es use CDNs to replicate their web content at many edge locations to prevent delays at their web or e-commerce sites. For traffic that traverses the Internet backbone, CDNs use mathematical algorithms to map out the best paths for traffic to take. www.TechnicalPDF.com Exchanging Data at Peering Points Large multinational carriers are referred to as Tier 1 carriers. Tier 1 carriers own the majority of the high- speed lines that make up the Internet backbone. These carriers, all of whose networks are international, include Nippon Telegraph and Telephone Corporation (NTT) in Japan; Telefónica in Spain and Latin America; Deutsche Telekom in Germany; France Telecom in France; and AT&T, Sprint, and Verizon in the United States. Regional carriers-which are referred to as Tier 2 carriers-also own core, backbone facilities. Comcast and Charter are considered Tier 2 carriers because their networks do not cover the entire country and they purchase backbone capacity from Tier 1 carriers. These Tier 1 and Tier 2 carriers interconnect with other carriers in places where they do not have coverage. These interconnections are referred to as peering points. Network service providers transfer Internet Protocol (IP) traffic among one another at peering sites. Peering sites are also referred to as Internet exchanges and Network Access Points (NAPs). ISPs lease ports on the routers of other providers as a means of transferring IP traffic between networks. This enables carriers to send traffic that originated from their own customers to areas where they do not have network facilities, as demonstrated in Figure 6-3. Peering Site with Connections between Carriers' Routers www.TechnicalPDF.com Racks with multiple carriers' routers Backup generators Windowless, hurricane-proof building with high levels of security and duplicate power sources Fiber-optic cables to carriers and power sources Figure 6-3 Traffic at peering points is routed between the facilities of multiple network operators. The terms "ISP" and "carrier" are used synonymously