Wowza how to invoke an exteral URL when stream start or stop stream?

Call external URL to notify events when stream started or stopped in Wowza. Wowza Streaming Engine (known as Wowza Media Server) is a unified streaming media server software developed by Wowza Media Systems. The server is used for streaming of live and on-demand video, audio, and rich Internet applications over IP networks to desktop, laptop, and tablet computers, mobile devices, IPTV set-top boxes, internet-connected TV sets, game consoles, and other network-connected devices. The server is a Java application deployable on most operating systems.