INFT132 093 02 Internet Concepts


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Internet Concepts

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INFT132 093 02 Internet Concepts

  1. 1. INFT11/71-132 Web Applications Internet Concepts Dr Michael Rees School of Information Technology
  2. 2. The Internet • The Internet is a global, wide area network (WAN) of computers • Composed of millions of smaller local area networks (LANs) all connected together • All computers support Internet Protocol (IP) • Each computer must have a unique IP address: a unique 32 bit value made up of 4 numbers (each 0-255) • Example IP Address: – Binary: 11101110.00010001.10011111.00000100 – Decimal: © 2009 Michael Rees Web Applications 2
  3. 3. Internet Protocol • Transfer data from source device to destination device (computers today but any device in future – the Internet of Things) • IP source software creates a packet representing the data: – About 1500 characters – Header: source and destination IP addresses, length of data, and so on – Data itself – Checksum used to test data integrity and correct transmission • If destination is on another LAN, packet is sent to a gateway or router that connects one network to another © 2009 Michael Rees Web Applications 3
  4. 4. Packet switched network • TCP (Transfer Control Protocol) breaks data into packets at the sending end and reassembled at the receiving end • Packets pass from a source computer, possibly through several intermediate computers to the destination computer • Computers acting as routers examine the packets and decide the onward path each packet should travel © 2009 Michael Rees Web Applications 4
  5. 5. Transmission Control Protocol • TCP overcomes the limitations of IP: – No guarantee of packet delivery (packets can be dropped) – Communication is one-way (source to destination) • TCP adds concept of a connection on top of IP: – Provides guarantee that packets are delivered – Provide two-way (full duplex) communication © 2009 Michael Rees Web Applications 5
  6. 6. TCP Handshake Can I talk to you? Establish connection { OK. Can I talk to you? OK Here’s a packet Send packet with acknowledgment { Source Got it Destination Here’s a packet Resend packet if no (or delayed) acknowledgment { Here’s a resent packet Got it © 2009 Michael Rees Web Applications 6
  7. 7. TCP Ports • TCP also adds concept of a port • TCP header contains port number representing an application program on the destination computer • Some port numbers have standard meanings • Other port numbers are available first-come-first served to any application © 2009 Michael Rees Web Applications 7
  8. 8. TCP Ports • Port numbers identify particular services on an Internet host computer • Examples: – port 25 used for SMTP (mail transfers) – port 23 used for TELNET (remote host connection) – port 80 used for HTTP (web page transfers) © 2009 Michael Rees Web Applications 8
  9. 9. User Datagram Protocol - UDP • Like TCP in that: – Builds on IP – Provides port concept • Unlike TCP in that: – No connection concept – No transmission guarantee • Advantage of UDP vs. TCP: – Lightweight, so faster for one-time messages © 2009 Michael Rees Web Applications 9
  10. 10. Domain Name Service - DNS • DNS RFC • DNS is the “phone book” for the Internet – Map between host names and IP addresses – DNS often uses UDP for communication • Host names – Labels separated by dots: • – Final label is a top-level domain • Generic: .com, .org, .tv, .name • Country-code: .au, .us, .il © 2009 Michael Rees Web Applications 10
  11. 11. Domain Name System • Allows human-readable domain names to map to IP addresses (try: nslookup • Used in Universal Resource Locator (URL): domain file protocol folder server is a Fully Qualified Domain Name - FQDN © 2009 Michael Rees Web Applications 11
  12. 12. So, who runs the Internet? • ISOC (The Internet Society) – Is a non profit central organization for the groups that are responsible for the standards for internet structure – • ICANN (Internet Corporation for Assigned Names and Numbers) – • W3C (World Wide Web Consortium) – develops standards for the web – © 2009 Michael Rees Web Applications 12