m major skyscrapers and office parks to a carrier's equipment. MANs run from a carrier's equipment in towns to Points of Presence (POPs) and wiring centers. A wiring center is a location with a local telephone company switch and connections and electronics for outside cabling. A POP is the location where a switch hands off traffic to long-haul and backbone providers, and vice versa. Middle-mile networks link rural areas to core (backbone) networks. They consist of the fiber or wireless links to backhaul www.TechnicalPDF.com carriers' switches. For the most part, they connect rural areas to inter-city networks and to the Internet. Backhaul refers to "hauling" traffic from local sources to core, backbone networks. These links span hundreds of miles and carry traffic between distant cities. In the United States, backbone networks link Los Angeles to New York City, and Boston to Chicago. Undersea cables that span oceans are also examples of long-haul networks. They carry intercontinental traffic between the United States, Europe, Africa, Australia, New Zealand, and Asia via submarine cables. Because no single telephone, cellular, or cable TV company has service everywhere in the United States or the rest of the world, all providers need connections to and from other telephone companies to transmit voice and data traffic between their own customers, the Internet, the cloud, cellular networks, and customers served by other providers. They additionally need connections to carriers in other countries. CORE NETWORKS-BETWEEN CITIES AND CONTINENTS Core networks, largely based on IP, transmit the highest concentration of traffic in public networks. They transmit packetized voice (VoIP), shrinking amounts of non-VoIP voice traffic, data, and video on high-capacity fiber-optic cabling. Traffic in the core is transmitted across countries, between countries and continents, and under oceans. At multiple points along the route, the traffic is: Dropped off at wiring centers and Points of Presence (POPs) closer to urban and suburban