[atlas] Algortithm for probe detecting its offline

Hi, I wanted to ask what is the algorithm / methodology used for a probe detecting / reporting it is offline? I ask, because this morning I intentionally rebooted my cable modem on the network the probe is attached to, which brought my internet down for about 1-2 minutes (I was using the internet immediately after the cable modem re-synched), but the probe is reporting that outage as a 29 minute outage rather than a few minutes. Any comments on why there should be such a large variance from my actual experience versus what the probe saw? -Greg