Usually your router or modem will tell you in the connection status / summary where it also lists things like sync speed, line coding (GDMT, G.Lite, ADSL2, etc.).
Or you can ring up your ISP and ask them. They should be able to tell from their end.
Just had it happen again and managed to make my clumsy fingers work quickly enough to do a tracert while it was out.
<code>
C:\Documents and Settings\Kos>tracert www.tehforum.co.uk
Unable to resolve target system name www.tehforum.co.uk.
</code>
:|