"This Recommendation describes a subjective test methodology which is able to assess and diagnose the quality of speech in a ""telephone conversation"" scenario. Common conversation tests@ as described in [ITU-T P.800] and [ITU-T P.805]@ provide valid methods for the overall conversational quality@ but do not give insights into reasons for possible quality losses. In addition@ common conversational tests lack analytic ability@ since na?ve participants concentrate on the conversation flow. To circumvent these problems@ this Recommendation describes a test methodology that specifically allows participants to perceive each phase of a conversation separately@ in addition to a natural conversation@ and yields overall conversational quality scores as well as quality scores for each phase (listening@ speaking@ interaction). In addition@ scores for seven underlying perceptual dimensions of conversational speech quality are provided. These scores enable the analysis of conversational speech quality for diagnosis and optimization."