Forum:KB:Rebel Troops aboard Tantive IV

I can't seem to find this information anywhere so I was wondering-

What is the official title, group, organization, etc. of the rebel troops as seen aboard the Tantive IV at the beginning of ANH? There are pages and pages on Wookieepedia about Stormtroopers and their equipment/armor, but I can't find anything about the affiliation and history of these iconic soldiers. Where did those slope helmets with the visors and the blue shirt/black vest combo come from? Are the Alderaanian soldiers, Corellian? Seriously, who are they?