Wow boy. I'm not sure. I have a cable modem. I love it. But
it has failed. And when it did they said I would have to wait
a week to have it fixed. My heart sank. I get so much email
that this would cause a serious problem. My mail server can
not be off-line for a week.
So, I installed an ISDN backup system. Luckily this is easy for me.
For many people this would be hard/impossible/expensive. The good new
is that my cable modem came back to life the next day. It turns out
that for a while it was flakey when it rained (I now understand this
is not an uncommon phenomena for cable modems).