One of the most important user experiences in networking applications is the perception of responsiveness. If end-users feel that an application is slow, it is often the case that it is slow to respond to them, rather than being directly related to network speed. This is a particular issue for real-time applications such as audio/video conferencing systems and must be prioritised in applications such as remote medical services and off-campus teaching facilities. It can be difficult to quantitatively define an acceptable figure for response times as the requirements may vary from application to application.
However, some applications have relatively well-defined "physiological" bounds beyond which the responsiveness feeling vanishes. For example, for voice conversations, a (round-trip) delay of 150ms is practically unnoticeable, but an only slightly larger delay is typically felt as very intrusive.
– Main.SimonLeinen - 07 Apr 2006 - 23 Aug 2007