ice traffic, transmits the largest concentration of traffic in public net- works. It transmits packetized voice (VoIP), non-VoIP voice traffic, data, and video traffic between switches on high-speed fiber-optic cabling. Traffic in the core is trans- mitted across countries and continents and dropped off at wiring centers and Points of Presence (POPs) from where it is routed via Metropolitan Area Networks (MANs) and last-mile networks to subscribers. From there, either the traffic is handed off to other carriers or the long-haul carrier might transmit it over MANs directly to residential business customers. Carriers also transmit data and VoIP traffic between enterprise sites on long-haul networks. Special arrangements are made with these customers for optional services such as security and priority treatment for voice and video conferencing. These net- works are considered part of a carrier's private data networks. They are separate from the Internet and offer guaranteed speeds and low latency (no or unnoticeable levels of delay) on an end-to-end basis. For more on this, see Chapter 5, "Broadband and Wide Area Network Services." Core networks also carry circuit-switched voice and T1/E1 and T3/E3 traffic. Cir- cuit-switched voice is an older technology that guarantees a path for each voice call Long-Haul Networks: The Core by setting up a dedicated path for the duration of each call. See the section "Circuit- Switched Voice and T1/T3 over Fiber," later in this chapter, for more on circuit-switched voice. T1/E1 and T3/E3 traffic is based on Time-Division Multiplexing (TDM), which, like circuit switching, guarantees time slots for all calls and data traffic. See Chapter 5 for more information on T1/E1 and T3/E3. Transoceanic Network Systems Intercontinental voice and data traffic is carried over hundreds of undersea cables. TeleGeography (a division of PriMetrica, Inc.) is a telecom market research firm located in Washington, DC. In April 2010, it profiled 228 active international under- sea systems. The number of n