FreeSWITCH (from now on FS) provides a very powerful tool to interact with it: the Event Socket (ESL), made available via the mod_event_socket module ( https://freeswitch.org/confluence/display/FREESWITCH/mod_event_socket ). ESL is a TCP socket where applications can connect to, and perform two types of action: 1. Send commands. 2. Subscribe to events. The applications subscribing to events will receive the expected notifications through the same TCP connection. A simple protocol and transport made it possible for various libraries in various languages to be written. Events from FS can serve multiple purposes. In this article I'm interested in monitoring and event correlation. Homer ( http://sipcapture.org/ ) is a widely used, open source tool to monitor RTC infrastructures. It has a multitude of features, but the core is the ability to collect SIP signalling and other events from RTC applications, and perform a form of correlation. In particular, it's ab...