The PSTN is a network that connects customer equipment together through lines, trunks, and switches to allow communication. It has four major elements: customer premises equipment, the access system, transport, and signaling. The access system provides the wiring that connects customer equipment to the central network, including lines and trunks. It terminates at central office equipment. The transport component transmits signals through the core of the network using various transmission speeds and media between switches. A cellular call placed to a landline passes through the radio access network, mobile switching office, and the PSTN using its lines, trunks, and switches to connect the calls.