What is the Internet?

Internet
1. It is a computer network that interconnects billions of computing devices through (called hosts/end systems) the world. From a service point of view, the Internet is an infrastructure that provides services to applications.
3. Components
  1. Host (end system)
  2. Communication links
    1. Connect end systems. Transmission rate is measured in bits/second.
      1. Transmission rate (b/s)
    2. Types of physical media
      1. Coaxial cable
      2. Optical fiber
      3. Radio spectrum
      4. Copper wire
  3. Packets
    1. When one end system has data to send to another end system, this data is segmented and to each segment header bytes are added. The resulting packages of information are called packets.
  4. Packet Switch
    1. A packet switch takes a packet arriving on one of its incoming communication links and forwards that packet on one of its outgoing communication links.
    2. Types
      1. Routers
        Typically used in network core
      2. Link-layer switches
        Typically used in access networks
  5. Route (path)
    1. Sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system.
  6. Analogy
    1. Packet-switched network
      1. Packets
        Communication links
        packet switches
        end systems
    2. Transportation networks of highways, roads, and intersections
      1. Trucks
        highways and roads
        intersections
        buildings
  7. Internet Service Providers (ISPs)
    1. They are a network of packet switches and communication links. They provide a variety of types of network access to the end systems.
    2. Examples
      1. Residential ISPs
        Local cable
        Telephone companies
      2. Corporate ISPs
      3. University ISPs
      4. ISPs that provide WiFi access to public places
      5. Cellular data ISPs
    3. Types
      1. Lower-tier ISPs
        They are ISPs that provide access to end systems. They are interconnected through national and international upper-tier ISPs. They are managed independently, run the IP protocol and conform to certain naming and address conventions.
      2. Upper-tier ISPs
        They consist of high-speed routers interconnected with high-speed fiber-optic links. They are connected directly to each other. They are managed independently, run the IP protocol and conform to certain naming and address conventions.
  8. Protocols
    1. Most important protocols in the Internet
      1. Transmission Control Protocol (TCP)
      2. Internet Protocol (IP)
    2. They are standards on how some procedures work in the Internet. They are developed by the Internet Engineering Task Force (IETF) through documents called request for comments (RFCs).
      1. Standards
      2. IETF
      3. RFCs
  9. Distributed applications
    1. They are applications that involve multiple end systems that exchange data with each other. They run on end systems, not in the packet switches in the network core.
  10. Socket interface
    1. They are provided by end systems to specify how a program running on other end system asks the Internet infrastructure to deliver data to the program running on the former end system.
Protocols
1. Human protocol vs Network protocol
2. A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.
Review Questions
1. Review questions
2. Answers

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What is the Internet?

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