Is there a method or tool(s) to prove network outages?

Hi Everyone Please I have a very problematic radio link which goes out and back on again every few hours. The only way I know this is happening is from my gateway device: a Sophos UTM that sends email anytime there's been an outage. The ISP refuses to accept this as outage/instability proof, and I'm wondering if there's something I can run behind the gateway UTM that can provide output information over time. They seem to be a primarily Windows+Cisco shop (as is common here in the 4th world). We are primarily Linux. Is there some set of command incantations I can run who's output I can collect and send to them (besides some sort of sustained ping)? Thanks in advance! Sina