16 2因特网 23因特网交换点( Internet eXchange Point,IXP) POP #3 Tier 1 Networks Tier 2 Networks Transit IXP POP #2 PoP #1 Tier 2 ISP Transit Transit Tier 3 Network Tier 3 Network (multi-homed ISP) (single homed ISP Internet users (business, consumers, etc) 河南中医学院/阮晓龙/13938215080 ke xuewen ci河南中医学院 / 阮晓龙 / 13938213680 / http://ke.51xueweb.cn 2.因特网 16 2.3因特网交换点（Internet eXchange Point，IXP）