Web Systems Lectures - Week 10 - PDF

Faculty of Information Technology 31268 Web Systems Week 10 The Internet 31268 – Web Systems 1  Web applicatio...

Faculty of Information Technology 31268 Web Systems Week 10 The Internet 31268 – Web Systems 1  Web applications Faculty of Information Technology Web page development – HTML/XHTML – CSS: Cascading Style Sheets Web Infrastructure – Internet Infrastructure – Web servers Web Applications – Online media and file sharing – Communications – Search engines Human Computer Interaction – History of the Internet 31268 – Web Systems 2  The Web … Faculty of Information Technology Is it… A bunch of computers and a network of networks… www.uts.edu.au BROWSER 3  The web… A bunch of computers Faculty of Information Technology and a network of Is It … networks… BROWSER … and a whacking big computer running the web index.html site? www.uts.edu.au 4 Internet Infrastructure Faculty of Information Technology – Typical home network » is a Local Area Network (LAN) ISP Router Ethernet Computer Switch or WiFi 5 Definition of Network Faculty of Information Technology A network is a collection of computers and devices connected together to allow sharing of resources between users. Example 1: Network File System – Part of a remote disk can be made to appear as another hard drive on the local PC. – The physical location of disk storage is transparent to users. Example 2: Printer Sharing – One printer used by several PCs 6 Device Types on the Network Faculty of Information Technology Host: Just another name for computer Modem: Converts between analog signals and digital signals in dialup access NIC (Network Interface Card): Direct connection to local area network Hub Switch Wireless Access Point Router 7  Device: Hub Faculty of Information Technology A hub can connect more than 2 hosts. Strengthens the signal. Not concerned with the meaning of data. Broadcasts the message to all of its ports. Now superseded, limited to ≤ 100Mbps, very hard to find! But useful as tapping devices. 8  Device: Switch Faculty of Information Technology More intelligent than a hub, because a switch looks at the MAC addresses (burned- in physical address of the Network Interface Card) in the messages. Provides a direct physical connection between hosts when they want to communicate. 9 Device: Wireless Access Point Faculty of Information Technology Operates on the 2.4 or 5 GHz bandwidth Several versions - a, b, g, n, ac, … Now ubiquitous 10 Small Network Structure: LAN Faculty of Information Technology A local area network (LAN) is a network that connects computers and devices in a geographically limited area. LAN examples: School computer laboratory. Office buildings ("Campus") 11 Network Topology Faculty of Information Technology Network topology refers to structure of the network. Two types of topologies are: Physical topology (how the data actually is transmitted) Logical topology (only concerned about where the data ends up – the "black box" analogy) Physical network topologies include: Bus, Ring, Star. Logical network topologies include: Bus, Ring 12  Physical Topology: Bus Faculty of Information Technology Physical topology types: Bus, Ring, Bus: allSar the computers or devices directly connect to a common communication medium. 13 Physical Topology: Ring Faculty of Information Technology Ring: all the computers or devices in the network form a closed ring or loop. 14 Physical Topology: Star Faculty of Information Technology –Star: all the computers or devices in a network connect to a central computer or hub. 15 Logical Topology Faculty of Information Technology Logical topology types: Bus, Ring Logical topology dictates how the hosts share access to the network avoiding collisions - the problem of two hosts transmitting data at the same time. Physical topology and logical topology are often different. e.g. A LAN with bus physical topology can have sequential(ring) logical topology. 16 Logical topology: Token Ring Faculty of Information Technology To avoid collision, hosts take turns to transmit data. Permission to transmit is called a token. The token is passed from one host to another according to a set of rules. Often, connected physically in a bus or star topology But computers see this logical topology as a "ring" 17  Logical topology: Bus (ethernet) Faculty of Information Technology All hosts have permission to transmit all the time. When a collision occurs, wait a random amount of time and try again. If a collision occurs again, double the wait and try again. As is typical of Ethernet - the network often has a star physical topology. Reference: http://www.webopedia.com/TERM/C/CSMA_CD.html 18 Internet Infrastructure Faculty of Information Technology – Typical ISP network (called a Wide Area Network (WAN) or Metropolitan Area Network (MAN) ISP 1 ISP 2 Inter-connect Backup Inter- Mix of backbone connect routers, fast switches, servers etc 19 Big Network Structure: WAN/MAN Faculty of Information Technology A wide area network (WAN) is a network that covers a large geographic area. WAN could cover a geographic region like: – A country e.g. Australia – The world eg: the Internet Uses Routers to inter-connect Uses Modems to connect to service provider Uses leased lines, circuit switching, packet switching, wireless, broadband networks 20  Network: WAN