cost and performance. A central- ized node can serve more cells and as the load in these cells can vary, it can reduce hardware costs by resource pooling and sharing. Moreover, as the centralized node has larger visibil- ity into more cells and UEs in these cells, it provides improved RRM and better scheduling (to an extent, as the scheduler itself is not centralized). However, these gains often come 4 NG-RAN Architecture at a cost of potentially increased latency and more stringent requirements on the transport network. Such architecture was used in 3G, where one centralized RNC controls multiple dis- tributed Node Bs. In LTE, 3GPP moved away from this architecture and designed E-UTRAN as a "flat" network with a single network node - the eNB. With the advent of 5G, history repeats itself and the RAN architecture evolves from hierarchical 3G architecture, through flat LTE architecture, to hierarchical architecture once again in 5G. It is important to point out that even though the standardized E-UTRAN architecture in LTE is flat, some vendors have implemented split RAN architectures. Obviously, in such implementations network nodes are connected via proprietary interfaces, which makes it impossible to deploy equipment from different vendors in the same network. One of the intentions of the 3GPP standardization process is to allow a split NG-RAN implementation with standardized interfaces, to allow multi-vendor deployments. Such an interface has been defined; however, it remains to be seen whether actual multi-vendor NG-RAN deployments materialize. In the past, operators had the tendency of deploying equipment from a single vendor in a given area, in order to minimize interop- erability issues. This may or may not change in 5G, as operators are increasingly interested in using equipment from multiple vendors to drive down costs. Moreover, there are new companies trying to exploit that desire to enter the marker. On the other hand, "mixing and matching" equipment from different vendors shifts the burden of interope