I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the operational area directors. Document editors and WG chairs should treat these comments just like any other last call comments.     The document is well written and provides a good description on useful metrics that can be used to measure the performance of network in delivering packets from A to B.     However, for flows traversing various domains of network (which may have  layers of layers tunnels in between), the following aspects need more clarification:     -         Section 2.1: How to measure Flow Size? All the packets sent over the course of the active flow * each packet size? -         Figure 1: Is the Router L closest to A? and Router R closest to B? How those two routers are selected?  there could be many routers between Router L and Router R that have extra large buffer to cause delay, or multiple paths traversing over multiple routers, some of which have larger buffer and others have small, causing jitter.     Cheers,   Linda Dunbar