nes its own inter- nal clock, and like a master initiates its own PTP messaging. In normal operation PTP is used at update rate sufficient to precisely set its internal clock frequency, SO that time determinations can be extrapolated for some time. However, fre- quency adjustment made at packet rates is necessarily less accurate than that obtainable via a PLL working on the physical layer. That being said, it is possible to combine highly accurate frequency obtained from SyncE with less frequent time updates obtained from PTP (1588wSyncE). It should be mentioned that in order to conform to the more stringent requirements of 5G, new techniques are still being developed. PTP has undergone a revision to 1588v3, which includes both new security mechanisms and higher accuracy through the so-called white 6 Enabling Technologies rabbit extensions (ITU-T 1588v3). In order to cope with brownfield networks that do not use SyncE and/or do not have PTP on-path support, the distributed GM (DGM) approach may be used (US 9,276,689). DGM breaks the paradigm of a single master clock located relatively remote from its slaves (and thus suffering from numerous uncompensated time errors from all the intermediate switches), and instead uses a large number of PTP masters close to the cell sites where the slaves are located. These devices are presently available in small form-factors to simplify deployment. 6.6.4.5 Energy Efficiency Studies estimate that between 0.5 and 1% of global electric energy consumption is directly attributable to mobile communications, of which about 20% is consumed by the transport segment. Power consumption can be taken to be linearly proportional to data rate (note that energy consumption of computation increases super-linearly with clock speed). Hence, 5G's striving to increase rates by a factor of 10-100 will lead to a dramatic impact on global power consumption, unless power efficiency is improved. All physical layer technologies used for xHaul transport consume essentially constant power regardless of the