The acronym QoS stands for the technical term ‘Quality of Service’. QoS defines specific quality requirements which must be met to use a communication service with the desired quality from the subscriber’s perspective. In order to meet these requirements, different actions, parameters and processes are defined depending on the network used or the transfer method, summarised under the term QoS. One can essentially distinguish between the transmission quality and the traffic quality. Whilst the traffic quality primarily pertains to the transmission technology and establishing the connection, the transmission quality pertains to the actual information transfer over a network.

Quality of Service in IP networks

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.

QoS requirements in Voice-over-IP telephony

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.

Further information

Voice over IP: The Art of Switching from PSTN to IP

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