QoS is a technology that allows you to assign a priority level to different types of traffic and optimize the transmission process. Thus, high-priority data (e.g. IP telephony, video communication) are transmitted first and with minimal delay, while low-priority data (e.g. file transfer) are queued and transmitted when the channel becomes available.
QoS technology allows improving the quality of information transmission. It is most effective in those cases when the resources of network communication are limited or the connection is unstable.