Introduction to Web Technologies Introduction to the Internet and TCP/IP 21 th January 2005 Dr Bogdan L. Vrusias

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Open Systems Systems whose architecture is not a secret (open source) Operating Systems (Unix, Linux) Programming Languages (Java) Web Servers Protocols (TCP/IP, HTTP) Databases The Internet supports the idea of Open Systems

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Topology Bus network –Simple –Based on component id Ring network –Central unit carries out the process of sending and forwarding messages in the network. Hub network (most popular) –Backplane cable –Ports

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Bus network

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Ring network

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Hub network

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Layered Models Network protocols are partitioned into layers corresponding to the type and level of functionality that each layer carries out. Layers in the OSI (Open System Interconnection) model: –Application: where applications reside –Presentation: acts as a buffer between the application layer and the remaining layers –Session: synchronises the exchange of data between applications –Transport: responsible for the transfer of data through a network –Network: carries out the physical routing of data from one computer to another –Data Link: carries out the process of managing the transmission of low- level items of data such as bytes –Physical: responsible for the low-level process of sending the electrical signals

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © What the Web is Web is the network of computers that contain information that one can view from a browser. The Internet is not a network of computers but, rather, it is a network which consists of a number of other sub- networks The internet consists of computers that communicate through an Internet Service Provider (ISP). The intranet is a private network that allows access only to computers directly connected to it. An extranet extends the intranet by allowing specific customers to access parts of the intranet.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © What the Web is The World Wide Web (WWW) is the collection of interlinked documents (also called Web pages) over the Internet. The Web pages can be viewed through a Web browser (such as Microsoft Internet Explorer, Netscape, Mozilla, Opera, etc.) The Web pages are located on a Web server, from which a Web browser downloads the page to the client and displays it. The collection of Web pages is called a Web site.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © History: The Internet 1960… beginning of the Net The Advanced Research Projects Agency (ARPA) of the Department of Defence implemented the ARPAnet (grandparent of today's Internet). Multiple users where able to send and receive information over a common communication path simultaneously. Internet and Intranet evolved very fast and ARPA created the TCP/IP as a combined set of protocols for communication.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © History: WWW The information carrying capacity (bandwidth) and the popularity has increased tremendously over the years, and lots of businesses rapidly realised the benefits of the Internet. 1990… Tim Berners-Lee of CERN (the European Laboratory of Particle Physics) developed the World Wide Web (WWW). WWW allowed businesses and everyday users to browse or even create multimedia-based documents over the Web. FUTURE: The GRID?

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Internet Structure Popular Internet protocols: –Telnet –FTP (File Transfer Protocol) –SMTP (Simple Mail Transfer Protocol) –Kerberos –DNS (Domain Name System) –TCP (Transmission Control Protocol) –UDP (User Datagram Protocol) –IP (Internet Protocol.)

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Internet Structure

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Ports Given a destination computer address, data is transferred via a protocol suite such as TCP/IP over a network. A port is a conduit into a computer through which data flows. A port on a computer is identified by a unique number –0 to 1023 are reserved for special services –1024 and above can be used for any user application

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Ports

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Internet Addresses How does a computer specify a possible destination computer? The IP address is the dotted quad notation –E.g

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Domain Names Top-level domain nameOrganisation comCommercial company edu or acEducational govGovernmental milMilitary bizShow business orgOrganisations not catered for above aeroAeronautics

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Internet domain name system

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Name Servers A Name Server is a computer that contains Internet addresses and provides the service of translating a symbolic name into some address. The collection of name servers is known as the Internet Domain Name System or DNS. One of the most used part of the Internet! Every time someone sends or consults a Web document then the service is consulted.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Network Concepts: Clients and Servers A server is a computer on a network which carries out some service for another computer known as a client. –E.g. A computer with a browser (client) requesting a Web page from another computer that holds Web pages (server or specifically Web server).

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Clients and Servers A server is a computer which carries out a service such as printing out a file or responding to a web page. –A file server provides files for the clients that ask for its service. –Database servers are computers which store large collections of data which are structured. –Groupware is software which organises the work of a number of staff in some enterprise. –A web server is a typical type of file server that contain files which store the various components of a web site. –A mail server is a computer which has the task of receiving, storing, and sending e- mail. –Object servers are design to hold distributed objects and provides facilities for programs executing on a client computer. –A print server is a computer which receives requests from clients for printing. –An application server is a server which is dedicated to one or more particular applications and contains special-purpose programming code that is specific to that application. A client is some computer which requires a service.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Web Server A Web server is a server which dispenses documents that reside on the World Wide Web.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Protocols A language which embodies the functions required by an entity in a distributed system (usually a client) which another entity provides (usually a server)

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © How the Web Works The user requests to view a Web page from the Web Server by opening a Transport Control Protocol (TCP). Each Web page has a Uniform Resource Identifier (URI), which is a uniform naming scheme for all the resources on the Internet (or Intranet). There are two types of URIs the Uniform Resource Locator (URL) and the Uniform Resource Name (URN). –URL: –URN: urn:def://JavaScript Each Web server has a unique Internet Protocol (IP) address (e.g. University of Surrey has ). The URI is translated into the corresponding IP address through the Domain Name System (DNS).

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © How the Web Works The user communicates with the server through the HyperText Transport Protocol (HTTP), the network protocol for the Web. The server then processes the client's request and sends the response to the client's browser The browser then parses the HTML it receives, and then it displays it's content. 6. Browser processes HTML and displays page. 2. Client requests a web page 1. Author writes instructions 3. Web server locates instructions file 4. Web server processes instructions to create HTML 5. HTML stream returned to browser

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Tiered Architectures A tier is a logically separated and encapsulated set of processes. two-tier –presentation and logic layer and a database layer three-tier –presentation layer, processing layer (or application server layer) and data layer n-tier

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Middle Tier The middle layer enables the developer to isolate the main part of an application that can change over time. In this layer can be found objects known as business objects.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Three-Tier Architecture

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Class Exercise Consider the following scenarios: –A) A Web application for displaying pages (containing any subject), comprising lots of information, and presentation is important. –B) A Web application that allows users to buy books online. What architecture would you choose for developing each Web application, how many tiers? How would you distribute the processing in each tier? Consider the cases where the website is expected to receive lots of hits constantly and the case where the website is expected not to get busy.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Advantages of Three-Tier Architectures It isolates the database technology used to implement the final layer. It removes a large amount of code from the clients and places it on the server. It fits in with modern object-oriented ideas as the processing code is associated with objects.

Introduction to Web Technologies 21 th January 2005Bogdan L. Vrusias © Closing Questions??? Remarks??? Comments!!! Evaluation!