ITU-T Q.552

This Recommendation provides characteristics for 2-wire analogue interfaces, input and output connections with 2-wire analogue interfaces and half-connections with 2-wire analogue interfaces in accordance with definitions given in ITU-T Q.551. This Recommendation is valid for equipment that may terminate an international long-distance connection via 4-wire circuits interconnected by 4-wire exchange. It also includes, in a separate category, characteristics for interfaces which cannot terminate an international connection and are therefore entirely national in application.