Modems: resyncs and reboots

I've used various modems on both ADSL and now VDSL. They've run through a UPS which successfully keeps them up through (the occasional) short power outages.

However whilst they've all occasionally resynced (between weekly and monthly or bi-monthly), which is no problem, more or less with different modems this has taken the form of a reboot.

Just out of curiosity, what (other than a power disconnection or manual reset, which are not in issue) causes a modem to reboot rather than just resync? The only noticeable difference I can see is that the log usually just carries on with just a resync, but resets with a reboot. My current modem/router, a FritzBox 7390 running on FTTC (in place of the OR modem) shows an "error report" when the connection comes back up (but I can't access any details) on a resync with a reboot (but not on one without).

In both cases resyncs usually complete within a minute or so. Invariably I'm not using any connected apparatus when this happens, so it's not a problem.

I've a Netgear WNR 2000 running (again through a UPS) on my second fixed wireless service, which occasionally resyncs with the cable modem but has never in over 2 years rebooted (other than after a manual disconnection), so I'm assuming it must be something to do with the characteristics of DSL or the router rather than power supply per se?

EDIT: I suppose it could be the modem just decides its "had enough" and "needs a break"!

Edited by deleted (Tue 10-Jan-12 12:59:34)

The code running in a router, will be such that upon a critical exception (something unexpected) that it will reboot, to clear memory and reload itself.

Consider this, old 15 year old computers when new still needed reboots now and then, and a modern router is not unlike a very slow old computer, i.e. limited CPU and memory resources

In reply to a post by smurf46:

... so I'm assuming it must be something to do with the characteristics of DSL .... rather than power supply per se?

I would suggest that it is more to do with the characteristics of your router.

Specifically, one of my Draytek Routers has an uptime of 1140 hours - during which it has re-synced a number of times.
(and the other has run for much longer than that without a reboot).

Both routers are on a UPS