 true data rate, in fact regardless of whether data are being sent at all. For this reason, various green mechanisms have been proposed that save energy by putting ports into sleep mode when there are no data to be sent. Other proposed mech- anisms include automatically adjusting transmitted power according to cable length, and automatically adapting transmission speed according to the amount of data that need to be sent. IEEE has standardized the first mechanism as energy-efficient Ethernet (clause 78 of IEEE 802.3). When there are no data to be sent the physical layer sends low power idle (LPI) symbols for some specified time, and then enters sleep mode during which it only transmits periodic refresh signals to maintain link integrity, although all receive circuitry remains active. When new data arrive, the normal idle signal is sent for some time, and transmission is subsequently restored. 6.6.5 Higher Layers As we have mentioned above, 3GPP specifications severely underspecify the transport seg- ments within the NG-RAN and between the gNB and the 5GC, viewing connections from the cell site to the core as transparent transport pipes. In practice, this connection is imple- mented as a non-trivial collection of transport segments and NEs, often operated by multi- ple network operators, each with its own technologies, management systems, and business interests. This state of affairs is the result of two sets of justifications. The first set consists of technological constraints that make it unappealing to simply connect base stations to the core network. Ports on core routers are limited in number and expensive - there are simply too many cell sites for it to be economically feasible to directly connect them all to core elements. Even were there sufficient ports, the number of fibers required for a star configuration from core edge routers would be prohibitive. Core elements have very high rate ports (e.g. 100 Gbps), which are unneeded and too expensive to implement for cell site equipment. Finally, provision of 