[Freeswitch-users] Monitoring Uptime: landline-->VOIP-Provider-->freeSWITCH-->landline case?

Hello, I need advice - what kind of monitoring or testing applications (OS,free) do you know for testing the uptime of a VOIP landline number provider and phones (voip + landline) behind a freeSWITCH ? Since this post is a start for a educational journey I am also glad for literature documentation regarding monitoring of telephone system, preferable with open source applications. All the best Arfst