Unlike conventional circuit-switched telephone networks, IP networks are packet-oriented. In order to use these networks to transmit time-sensitive services, there are special requirements with respect to Quality of Service. The key parameters describing the service quality of an IP network are latency, jitter and the packet loss rate. Latency refers to the a packet’s delay which occurs end-to-end during transmission. Jitter measures how much latency deviates from a mean. Lastly, the packet loss rate specifies the percentage of IP packets lost during transmission.
Voice-over-IP telephony (VoIP telephony) is a time-sensitive service with specific QoS requirements for the transmitting network. Voice can only be transmitted in a high quality if these requirements are met. To operate telephone systems via IP network or use the services of a cloud telephone system, it is necessary to first verify whether the network is able to provide the required quality of service. Transmission delay and the packet loss rate are particularly key in assessing voice quality. Whilst the loss of individual packets or delays under 100 milliseconds are hardly noticeable by the human ear, high loss rates or delays can result in high communication interference. To ensure the networks are able to meet the QoS requirements, they feature mechanisms to give priority to certain IP packets (voice packets) and delay others.