21 2因特网 23因特网交换点( nternet eXchange Point,ⅨP) ahttp://en.wikipedia.org/wiki/internetexchangepoint a An Internet exchange point( X or IXP)is a physical infrastructure through which Internet service providers(ISPs) exchange Internet traffic between their networks(autonomous systems) o IXPs reduce the portion of an iSPs traffic which must be delivered via their upstream transit providers, thereby reducing the average per-bit delivery cost of their service. Furthermore, the increased number of paths learned through the IXP improves routing efficiency and fault-tolerance 河南中医药大学/阮晓龙713938213680/http://network.xg.hactcm.edu.cr