The direct energy demand of Internet data flows can be assessed using a variety of methodological approaches (top-down, bottom-up, or hybrid/model based) and different definitions of system boundaries. Because of this diversity, results reported in the literature differ by up to two orders of magnitude and are difficult to compare. We present a first assessment that uses a pure bottom-up approach and a system boundary that includes only transmission equipment. The assessment is based on the case study of a 40 megabit per second videoconferencing transmission between Switzerland and Japan, yielding a consumption of 0.2 kilowatt-hours per transmitted gigabyte for 2009, a result that supports the lowest of the existing estimates. We discuss the practical implications of our findings.