This Recommendation describes relationships among the following ITU-T Recommendations: G.781, G.783, G.798, G.803, G.810, G.811, G.812, G.813, G.821, G.822, G.823, G.824, G.825, G.826, G.827, G.828, G.829, G.921, G.8201, G.8251, I.350, I.352, I.353, I.354, I.355, I.356, I.357, I.358, I.359, I.381, Y.1530, Y.1540, Y.1541, Y.1560 and Y.1561. Collectively, these Recommendations provide the basis for the specification and apportionment of performance in narrow-band and broadband ISDNs, Internet Protocol (IP)-based networks, and digital layers of transport networks. They include jitter, wander, and network synchronization and timing performance. These Recommendations are intended to be used in describing performance between the measurement points that delimit and apportion international ISDNs, IP-based networks, and digital layers of transport networks.