We have been experiencing intermittent/temporary ADSL PPPOA dropouts at a couple of sites.
Typically the ADSL modem is an Actiontec GT701 although we have also used an old Wirespeed and a Cisco 1710.
The test to recreate the problem:
Set up a continuing ping to a couple of remote sites.
Start a large file ftp transfer OUT of the local site. i.e. an "upload".
(Outgoing emails with larger attachments seem to cause the problem during normal operations).
With the ftp transfer going we see a few ping dropouts and then a total dropout.
The modem drops the PPPOA connection when this happens.
The problem solves itself after 20, 30 or 40 seconds - depending on the particular configuration of modem, etc. and this interruption time will be rather constant from outage to outage.
This happened at one site in July and we made it better / acceptable by changing the modem from PPPOE to PPPOA and assigning a public IP address to the modem.
Then it started happening a couple of weeks ago at another site about 50 miles away.
The telco and the ISP are the same at both sites and things become common at some point before or when reaching the ISP equipment.
I have good contact / communication with the ISP and only third-hand via the ISP with the telco.
We are all scratching our heads as to what must be happening and what we might do about it.
Rule out all of our office site equipment.
I can connect a bare laptop directly to the modem and recreate the problem.