Last night my beloved plugged a network cable into port 7 of my ZyXEL GS1900-8 VLAN MUX switch and connected the other end to my main LAN switch. At the same time, she unplugged my Firebrick from my main LAN switch.
Now at approximately the same time, so Janet thinks, AA reported a loss of carrier event on each of my four lines. Was this real ? Somehow synchronised across four lines? Or was it something fake connected to what Janet did ? But if the latter, how?
(Unless she unplugged the wrong <something> but then she would have told me and asked for help, and all that does not give me any answer.)
The Johnson stats-logging graph of SNRM over 24 hours shows that there was no resynch / retrain in the modems. I could tell because the SNRM would be seen to reset immediately straight back to the target SNRM at the time of the retrain. So the absence of such evidence suggests that something external / upstream misled AA. There was a very small amount of packet loss shown in the AA CQM graphs after the so-called disconnection came back up. The lines were ‘down’ for 10 min.
How does AA know that the link has dropped? Because the DSLAM reports loss of the link, in some informational message? Or by a time-out in their PPP LCP ping mechanism? If the latter then it could be misnamed when there’s a failure upstream in BT-Land.