A closer look at network structure: ▣network edge: applications and hosts ▣network core: routers network of networks ▣access networks, physical media: communication links (通信链路) Introduction 1-11 Introduction 1-11 A closer look at network structure: ❑ network edge: applications and hosts ❑ network core: ❖ routers ❖ network of networks ❑ access networks, physical media: communication links （通信链路）