger Networks • Larger networks have MANY servers (the University ITS network currently has at least 50) • functions can be distributed around different individual servers. Examples: • Login Server • File and Print server • Applications Server • Internet Gateway

42. Login Servers (the most crucial!) • Dedicated to logging on users • database of usernames/passwords • Only allows a potential user to access the network if both username and password exactly correspond with entries in the database • In Windows networks known as Domain Controllers

43. Peer-Peer networks • Also known as workgroups • No central server • Computer nodes can act as both clients and servers • No expensive powerful machine dedicated to providing services

44. Peer-Peer networks • No servers! • All users have the following responsibilities: • security & network administration • provide access to their computer’s services and resources

45. Advantages & disadvantages of Client-Server, compared to Peer-peer • In groups… • Don’t look at next slides!

46. Advantages of a client-server network, compared to a workgroup • Centralised security • Centralised access to resources • Centralised network administration • With more than about 10 users, much easier to manage than a workgroup. Can handle up to thousands of users

47. Disadvantages of client-server, compared to a workgroup • Expensive dedicated computer not accessible to users • Expensive server operating system needed • Network management required • Reduces user autonomy • If the server goes down, the network ceases to function

48. Thanks for listening 