I'm on CAT Telecom ADSL2+ and every single time there is a power cut my modem lose contact with the DSLAM. When power is back then the connection resumes after a few minutes.

I thought the new DSLAM boxes had some type of UPS attached?

(I have UPS for my modem/router and computer, but to no avail...)

I'm not sure your conclusion is correct. We would need a lot more detail, information. I'm not clear why your local loss of power translates into the same loss of power at a CoLo, perhaps 2 Km away?

But, it is easy to imagine that CAT, and others, do not consider residential xDSL to be mission-critical, thus requiring battery/generator back-up. Also you could be on a street-side cabinet, which does not have battery back-up. I've seen a lot of the new elevated True street-side cabinets, and TOT cabs, they do not have battery back-up.

Have you reviewed your contract? Does it guarantee some percentage of uptime? Have you contacted them regarding your issue? If so, what did they say?

Check what goes down during a power cut, the dsl circuit or the ppp connection. If the DSL connection goes down you lose the entire connection of course, and a DSLAM module usually takes about 3 minutes to start up again.

Best place to check if the local loop is on power backup, is your local CAT office, as it is their responsibility. The call-center doesn't have this information. Afaik, CAT doesn't use UPSes but separate chargers/inverters with batteries attached (which lasts way longer than a household UPS).

If it's just the PPP connection, the problem can be anywhere, as there's at least 3 devices between your router and the one that hands out your IP address.

If your applications require an improvement in WAN uptime you could consider a dual-WAN/3G router, which can utilize a 3G modem (some have this incorporated into the platform, so you plug in a SIM) on auto-failover, so when you lose your DSL line you can roll-over to a mobile-broadband connection like 3G or 2G. There have been several threads here on these devices, along with some recommendations and experiences.

It is the same with TRUE.

If we have a very local (our sub-soi only) power cut ADSL remains on but if the cut also covers our main soi (DSLAM is located at the mouth of the soi 1.5km from us) ADSL goes down and it takes 3-5 minutes to come back up after power has been restored.