Kapil, have a look:
Amateur boxing
Headgear is mandatory in modern amateur boxing
: Amateur boxing::
Amateur boxing may be found at the collegiate level, at the Olympic Games and Commonwealth Games, and in many other venues sanctioned by amateur boxing associations. Amateur boxing has a point scoring system that measures the number of clean blows landed rather than physical damage. Bouts consist of three rounds of three minutes in the Olympic and Commonwealth Games, and three rounds of two minutes in a national ABA (Amateur Boxing Association) bout, each with a one-minute interval between rounds
Professional Boxing::
Professional bouts are usually
much longer than amateur bouts, typically ranging from ten to twelve rounds, though four round fights are common for less experienced fighters or club fighters. There are also some two-[14] and three-round professional bouts[15], especially in Australia. Through the early twentieth century, it was common for fights to have unlimited rounds, ending only when one fighter quit, benefiting high-energy fighters like Jack Dempsey. Fifteen rounds remained the internationally recognized limit for championship fights for most of the twentieth century until the early 1980s, when the death of boxer Duk Koo Kim reduced the limit to twelve.
Headgear is not permitted in professional bouts, and boxers are generally allowed to take much more punishment before a fight is halted
http://en.wikipedia.org/wiki/Boxing