Graduate / What to write in SOP if I dont have any relevent work/project experience? [4]

Hi,
I intend to do MS in field of Distributed systems. But i neither have any relevant work experience nor I did my final year project in this field. Now while writing SOP I face serious question - What to write in SOP & How can I convince admission authorities that I am interested in DS, as I dont have anything to back my claim.

Just saying that "I am interested in DS" without any concrete proof will not be helpful I guess. How should I construct SOP then ?