connectivity Faculty of Information Technology Typical users: ISP, companies Common tech: – leased lines E.g. HDSL, T1/E1 – packet switching E.g. Frame relay, ISDN – Wireless E.g. 4G, 5G wifi, satellite – Broadband E.g. ADSL, Cable, – Optical E.g. NBN, fibre optics wikipedia/leased_line 21  Device: Router Faculty of Information Technology More intelligent than other devices because it looks at the IP address in the messages. A Router decides on the next destination of a message(a packet) A simple router could be your home router (which is technically a router + a modem ) Larger routers can be found in ISP's 22  How do routers work? Faculty of Information Technology Routers use routing rules to decide how to forward/transmit the messages Various algorithms & standards (Routing protocols) exist – Eg: RIP, BGP & so on The Unix command “traceroute” will trace the route to the destination host. e.g traceroute www.smh.com.au – On windows use the tracert.exe command ) 23  Web applications Faculty of Information Technology Web page development – HTML/XHTML – CSS: Cascading Style Sheets Web Infrastructure – Internet Infrastructure – Web servers Web Applications – Online media and file sharing – Communications – Search engines Human Computer Interaction – History of the Internet 31268 – Web Systems 24 Web servers: Client- Server Faculty of Information Technology Typically many clients make use of a server. The server provides some shared resource. e.g. powerful processing, large disk, database. 25 Two-Tier: Client-Server Faculty of Information Technology Fat client: where most of the processing is done at the client side. Just the data is on the server. – E.g. Microsoft Access  SQL server Thin client: where just the presentation is done at the client and the processing is at the server side. – E.g.Browser  Web Server 26 Three-tier architecture Faculty of Information Technology Sometimes add a middle tier – more scalable – more security (eg: behind firewall) – Often used for dynamic web sites E.g. Shopping website: – 1st Tier: Client: The HTML/Javascript – 2nd Tier: Web server running PHP – 3rd Tier: Database server storing orders, inventory 27 The 3-Tier Model – an Example Faculty of Information Technology Client Presentation/ Processing/ User Interface Business Logic Database PC Web Server/ Database running Application Server a browser Server (Oracle, (IE, (Apache webserver MySQL, file Firefox with PHP) system) etc) 28 Three-Tier Web Site Faculty of Information Technology Not just retrieval of static HTML pages Typically the HTML page is generated dynamically when the HTTP request comes. This dynamic generation is done in the processing tier – or business logic. Generally some of the content of the dynamically generated pages is drawn from a database. 29  Three-Tier (cont.) Faculty of Information Technology The second and third tier may or may not be on different computers. Three tier applications don’t always involve Web sites. Advantages: – Modularization – Can make different user interfaces without altering the underlying processing 30 Peer-to-Peer Architecture Faculty of Information Technology Alternative to Client/Server Clients can also be servers! Examples: – Skype, Bittorrent, Gnutella, SETI@Home 31 Peer-to-Peer Architectures Faculty of Faculty of Information Information - Basic Model Technology Technology 1. All equal clients 32 Peer-to-Peer Architectures Faculty of Information - Hybrid Model Technology 1. Use tracker to locate file... 2. Start downloading from peer.... 33 P2P: Distributed Processing Faculty of Information Technology Idle computers on the Internet are a powerful processing resource. Idea is to use this resource for carrying out many (important) computations. A processing task is broken up into many parts and distributed to participating computers. SETI@home, Google compute, Community Grid http://www.worldcommunitygrid.org/ http://en.wikipedia.org/wiki/World_Community_Grid 34  Web applications Faculty of Information Technology Web page development – HTML/XHTML – CSS: Cascading Style Sheets Web Infrastructure – Internet Infrastructure – Web servers Web Applications – Online media and file sharing – Communications – Search engines Human Computer Interaction – History of the Internet 31268 – Web Systems 35  Web Applications Faculty of Information Technology World Wide Web == network + applications + people Having a network by itself is pretty useless We use applications on top of the network every day  Web browser !! But, web applications are more than just browsing.  