 data rates, lower latency, lower packet loss rate (PLR), and higher reliability. Multiple classes-of-service assured by E2E service and network slicing. Orchestrated dynamic connectivity for on-demand mesh topology embracing multiple physical and virtual components. Zero touch provisioning (ZTP) and automation for dynamic E2E slicing support. Such substantial changes furnish major challenges (both engineering and economical) for a mobile operator to define a smooth migration path for their transport network. In most cases the existing 4G backhaul and aggregation networks will be incrementally enhanced 6.6 Transport Network and upgraded to reach the 5G xHaul end-game. Recent practices indicate that such migra- tion will usually be executed in phases; an example scenario consisting of the following phases: 1. Upgrading to support higher data rates. Integrating the transport network with edge computing (i.e. MEC). 3. Decreasing latency and increasing reliability. 4. Adding support for slicing (different traffic types over a single network infrastructure). 5. Assuring higher density of UEs for IoT (optionally integrated with 4G IoT deployment). 6.6.3 Defining the Problem At the highest level of abstraction, a 5G network consists of three entities: 5G UE; 5G NG-RAN, incorporating gNBs and ng-eNBs (described in Chapter 4) and other ele- ments to be described later in this section; 5GC, described in Section 3.2. In many cases there is also a catch-all fourth entity - external DNs or server platforms. 5G communications are carried out by inter-connecting these entities. 3GPP standards (3GPP 38.401) specify that the RAN consists of a radio network layer (RNL) and a transport network layer (TNL), where the TNL provides services for transport of both user plane and signaling. 3GPP specifications deal in minute detail with all aspects of RNL connectivity between the gNB and 5GC (and among gNBs), but severely underspecify¹2 the TNL aspects of these, viewing connections from the cell site to the core as ideal transport pipes.