the services that are carried over the network. Are voice calls clear? Are videos being successfully received with high quality, without stalls and pixilation? Are customers able to rapidly access web content? End-to-end service or application monitoring provides measurements that attempt to cap- ture that end-to-end user experience-from source to destination, across the wide range of diverse end points and across different services and applications. Service performance monitoring is challenging to scale, courtesy of the vast number of end points and the wide range of services and applications. There are two primary techniques that exist-active and passive monitoring. Active probes send test traffic across networks, emulating customer services; passive probes "listen in" to customer traffic to provide aggregated visibility into customer experience. Both are typically leveraged in large-scale networks in a bid to construct a good view of how the services are performing, aggregated across customers. Data collectors operating on ONAP are responsible for collecting the logs, traps, counters, and service monitoring measurements required for operation tasks (and beyond), and for passing the measurements to long-term storage for historical analyses. ONAP can also leverage the mea- surements for a range of real-time operational tasks, including real-time capacity management, identifying network and service performance conditions, and validating change management activities. 15.2.3.3 Control Loops: Repairing Network Impairments and Resolving Customer Impact ONAP control loops, as defined in Chapter 7, are integral to fault and performance management, as well as real-time capacity management and even traffic management. The basic function of a control loop is to detect, isolate, and mitigate issues, whether these are "hard failures" (e.g., network and/ or services are "down"), "soft failures" (performance degradations), or capacity crunches. Ideally, issues can be mitigated via automated responses, such as by rebooting a v