An edge switch is positioned at the physical edge of a public network.The user organization gains access to an edge switch via an access link, or local loop. A central office (CO) is an example of an edge switch in the context of the circuit-switched Public Switched Telephone Network (PSTN). In the context of asynchronous transfer mode (ATM), an edge switch may be referred to as an access node or service node. See also ATM, CO, local loop, switch, tandem switch, and PSTN.