merge timestamps to intervals

Hi!

I have a table where I repeatingly log the status of some service, which
looks something like this:

	< timestamp, status >

Now, everytime my service is up I save the timestamp and a status of
"up", if it's down I save the timestamp with "down", eg:
	10:13	up
	10:14	up
	10:15	up
	10:16	down
	10:17	up
	10:18	up

I'd like to merge this information to intervals where the service was up
or down.

	< intervall, status >
	10:13-10:15	up
	10:16-10:16	down
	10:17-1018	up

I've no clue how to approach this problem.

Any ideas/hints?

Thanks
Patrick