An EJB method named Aby calls another EJB method named Bob
Bob is marked with @TransactionAttribute(TransactionAttributeT
Actually, I think alternative a is correct. See:
EJB 3.0 - Nested Transaction != Requires New?
I have also done some research and looked into the db (Hyper Sonic) logs to actually see when it is committed in the db and it is committed when the REQUIRES_NEW method is finished. But since it's up to the container to handle the transactions maybe it could change depending on container. I've used JBoss while debugging this. And Hibernate (worth mentioning since I've tested this by checking db logs). I presume that a database write is involved since you ask about transactions.
My thoughts differs from the previous answer so it would be fun to be persuaded.