网络七层结构（Network seven layer structure）.docVIP

网络七层结构（Network seven layer structure） Knowledge base of network seven layer structure The first NO1. OSI model in network interconnection, there are two criteria to consider: legal and factual. Legal means to establish with power or law. That means creating with the actual fact, although there is no official or legal recognition, but for the TCP/IP protocol to create a de facto standard, although before it did not become widely accepted in standard. OSI (Open, SystemInterconnection, open systems interconnection) reference model is a legitimate standard. The international organization for Standardization (ISO) created the OSI model and released it in 1984 to provide vendors with a network model so that their products can work together on the network. The OSI reference model provides a hierarchical analysis tool to understand interconnect technology, as well as the basis for current and future network development. The model also considers interoperability and interoperability challenges faced by DARPA project engineers. The OSI model answers these challenges by means of a 7 tier protocol model, as shown in figure 1-1. By decomposing the model into layers, interoperability and interoperability capabilities can be managed because each layer is self-contained and does not depend on the operating system or other factors. Hierarchical methods also benefit vendors because they simply need to focus their development on the layers of their own products and can build on existing protocols on other layers. Not only does it minimize the cost of development, but also increases the marketability because you can use the products of other vendors. Figure 1-1 OSI reference model The model describes how each layer communicates with the corresponding layers on other nodes. Figure 1-2 illustrates how the data finds its way in the network. At the first node, the end user creates some data and sends it to other nodes, such as e-mail. At the application layer, the application layer header