IEEE 1394 is Firewire. (Apple's name for it) Do you have an external HDD (HardDiskDrive) hooked up to your computer? Newer computers have A LOT of USB ports but usually just one 1394 on the back and maybe another on the front. I use it because throughput is faster than USB in the real world.
If you do have a Firewire HDD hooked to your computer, then that is why the 1394 is getting turned on automatically all the time. When you unplug the HDD and plug it back in, it will turn it back on. When you re-boot, it will turn the 1394 back on too, if I remember correctly.
There are modems that plug into your computer over a USB port instead of using a Ethernet cable. Some modems (I've never seen one that does) use Firewire to connect to a computer instead of an Ethernet cable.
I agree with johnwill in that it is very doubtful your IEEE 1394 Firewire port has anything to do with your dropping connection.
You might go check out Firewire (IEEE 1394) on Wikipedia: