The network edge: ▣end systems(hosts): run application programs e.g.Web,email at "edge of network" ▣client/,server model client host requests,receives service from always-on server e.g.Web browser/server; email client/server 口peer-peer(对等网络)model:: minimal (or no)use of dedicated(专用的)servers e.g.Skype,BitTorrent,KaZaA Introduction 1-12Introduction 1 -12 The network edge: ❑ end systems (hosts): ❖ run application programs ❖ e.g. Web, email ❖ at “edge of network” ❑ client/server model ❖ client host requests, receives service from always -on server ❖ e.g. Web browser/server; email client/server ❑ peer -peer （对等网络 ）model: ❖ minimal (or no) use of dedicated （专用的） servers ❖ e.g. Skype, BitTorrent, KaZaA