On 12/20/11 20:20 , Greg B - NANOG wrote:

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?

At the moment, we use a rather simplistic method and that is the connection to the controller. That connection is often re-established within 3 minutes, but it may also take much longer. Note that the probe continues doing measurements while the connection to the connection to the controller is down, so when it is back up it is possible to verify what happened exactly. We are trying to figure out where that delay is coming from, but at the moment we don't have the answer yet.