The following are BSR types :
SHORT BSR and LONG BSR, Padding BSR.
Based on frequency of Transmission there are two types .. one is periodic and another is aperiodic.
Short BSR :
If the BSR is avilable for only one LCG then UE will send short BSR i.e only 8bits of BSR.For the required bytes of grant corresponding index in defined in MAC spec so UE will send index to enb (0 to 63).
Long BSR :
If the BSR is available for more than one LCG then UE will send Long BSR, That is MAX of 24bits which will represent the MAX of 4LCG BSR.
Padding BSR :
To send the BSR ENB will give grant , padding = (grant - (BSR +Header ) if padding is greater than BSR size then it will be called as padding BSR.
Periodic BSR is timer based BSR which will be configured by upper layers. aperiodic BSR is whenever UE has data it will send.