44212: Web-site Development How the Internet/Web Works Ian Perry Room: C49 Extension: 7287 E-mail: I.P.Perry@hull.ac.uk http://itsy.co.uk/ac/0506/Sem1&2/44212_WSD/

How does the Internet work? Just like any other Network! Hardware provides physical structure: cables (copper & fibre), hubs, switches, routers, servers, satellites, plus the client computers themselves. Software facilitates the exchange of data (communication) over physical network: Software that enables networking follows a set of rules; a protocol.

What are Protocols? Rules for communication to understand & act on messages sent/received, computers at both ends of the ‘conversation’ must agree on what a message means. Description for each type of activity e.g. establishing a remote connection, exchanging e-mail, or transferring files, requires agreed definition of: the format that messages must take. how messages must be transmitted.

‘Snail-mail’ Protocols The ‘Rules’ that govern how we address letters, and how the Post Office handles those letters: Mail Box Post Office The rules (protocols) of the Postal System ensure that a properly addressed letter (format) will reach its destination via a delivery route (transmission). Train/Van Destination Post Office

Protocols = Interoperability For the Internet to be really useful: different types of computers, using different operating systems, must be able to connect, & communicate with each other. they can, as long as they conform to Internet Protocols.

The Internet Protocol TCP/IP a suite, or family, of protocols; Transmission Control Program / Internet Protocol a suite, or family, of protocols; enabling messages to be correctly formatted and transmitted from computer to computer irrespective of computer type/operating system. How many of you can speak Esperanto? TCP/IP = Esperanto for Computers

Other Internet Protocols File Transfer Protocol (FTP) to transfer files between computers. Simple Mail Transfer Protocol (SMTP) to send e-mail. Post Office Protocol (POP3) for retrieval & management of e-mail. HyperText Transfer Protocol (HTTP) to transmit Web-pages over the Internet.

Internet = Client/Server Network a networking model consisting of a series of requests and responses. Client Programs make requests & format responses Server Programs ‘answer’ requests & provide responses Very efficient in sharing a limited resource (i.e. Bandwidth) with many users: connections only formed ‘as-and-when’ required.

Client/Server Transactions File Transfer (via FTP) Client program contacts an FTP Server and requests transfer of a file; FTP Server responds by transferring the file to the Client’s computer. E-mail (via SMTP & POP3) Client program allows user to interact with an e-mail Server to send (SMTP) and receive (POP3) electronic mail messages. Web (via HTTP) Client program request the contents of an HTML page from a Web Server; and displays the result, as a Web-page, on the Client computer.

Internet Addressing People/Computers communicating via the Internet need to know where they are located, i.e. their ‘address’. The term “address” is used somewhat loosely on the Internet, and might refer to: a ‘computer network’, a ‘computer’, a ‘software application’, a ‘file’, etc. 1

IP Address = ‘Real Address’ All ‘intelligent devices’ on the Internet (i.e. every computer, router, switch, etc.) must have a unique IP Address. An IP address consists of four numbers, between 0 and 255, separated by dots. Sometimes called a ‘dotted quad’. e.g. 150.237.176.24 3

Domain Name = ‘Human-friendly’ Domain Name Servers maintain a distributed database; the Domain Name System (DNS) Match ‘human-friendly’ Domain Names to ‘real’ IP addresses. e.g. the Domain Name: www.hull.ac.uk is a lot easier to remember than: 150.237.176.24 4

Internet Domains The Internet’s domain name system ‘describes’ a hierarchy of domains. Top-Level-Domains (sector/country) .com, .edu, .co.uk, ac.uk, etc. Sub-Domains (organisation) ibm, mit, eyms, hull, etc. Servers (service) www, pop, ftp, etc.

E-mail Addresses Email Addresses identify both a person and the sub-domain of the e-mail Server that stores their messages, e.g.: i.p.perry@hull.ac.uk Reading from left to right: i.p.perry = mailbox for this Person/User. hull = who works for this Organisation. ac.uk = which is an Academic Organisation located in the United Kingdom. 5

What is the Web? Basic components are: a Client (i.e. Browser), requesting HTML documents. the Internet, providing a communications channel. a Server (i.e. Web Server), with access to a store of HTML documents.

Web Addresses Relies upon Uniform Resource Locators (URLs) protocol://server.sub-domain.top-level-domain/directory/filename Example URL: http://www.hull.ac.uk/home/index.html Often a URL does not need to include directory/filename: http://itsy.co.uk/ URL might not ‘request’ an HTML document: mailto:i.p.perry@hull.ac.uk ftp://src.doc.ic.ac.uk/ 7

Next Week’s Workshop Next week’s Workshop asks you to locate & analyse the Web-sites of organisations that are ‘similar’ to ABM Car Sales. To see if anything can be learnt (borrowed?) from the experience (mistakes?) of others. You have all read ABM Car Sales Case Study, haven’t you? If not, then make sure you do before next week.