关键词：电子信息；网络安全；协议
摘 要：A network can be considered as the physical resource for a communication system. This chapter introduces network security protocols. In Chapter 7, we introduced the basic mechanisms for establishing protected communications. In this chapter, we use these mechanisms to establish protected communications at a specific layer.As we said, a layer represents a communication protocol and is tasked with a specific function or a specific service. At each layer, a header conveys instructions on where to deliver the data and how to process it.