As a point of information, here is a map I saw (posted elsewhere) of the area that this occurred in: Turkish territory dips into Syria. I suppose it would be relatively easy for a Russian aircraft to have 'accidentally" flown over Turkish territory if it was operating in the area. You generally don't have nicely drawn lines on the ground to know exactly where the border is. And if you are flying at ~10,000 feet while doing 500-1000 mph you could overfly that Turkish finger of land wihout realizing it. If the Turkish Air Force did issue 10 warnings over a 5 minute period (as was mentioned in an article I read somewhere) before they shot at the aircraft, this should have been ample enough warning to have de-escalated the issue.