  Measurement has become fundamental to the operation of networks and at-scale
services---whether for management, security, diagnostics, optimization, or
simply enhancing our collective understanding of the Internet as a complex
system. Further, measurements are useful across points of view---from end hosts
to enterprise networks and data centers to the wide area Internet. We observe
that many measurements are decoupled from the protocols and applications they
are designed to illuminate. Worse, current measurement practice often involves
the exploitation of side-effects and unintended features of the network, or, in
other words, the artful piling of hacks atop one another. This state of affairs
is a direct result of the relative paucity of diagnostic and measurement
capabilities built into today's network stack.
  Given our modern dependence on ubiquitous measurement, we propose
measurability as an explicit low-level goal of current protocol design, and
argue that measurements should be available to all network protocols throughout
the stack. We seek to generalize the idea of measurement within protocols,
e.g., the way in which TCP relies on measurement to drive its end-to-end
behavior. Rhetorically, we pose the question: what if the stack had been built
with measurability and diagnostic support in mind? We start from a set of
principles for explicit measurability, and define primitives that, were they
supported by the stack, would not only provide a solid foundation for protocol
design going forward, but also reduce the cost and increase the accuracy of
measuring the network.
