44212: Web-site Development

1. 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/

2. 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.

3. 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 mustbe transmitted.

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

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

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

7. 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.

8. Internet = Client/Server Network • Client/Server? • 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.

9. 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.

10. 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.

11. 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

12. 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

13. 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.

14. 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.

15. 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.

16. 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/

17. 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.