tional requirements, such as provision of distributed computational platforms, and co-existence with or migra- tion from existing network infrastructures. 6.6.4 The Physical Layer In this subsection we will discuss a plethora of physical layer technologies that have been proposed to face the challenges presented by 5G transport. Figure 6.6.4 provides a prelimi- nary overview of the proposed technologies and the challenges addressed by each. 6.6 Transport Network 10 GbE, XGS-PON - but 10 Gbps is only satisfactory for initial 5G deployments 25 GbE (802.3by), 1-lane 50 GbE (802.3cd) 100/200/400 GbE (802.3bs, 802.3ck) high data rates FlexE Mobile (Multi-access) Edge Computing Synchronization (SyncE., IEEE 1588, DGM) low latency Network slicing Time Sensitive Networking (and Deterministic Networking) Frame Replication and Elimination (IEEE 802.1CB) ultra high reliability Figure 6.6.4 Summary of mechanisms for upgrading the xHaul physical layer. 6.6.4.1 Achieving the Required Data Rates While achieving a 10- to 100-fold increase in data rate is well understood to be challeng- ing for the air interface, it is far from trivial for xHaul transport as well. LTE backhaul is mostly based on GbE interfaces (whether fiber or point-to-point microwave) with even lower-rate synchronous digital hierarchy (SDH) and even plesiochronous digital hierarchy (PDH) still in common use. Physical links supporting data rates of up to 1 Gbps will not suffice for 5G needs (and even for LTE-A, which may approach 3 Gbps). The duct itself, whether active/passive optical or microwave, may require technology upgrading. In the near term (Release-15 with eMBB traffic) it is expected that cell site backhauling (i.e. the NG interface) will peak at about 5 Gbps. Such data rates are readily handled by upgrading 1 Gbps Ethernet transport links to 10 Gbps ones, an upgrade that involves limited CAPEX (the existing fiber plant will support 10G, and 10G SFP+ [enhanced small form-factor pluggables] are no longer appreciably more expensive than 1G SFPs) and ins