End-To-End packet delay is one of the canonical metrics in Internet Protocol (IP) networks, and is important both from the network operator and application performance points of view. For example the quality of TCP IP is directly
dependent on delay, and network providers may have Service Level Agreements specifying allowable values of delay
Statistics across the domains they control.
An important component of end-to-end delay is that due to forwarding elements, the fundamental building block of which is the delay incurred when a packet passes through a single IP router. All input and output links were monitored, allowing a complete picture of congestion and in particular router delays, to be obtained. Packet delays and congestion are fundamentally linked, as the former occur precisely because periods of temporary resource starvation, or micro congestion episodes, are dealt with via buffering.