Example 1: Online media Faculty of Information Technology Example http://www.smh.com.au Content continually changing Monitoring visitors Targeting advertisements according to pages visited. Generic browser interaction - HTTP+HTML/CSS... 31268 – Web Systems 37  Example 2: file sharing Faculty of Information Technology FTP : started 1971, along with Unix Napster (1999), Gnutella, Bittorrent: Music and video being transferred between PCs Complex technology – not just HTTP 31268 – Web Systems 38  Faculty of Information Example 3: Peer-to-Peer Technology High interest due to some notorious file swapping apps. Three common categories of peer-to-peer: 1. File swapping e.g. Bittorrent, Napster, Gnutella, Infrasearch 2. Instant messaging e.g. AOL Instant Messenger, MSN Messenger, IRC, twitter 3. Distributed processing e.g. SETI@Home Bitcoin has peer-to-peer aspects  P2P: File Swapping Faculty of Information Technology Some protocols published, some not. Incompatible protocols –> separate file swapping communities. – Gnutella protocol is published – Leads to many independently written peer programs that are interoperable e.g. LimeWire, Bearshare, ToadNode – Bittorrent is now more popular –  solves privacy issues with Gnuetta & Napster  Communications Faculty of Information Technology Oldest: Email Established 1972 (Unix) 2006 - 2.5 billion emails/day http://ask.yahoo.com/20060324.html 2010 – 294 billion/day ie: 90 trillion/year! http://email.about.com/od/emailtrivia/f/emails_per_day. htm About 2.8 million/second! Estimated 90% spam Approx 1.9 Billion users 31268 – Web Systems 42 Email takes 28% of workers time.. Faculty of Information Technology  Communications Faculty of Information Technology Newest: VoIP – Internet telephone and videoconf Computer to Computer Computer to/from telephone/mobile Voice Video Text messages, Chat Began with Skype: had 500+ million user accounts! Over 14% of telephone calls Many more other options now: WhatsApp, telegram, 31268 – Web Systems messenger, Facetime, Zoom… 44  Search engines Faculty of Information Technology Example: Google Google's computer visits web sites , and follows their links - “Web crawling” – Creates an index matching combinations of words with the URL (http addresses) – For each search, it ranks web sites according to other website's links to them. – Earns revenue by displaying advertisements aligned with the user's search 31268 – Web Systems 46  Web applications Faculty of Information Technology Web page development – HTML/XHTML – CSS: Cascading Style Sheets Web Infrastructure – Internet Infrastructure – Web servers Web Applications – Online media and file sharing – Communications – Search engines Human Computer Interaction – History of the Internet 31268 – Web Systems 47  Faculty of Information Technology History of the Internet http://www.fcc.gov/omd/history/intern et/  Computers and Communication Faculty of Information Technology Originally the computer was a sophisticated calculator. – Very costly,  each computer needed to be shared by more than one person. Email – 1972: When Unix was developed, it became an acknowledged function of the computer to be used for communication. The effectiveness of computers is a result of the architecture of the Internet. 31268 – Web Systems 49  Faculty of Information Defense Department APRA Technology 1957 US Defense Department thinks academics in USSR are more successful than academics in USA. Defense Dept pays ARPA to fix the problem. ARPA decides to use computers for communication instead of just for computation. Note: ARPA = Advanced Research Projects Agency  Faculty of Information RAND corporation Technology See http://www.rand.org/ National Security research organization 1960’s Paul Baran decides that a network will only survive an atomic bomb if: 1. Data between computers has many paths – Routing 2. Data is cut up in little blocks, each of which goes on its own journey - Packet Switching  Faculty of Information Paul Baran’s Research Technology "On Distributed Communications: 1. Introduction to Distributed Communications Network“ suggests a distributed communication network is most likely to survive atomic bombs.  Faculty of Information Internet Routing Technology Data going from one IP address to another. Router forwards packets from one network to another. Packets of the same file can take different paths. What kind of network is it?  Small World Faculty of Information Technology or Six Degrees of Separation  The world has 6.9 billion people  (April 11 estimate) Harvard psychologist Stanley Milgram shows by experiment that any two people are at most 6 friends apart… 6 degrees of separation Faculty of Information Technology See: www.linkedin.com or facebook.com  Relationship Graph Faculty of Information Technology  Assume we only directly know friends, and indirectly friends- of-friend & so on…  Relationship graph should look random  …. After all, how can we know 6.8 Billion people????  Faculty of Information BUT! Regular Friendship Clustering Technology Clustering: you just know your friends, and their friends. If everyone on earth has 100 friends distance between two people on earth would be 68 million??. Graph from: http://www.ascusc.org/jcmc/vol8/ issue4/scharnhorst.html  Faculty of Information Small World Graph Technology In the real world: Some people have a few friends far away. Some people have a lot of friends. Even this small randomness can be shown to bring the distance from 60 http://getoutfoxed.com/node/62 million down to 6.  Faculty of Information The Internet is a Small World Technology Detailed nonmathematical explanation. Mathematical explanation http://cablemap.info https://www.telegeography.com/telecom-resources/map-gallery/global-internet-map-2011/  The Internet is a Small Faculty of Information Technology World Instead of friends…. Nodes are hosts, hubs, switches… Lines are Ethernet, ADSL, cable… We communicate over the lines using a networking protocol e.g TCP/IP  Faculty of Information Conclusion Technology We’ve provided a teaser about networking Learn more in 31270 Network Essentials Do MAJ03445 Internetworking for far more