1.2 The 4-Layer Internet Model

• Internet: end-hosts, link, and routers

  • Data delivered hop-by-hop over each link in turn

    • In packet: data, header (from, to)

• Link layer: carry data over one link at a time

  • E.x. ethernet, WiFi

• Network layer: deliver packets end-to-end across the Internet from the source to the destination

  • Network layer packets: datagrams

  • Hands datagrams to the Link Layer, telling it to send the datagram over the first link

    • Link layer provides service to the network layer

  • Special

    • Must use the Internet Protocol (IP)

      • IP makes a best-effort attempt to deliver datagrams to the other end, but no promises

      • IP datagrams can get lost, can be delivered out of order, and can be corrupted. No guarantees

• Transport Layer

  • TCP: transmission Control Protocol

    • Ensure orders

    • Provides service to application that guarantees correct, in-order delivery of the data running on top of the network layers

  • UDP: user datagram protocol

    • No delivery guarantees

• Application Layer

  • Typically, Bi-directional, reliable byte stream

• Numbering system:

  • Network layer: layer 3

  • Ethernet: layer 2

  • Application: layer 7