#170 Internet & Web basics

The Internet

• The network of networks connected using TCP/IP communication protocol.
• Origin: ARPANET (Advanced Research Project Agency Network)
  • Packet switching network, first to implement TCP/IP
  • Email first available on this
• NSFNET (National Science Foundation Network)
  • First Internet backbone

---

Internet Protocols (IP)

• Designed for use both within LAN (Local Area Networks) and between networks.
• IP addresses
  • IPv4 (32-bit)
    ー associated with at most one device
    ー assigned by IANA (Internet Assigned Numbers Authority)
  • IPv6 (128-bit)
    ー newest version
  • Transfer data packets from source to destination
    ー packets include: IP addresses, length of data, data
    ー packets are sent to gateway that connects to other networks, if there's no destination.
    ー the delivery of packets is not guaranteed

---

Transmission Control Protocol (TCP)

• Adds the notion of a connection
• Implemented on top of IP
• Features
  • Guarantee data packet delivery
  • two-way communication
  • more like telephone rather than postal service
• Also adds the concept of a port
  • header contains port number that represents an application program on the destination computer

---

User Datagram Protocol (UDP)

• UDP vs. TCP
  • Similarities
    ー both are built on IP
    ー both use port
  • Differences
    ー UDP has not connection concept
    ー UDP has no transmission guarantee
• Advantages
  • Lightweight, faster for one-time messages.

---

Domain Name Service (DNS)

• This is like the "phone book" for the Internet
  • It maps between host names to IP addresses
  • Often uses UDP

---

World Wide Web (www)

• World Wide Web is originally proposed by Tim Berners-Lee in 1989
• 3 key ingredients
  • Uniform Resource Locators (URL)
    ー locating documents, built by reusing DNS hostnames
  • Hypertext Markup Language (HTML)
    ー documents
  • Hypertext Transport Protocol (HTTP)
    ー communication
• Internationalized Resource Identifier (IRI)
  • Uniform Resource identifier (URI)
    ー Uniform Resource Locator (URL)
    ー Uniform Resource Name (URN), used to identify resources with unique names like book.