May I Connect the 3.3V LVDS to Stratix IV 2.5V LVDS directly?

thank FvM!

I saw the development kits of altera corp.

The clock connection is always the 3.3V LVDS for the global Clock input pins.

I thought why not the 2.5V LVDS?

and the 3.3V LVDS must use AC couple, or 2.5V LVDS Can connect directly?

thanks