1. Network Definition
   1. 终端系统和设备连接的集合，使之可以相互交流
2. Physical Components
   1. PCs,SWs,Routers,Interconnections
3. Network User Applications
   1. Email, Web Browsers,IM, DB,Collaboration(wiki)
4. Resources share & benefits
   1. data & applications
   2. physical resources(camera, printer)
   3. storage devices
   4. backup devices
5. Characterstics of a Network
   1. Speed(Data rate)
   2. Cost
   3. Security
   4. Aviliability
   5. Scalability(可扩展性)
   6. Reliability
      1. MTBF：mean time between failure平均故障间隔时间
   7. Topology
6. Topology
   1. Physical
      1. Bus
      2. Ring
         1. Single/Dual Ring
      3. Star
         1. Mesh and Partial-Mesh
   2. Logical
7. Connection to Internet
   1. DSL:digital subscriber line, telephone line
   2. Cable:television
   3. Serial: CSU/DSU:channel service unit,digital
   4. Modem