Quality of Service (QoS)

Quality of Service (QoS) is the set of methods by which network traffic is treated differently according to importance and technical requirements in order to ensure reliable transmission quality for selected applications. The decisive parameters are bandwidth, latency, jitter and packet loss.

The basis is classification: packets are assigned to traffic classes and marked, in IP networks mostly via the DSCP field according to the Differentiated Services (DiffServ) model, in Ethernet networks via priority bits according to IEEE 802.1p. Network devices then treat the classes differently, for example through preferred queues for voice and video. Bandwidth management includes traffic shaping, which smooths data streams, policing, which discards or re-marks excess traffic, and assured minimum and maximum bandwidths per class. An older model with resource reservation per connection is Integrated Services (IntServ).

QoS only works where all network devices involved take the markings into account. On the public internet this is not guaranteed; Software-Defined WAN (SD-WAN) therefore combines local QoS at the sites with the dynamic selection of the most suitable line. Whether the measures reach the users can be verified with Digital Experience Monitoring (DEM).