I. Network Stratification

  1. OSI’s seven-layer protocol is clear in concept and complete in theory, but complex and impractical.
  2. TCP/IP layer 4 protocol, widely used. In fact, there are only the top three layers, the network interface layer does not have any concrete content.
  3. Five layer protocol, integrated OSI and TCP/IP advantages, generally used to learn computer network principles.

Two layer functions

  1. Application Layer The application layer provides services for user processes directly. There are many protocols in the application layer, including HTTP protocol supporting the World Wide Web, SMTP protocol supporting email, FTP protocol supporting file transfer, etc.
  2. The transport layer is responsible for providing services for communication between processes in two hosts. Since a host can run multiple processes at the same time, the transport layer has the functions of reuse and reuse. Reuse means that multiple application layers can simultaneously use the services of the lower transport layer, while distribution means that the transport layer delivers the received information to the corresponding protocols in the upper application layer. Two main protocols, TCP and UDP, are used in the transport layer.
  3. The network layer is responsible for providing communication services to the two hosts. When sending data, the network layer encapsulates the packet segments or user datagrams generated by the transport layer into packets or packets for transmission. In TCP/IP architecture, packets are also called IP datagrams because IP is used at the network layer. Another task of the network layer is to select an appropriate route so that packets transmitted by the source host transport layer can find the destination host through routers in the network.
  4. When data link layer transmits data between two adjacent nodes, data link layer assembs IP datagrams handed over by network layer into frames, and transmits data in frames transparently on the link between two adjacent nodes. Each frame includes data and necessary control information (synchronization information, address information, error control, etc.).
  5. The physical layer transmits the bit stream, and the physical layer also determines the type of plug to connect the cable. Transport media does not belong to the physical layer.