hi Mythili,
work experience is must , if you want to do MBA in top schools,in USA,Canada, 2 years is must and UK they look for 3 years work exp, also few school take freshers too, which are not top schools, they will consider only your GPA/percentage and you would be studying wid freshers.
GMAT is mandatory only if you want to do MBA in America and canada, which is 2 years MBA.
Europe MBA is 1 year MBA.
for UK/Europe only few schools ask for GMAT,
CAT is recognized only in India, GMAT is globally , GMAT would be an add-on in your application, CAT and GMAT is almost the same when you think how tough it is.
all the best