ignificant additional OPEX (less than 1 W difference at 10 or 20 km). However, this remedy comes with three caveats: The first is that those deployments that exploit TDM-based PON technologies will prob- ably have to migrate to active networks. The first available PON standard is XGS-PON [ITU-T G.987.x] at 10 Gbps, which limits the ODN to a single 2 1 split. On the other hand, PONs that utilize wavelength-based multiplexing, including NG-PON2 [ITU-T G.989.3], which can reach 40G rates, will be viable for some time. The second is that 10 Gbps does not suffice for all functional splits, in particular, the F1 interface will require higher data rates even for initial NR deployments; and of course F2 fronthaul traffic may be much higher in volume. The third relates to futureproofing. The quoted 5 Gbps rate is for initial deployments; over time, and especially with deployment of mmWaves and system channel bandwidths of 200 MHz and above, the traffic to and from cell sites is expected to dramatically increase. 10 Gbps will probably suffice in most cases for the first two to three years of 5G deploy- ment, and thus is an attractive upgrade option for existing networks. However, it is ques- tionable whether it makes sense to design new networks (using 5 Gbps transport) that will require re-engineering in several years' time. 6 Enabling Technologies For those cases where 10 Gbps does not suffice, multiplexing of multiple 10G links may make sense. Such multiplexing can be accomplished via link aggregation (LAG) (IEEE 802.1AX), but only when there is some criterion that consistently maps flows and fairly dis- tributes bandwidth between them. For backhauling, standard hashing techniques should suffice, but these methods may not be applicable at the low-level split (Section 4.5) with compressed headers. The next rate to be considered could be the conventional 100 Gbps, although this capacity should not be needed for single cell sites. 100G is already used for LTE second-level aggrega- tion networks, and will be required for 5G