The core, largely based on IP while still carrying older non–Voice over Internet Protocol (VoIP) voice traffic, transmits the largest concentration of traffic in public networks. 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 transmitted 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 and 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 networks 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.
Core networks also carry circuit-switched voice and T1/E1 and T3/E3 traffic. Circuit-switched voice is an older technology that guarantees a path for each voice call by setting up a dedicated path for the duration of each call.
