System learning TCP/IP protocol (I) ------ useful policies and modes

System learning TCP/IP protocol (I) ------ useful policies and pattern protocols are actually a strategy and pattern to solve some problems, there are many policies and modes worth learning in the classic TCP/IP protocol. In summary, there are some of the following (more and more): hierarchical encapsulation and reliable connection layering are the core policies and modes of TCP/IP and network communication, layered, so that all network applications do not need to care about the details of the underlying link transmission, but also make different types of networks communicate effectively. This is a typical method of simplifying things and decomposing complicated things into different layers of strategies. The relationship between layers is the relationship between services and services, each layer only needs to focus on the dimensions. For example, different types of networks are interconnected through the abstraction and processing of the network layer IP protocol, and the underlying transmission differences are transparent to the upper layer (transport layer and application layer, this brings great convenience to the Development of upper-layer applications, as shown in the following: encapsulation and reuse in order to implement and support the layer strategy mentioned above, TCP/IP adopts encapsulation and sub-use policies in the data packet design. The so-called encapsulation means that some header information is added to each layer during the data transmission process of the application, this information is used to communicate with the acceptor at the same level. For example, when data is sent from an application to the Ethernet, data is processed layer by layer as follows: the processing process at the acceptor is the opposite, that is to say, in the sub-use policy, data is split layer by layer from the underlying layer to the upper layer of the application process, and each layer extracts the information it needs. As shown in: reliable connection TCP uses a three-way handshake to ensure that a connection is established when packet loss is possible, and the connection protocol is reached through mutual confirmation between the two parties. In addition, the fault tolerance process is implemented for both parties through a very refined state flow. These design details can be used for reference in multi-system interaction design.