 first-level aggregation networks. Advancing from 10G to 100G involves a major jump in CAPEX, as 100 Gbps currently comprises four lanes of 25 Gbps. Even for single-mode fiber where these lanes are instantiated as different wave- lengths and not individual fibers, 100G requires a quad small form-factor pluggable (QSFP) with four lasers, making it significantly more expensive than 10G. In addition, 100G stan- dards do not presently support bidirectional traffic on a single fiber (BiDi), and thus require twice the number of fibers when compared with 10G employing BiDi. In addition, NEs that can forward at 100G wirespeed are also significantly more expensive than comparable lower-rate ones. Power costs for 100G are not really that much higher than for 10G. The IEEE, while standardizing 100 Gbps, included an intermediate rate of 40G (clause 80 of IEEE 802.3), but there seems to be little reason to consider this rate. For data centers 40G made sense, but was defeated in the market by 56G Infiniband. For backhauling it presents few advantages compared with deploying 100G, using four lanes and thus being about as expensive as 100G. In 2016 the IEEE approved amendment to 802.3, which standardized a rate of 25 Gbps. A 25G link corresponds to a single lane of the 100G standard, and was thus born with opera- tional experience. Like 10G, 25G interfaces are supported by inexpensive SFP+, and do not require a QSFP. It is thus reasonable to assume that 25G will supplant the 10G links used for initial 5G deployments. Support for 25G and higher rates has recently been added to OTN standards (ITU-T G.709) as well (ITU-T G.709-Amd3). For yet longer-term cell site deployments, for aggregation networks, and for lower func- tional splits, multiplexing of 25G links will be used. The problem of distributing traffic over the 25G links can be solved here by using an emerging standard called FlexE. The Optical Internetworking Forum (OIF) published the original FlexE Interoperability Agreement in 2016 (and an updated one in 2017). Among a h