Web Programming– UFCFB3-30-1 Lecture 2 Instructor : Mazhar H Malik Email : mazhar@gcet.edu.om Global College of Engineering and Technology

Previous Lecture The World Wide Web environment. Describe the history and development of the WWW. WWW vs Internet vs Networking. Describe WWW contents. 6/12/2018 Lecture 2

Today’s Lecture LAN and WAN, TCP and UDP Packet vs Circuit Switching Protocols Internet Protocol Suit Web forms Scripts and Applets FTP 6/12/2018 Lecture 2

Lecture 2 - The Internet as a Network LO 1 6/12/2018 Lecture 2

Networks Advantages: Disadvantages: Enable people to work together Reduce costs from sharing networked hardware and software Increase productivity by sharing data Provide access to a wide range of services and specialized peripheral devices Disadvantages: Unavailable resources when network malfunctions More vulnerable to unauthorized access than stand alone computers Susceptible to an increased number of worms, Trojan horses, and blended threats

Local Area Network (LAN) Network of computers located in a single location, like a home, school, or office building Can share connection with other LANS and with the internet

Characteristics of a LAN? Local area network Relatively limited in size Computers connected in small areas Same office True peer-to-peer Can support limited number of nodes

Wide Area Network (WAN) Network over a large area like a city, a country, or multiple countries Connects multiple LANs together Generally utilizes different and much more expensive networking equipment than LANs The internet is the most popular WAN

Suggested reading - Chapter 2, Discovering Computers 2007 Key words Node Any device connected to a network Your computer at home, one in the lab, one out there on the internet Has a unique network address Client Any node that requests and uses resources available from other nodes. Usually from another computer, often a computer called a server Server A node that shares resources with other nodes File server, print server, mail server or web server Client-server relationship Can be file server, printer server, communications server, Web server, Database server depending on the resources being shared. Suggested reading - Chapter 2, Discovering Computers 2007 6/12/2018 Lecture 2

TCP and UDP TCP or Transmission Control Protocol and UDP or User Datagram Protocol. TCP is connection oriented – once a connection is established, data can be sent bidirectional. UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP. 6/12/2018 Lecture 2

e.g User Name and Password e.g Audio, Video and Gaming Traffic TCP UDP Connection Oriented Connection Less Reliable Not Reliable Slow Fast e.g User Name and Password e.g Audio, Video and Gaming Traffic 6/12/2018 Lecture 2

Packet switched network Packets (units of information) are routed between nodes over data links shared with other traffic Contrasts with circuit switching, which sets up a dedicated connection between the two nodes for their exclusive use for the duration of the communication Packet switching… Makes best use of the capacity in a network Improves time it takes for data to pass across the network Increases the stability of the network 6/12/2018 Lecture 2

Packet switching Files to be transmitted are divided into packets Labelled with to, from, and # of # Sent across the network…may take different routes Put together at the destination Missing packets are re-sent 6/12/2018 Lecture 2

Circuit and Packet Switching (1) circuit switching (example: telephone networks) • a sequence of links (communication path) between two communicating nodes is determined ahead of the actual communication • data is sent as a stream of bits through the network. packet switching (example: the Internet) data is sent through network in short blocks – packets network links are dynamically shared by many packets; each packet uses full link bandwidth 6/12/2018 Lecture 2

Circuit switching Steps (1) circuit establishment • before any data is transmitted, an end-to-end circuit must be established, i.e. network resources on path/ links between end-devices must be reserved (2) data transfer • data transmission and signaling may each be digital or analog . (3) circuit disconnect • after some period of data transfer, the connection is terminated, by action of one of two stations, and dedicated resources are released. 6/12/2018 Lecture 2

Protocols The standards that specify how the network functions The set of rules for communication over the network The language or the grammar that allows computers to “talk” to each other The Internet uses many protocols 6/12/2018 Lecture 2

Internet protocol suite Designed to be independent of the underlying physical medium Any communications network, wired or wireless, that can carry two-way digital data can carry Internet traffic Thus, Internet packets flow through wired networks like copper wire, coaxial cable, and fibre optic, and through wireless networks like Wi-Fi. Together, all these networks, sharing the same protocols, form the Internet 6/12/2018 Lecture 2

TCP/IP IP - Internet Protocol TCP - Transmission Control Protocol Handles the packets TCP - Transmission Control Protocol Handles the sending (routing) of the packets from sender to receiver via nodes on the network 6/12/2018 Lecture 2

Internet addresses IP address Unique to each device connected 4 groups of numbers, each separated by a full-stop. Each of the four numbers is 0 - 255 A word equivalent (URL - uniform resource locator) is easier to remember 216.239.39.99 = www.google.com 6/12/2018 Lecture 2

Connectivity This can be a hard word to define in computer science terms Generally it means the ease and ability of devices to connect and share digital data Includes computers, phones, PDA’s, etc, wired and wireless Refer to the picture on the title slide 6/12/2018 Lecture 2

Email Create, send, receive, forward, store, print and delete electronic messages Can attach files e.g. graphic, video, Word document or spreadsheet 6/12/2018 Lecture 2

6/12/2018 Lecture 2

Forms on web pages Web page users often fill in a form, e.g. Feedback eCommerce - a shopping cart is an extended form Subscribe, enrol at university etc Design is important Easy and clear to use People will use it People will use it correctly and give the information you want Conforms to technical standards Will display and function reliably 6/12/2018 Lecture 2

Submit button. Needs a reset button too Parts of a web form A drop-down list Radio buttons; can only select one Check boxes; can select more than one Text box - usually a set size Note that this example form is not very well designed! Submit button. Needs a reset button too Text box displays * instead of text; usually for passwords Text box; large field 6/12/2018 Lecture 2

How a form is processed User completes the form and clicks Submit (or Send? or Finished? or OK? What is the best word?) A script* or applet* runs Transmits the data to the server, and if needed, sends data back to the client e.g. “Thank you, your order is being processed” Usually the data goes to a database, or is emailed * See next slide 6/12/2018 Lecture 2

Scripts and Applets A script or an applet is a mini computer program that runs on the client’s computer It is usually downloaded with the web page, in the background. When needed (e.g. by clicking on “Submit”) it runs An applet usually runs faster than a script Scripts and applets communicate with the web server using the common gateway interface (CGI) communication standard 6/12/2018 Lecture 2

FTP File Transfer Protocol Used to transfer data from one computer to another over the Internet, or through a network Example - create a website on your machine; use FTP to copy the site to the web server; now everyone can use the site Then use FTP to update the files as you maintain the site 6/12/2018 Lecture 2

Revision and Questions? 6/12/2018 Lecture 2