rks as well as the demand of the latest wireless standards for smaller and higher bandwidth cells, the use of fiber connec- tivity has become more prevalent. Depending on the demarcation point between key net- work elements, one can decide whether fiber should be used only as a high data rate backhaul path or a transition to radio-over-fiber techniques can be afforded for the fronthaul links, as well. Backhaul traffic comprises a number of components in addition to the user-plane traffic. As the transport networks evolve, network operators are evalu- ating and, in some cases, have already started to deploy mobile fronthaul networks to support centralized RANs and ultimately C-RANs. In these networks, the BBU is moved from the cell site to a central location. This creates a new fronthaul network between the BBU and the cell site that has typically utilized CPRI protocol until just recently, which effectively carry digitized RF signals. These networks require fiber-based back- haul of Ethernet traffic from either the cell site or the BBU location, regardless of the last mile technology. The last mile could be the same Ethernet-over-fiber connection or Ethernet over some other media such as copper or microwave. As the cell topology changes from a traditional macro-cell to smaller cells, the requirements for the endpoint of the backhaul service typically become more stringent to meet certain deployment spe- cifications such as temperature range, space, and power consumption. The performance of the underlying transport network must substantially improve in order to support the considerably tighter transport performance requirements in terms of frequency synchroni- zation, phase synchronization, and latency. Since the performance of the backhaul net- works is becoming more critical to end-to-end 5G services/applications, performance monitoring capabilities are imperative to ensure that the QoS requirements and service- level agreements are met (see Fig. 1.39). 5G Network Architecture External networks Aggregation netwo