regarding data transfers

hi,

can anybody tell me when we use SESSION METHOD,CALL TRANSACTION and LSMW.

urgent plz,

some say that for small amout of data we use CALL TRANSATION and for large volume of data we use SESSION METHOD .but i don't understand how many records is small and how many records is large. and for what type we use LSMW.

full points will be rewarded.

regards,

kiran