1. Internet and Protocols

(1) Internet

The Internet connects spatially separate hosts, allowing different hosts to share resources and exchange information

(2) Agreement

Protocol Defines the communication rules between network devices, which is equivalent to the communication modes between devices (similar to the communication modes between humans).

It defines the format and order in which network devices receive and send information and the actions taken by network devices when receiving and sending information

Delay and loss

(1) the delay

Why does the packet delay? After a packet is sent from a terminal, it can be forwarded through multiple routes before reaching the destination terminal

The delay of a packet in a route is called nodal delay and includes processing delay, queuing delay, transmission delay and propagation delay

  • Processing delay: Check whether there is an error and determine the route exit
  • Queuing delay: Queuing for transmission at the route egress. The queuing delay depends on route congestion
  • Transmission Delay: Transmits data packets out of a route. The delay is equal to the size of the data packet/the egress bandwidth
  • Propagation Delay: To transmit packets to the next route. The delay is equal to transmission length/propagation speed

(2) lost

Why are packets lost? As we know, the cache capacity in routing is limited, and it is impossible to queue countless packets at the same time

If the cache of the packet reaches the route is full, the route rejects the packet, causing the packet to be lost

3. Layered protocols

(1) Seven-layer model (conceptual model)

The seven-layer Model is also known as the ISO/OSI Reference Model.

It is proposed by ISO network interconnection model, its purpose is to make the world’s computers can be connected to each other into a network

The seven-layer model consists of application layer, presentation layer, session layer, transport layer, network layer, link layer and physical layer from top to bottom

(2) Five-layer model (application model)

Transmission Control Protocol/Internet Protocol Model (TCP/IP)

The TCP/IP protocol cluster is currently the core protocol of the Internet. In fact, they are not only referring to TCP and IP, but are synonymous with a group of protocols

The five-layer protocol consists of the application layer (combining the first three layers in the seven-layer model into one layer), transport layer, network layer, link layer, and physical layer

(3) Why stratification

Because the Internet is a very complex system, layering can reduce the coupling degree between components and improve the maintainability of the network system

Each layer is responsible for specific functions. The following describes the functions of each layer in the TCP/IP protocol model:

  • Application Layer: The interface between applications and network services
  • Transport layer: Provides logical inter-process data transfer services
  • Network layer: provides logical data transfer services between hosts
  • Link Layer: Physical addressing that turns a bit stream into a logical transmission line
  • Physical layer: Controls the transmission of bitstreams