o we manage this risk while balancing the speed of new technology introduction? Scalable testing of new technologies before they are deployed, and controlled introduction of technologies in the field mitigates risk. However, keeping pace with the speed of change necessitates that as much of this testing and field validation be as automated as possible. As both the data and control planes are being simultaneously updated, and with new poli- cies being introduced to manage alarming and event correlation, we can expect that operations teams may not always have perfect visibility into network impairments. However, as discussed in Section 15.2.3.3, end-to-end service monitoring can be used to detect customer-impacting issues, which may otherwise fly under operations' radar. Such monitoring tests the integrity of the end-to-end service paths; inherently covering both the physical and virtual network tech- nologies. Note that to be able to relate end-to-end service measurements with VNF and PNFs, we must have detailed end-to-end service paths, which fully describe how traffic is carried across virtual and physical elements (VNFs and PNFs) and across network layers. These can be nontrivial to obtain, but are vital to being able to relate end-to-end measurements with relevant network observations. 15.4.2 BOOTSTRAPPING SDN/NFV DEPLOYMENTS LEVERAGING CURRENT KNOWLEDGE AND EXPERIENCE There is tremendous domain knowledge and expertise that has been gained by carriers in operat- ing legacy PNF technologies. Much of this experience will be relevant in the new, software-centric VNF environment. How can we prime the new ecosystem to leverage the benefits and experience of the past? Today, policies exist in the legacy OSSs that manage today's networks-for example, correlation rules for alarm dampening and event localization/root cause analysis. As physical net- work elements are replaced by VNFs, we may be able to leverage such policies in the new world. The complexity of transforming legacy rules to apply them to VNFs depends on 