COMP2221 Networks in Organisations Richard Henson February 2012

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

History of Electricity-based Communication Networks n Used for centuries before organisations used Computers… n Chronologically: –Telegraph (1840s) –Telephone (1910s) –Telex (1930s) –Internet/first digital WANs (1970s)

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

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

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

What width to choose? n Standard “wheelbase” width agreed (4’ 8½’’) n Used for chariots throughout Roman Empire n 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 (!)

Breaking a standard? n Why stick to standard gauge? –everyone else uses it! n 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… n Other railways maintained 4’ 8½’’ !!! n GWR eventually gave up and converted all their tracks to the standard gauge

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

CCITT and Computer Standards n In the early days, CCITT laid down the standard… (like the Romans…) n More recently, CCITT became ITU: –International Telecommunication Union n 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

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

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

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

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

Standards and IT Professionals n 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

ISO (International Standards Organisation) n n Been providing International standards for many areas n n Even for management systems: – –ISO9001 – –ISO14001 – –ISO27001

ISO Development Process (1) n ISO standards panel convened: experts in the relevant field 1.decide the contents of the definition of draft standard 2.proposal passed to the parent committee for ratification before publication as, first, a draft for discussion (DD)

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

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

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

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

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

Open Systems Interconnect (?) n Historic meetings in Geneva co-ordinated by ISO (back in 1977, 1978) n Involved proprietary systems manufacturers, telecomms companies and researchers n Agreed to 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… n Model became known as the Open Systems Interconnection model (OSI model)

LANs, WANs, Standards n The PC changed everything… n 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???)

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

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

What makes up a LAN (1)? n 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

What makes up a LAN (2)? n 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

Some reasons to keep PCs “standalone” n Workshops again… n Another four reasons n Ten minutes

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

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

More about LANs n 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 n If the network is of the client-server type, more complex server software is needed at the “server” end n If a peer-peer network, connectivity software is less sophisticated…

More about LANs n 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

Classification of Networks by management n Client-Server Networks –networked computers either clients or servers n Peer-Peer Networks –networked computers all of equal status

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

Workstations n Like a standalone computer in many respects. n 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 n All computers in a peer-peer network are workstations

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

Servers in small networks n Scenario: a single server is the central controlling point n 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

Servers in small networks n 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

Problems with this Scenario? n Discussion in Groups… Possible Solutions? n Further Discussion…

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

Login Servers (the most crucial!) n Dedicated to logging on users –database of usernames/passwords n 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

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

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

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

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

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

Thanks for listening Thanks for listening