This ITU-T Recommendation provides specifications for transmission time, including delay due to equipment processing time as well as propagation delay, in connections with echo adequately controlled. Recognizing that delay became a limited resource in modern networks, this ITU-T Recommendation is intended to assist network operators and transmission planners as well as equipment manufacturers in controlling the detrimental effects of pure delay (even if echo is perfectly controlled) on end-to-end speech transmission quality. All applications with overall performance which depend on user or terminal interactivity are concerned.