What protocol does VoIP use to ensure voice quality?

VoIP commonly uses the Real-time Transport Protocol (RTP) to ensure voice quality during transmission. RTP is designed for real-time applications and provides mechanisms for payload type identification, sequence numbering, and time-stamping, which help manage the delivery of voice packets. Additionally, protocols like the Session Initiation Protocol (SIP) are used for establishing and controlling the communication sessions. Quality of Service (QoS) techniques may also be implemented to prioritize voice traffic over other types of data, further enhancing voice quality.