This Recommendation specifies the minimum criteria for objective speech quality assessment models that predict the impact of observed IP network impairments on the one-way listening quality experienced by the end-user in IP/UDP/RTP-based 3.1 kHz narrowband telephony applications (3.1 kHz narrowband in the main body, 7 kHz wideband in Annex B). Models compliant with this Recommendation predict Mean Opinion Scores (MOS) on the ACR Listening Quality scale. It is expected that the primary applications for such models are monitoring of transmission quality for operations and maintenance purposes, and measurements in support of service level agreements (SLAs) between service providers and their customers. P.564 conformant models may be deployed both in end-point locations and at mid-network monitoring points. This Recommendation includes an electronic attachment containing the test vectors.