SQL & PL/SQL :: Cumulative Total - Passing Parameter Value

i have a table empl which have three column (name,period,attendance)if we pass parameter which value is based on period column

like :January

then out should come sum of all attendence of january group by name like that

name attendance
a60.00
b20.00
c20.00
w40.00

if we pass parameter value :February then attendance should come sum of (January and February) and if we pass parameter March then attendance should come sum of(January,February and march)

create table empl (name varchar2(10),period varchar2(10),attendance number)
insert into empl values('a','January',20)
insert into empl values('a','January',10)
insert into empl values('a','January',30)
insert into empl values('a','February',20)
insert into empl values('a','March',60)
insert into empl values('b','January',20)
insert into empl values('c','January',20)
insert into empl values('w','January',40)