Quality of Service (QoS) is the ability to control the characteristics of ongoing communication services. QoS encompasses guarantees of available network bandwidth, acceptable data loss (if any), transmission speed, latency, etc. QoS is an end-to-end responsibility that involves clients, switches, routers, and servers.

OPC installations are affected by QoS due to their reliance on acceptable network communication. There are various techniques to help guarantee a given Quality of Service. These depend on the factors that the Network Administrator decides to be most important. For instance, data loss issues can be handled by queuing. This might be acceptable for data archiving applications such Historians. However, this may not be desirable for HMI communication that depends on the ability to view the most recent data without care about old data. In this case, Network Administrators might select a prioritization strategy where the most important data is allowed to pass first. It is even possible to “drop” (lose) data altogether to ensure that significant data is not queued behind optional information.

See also: Bandwidth