etwork (WAN) acceleration, wherein specialized compres- sion and protocol optimization decrease delays. See Chapter 1 for more information on WAN acceleration. 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 Cor- poration (NTT) in Japan, Telefónica in Spain and Latin America, Deutsche Telekom in Germany, France Telecom in France, and AT&T and Verizon in the United States. Regional carriers-which are referred to as Tier 2 carriers-also own core, back- bone facilities. Comcast and tw telecom 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 6-2. The terms "ISP" and "carrier" are used synonymously. Carriers that own peering points charge other carriers for connections to ports on their routers. However, traffic at these peering centers has the potential to create delays in the Internet if carriers lease too few ports from one another in an attempt to save money. If carriers exchange about the same amount of traffic, they often don't charge one another under this arrangement. Security, routing, traffic policing, and Network Address Translation (NAT) take place at peering points