All about Buffer Status Reporting (BSR)

Buffer Status Reporting (BSR) :

- The Buffer Status reporting procedure is used to provide the serving eNB with information about the amount of data available for transmission in the UL buffers of the UE.

Type Of BSR:

- UL data, for a logical channel which belongs to a LCG, becomes available for transmission in the RLC entity or in the PDCP entity and either the data belongs to a logical channel with higher priority than the priorities of the logical channels which belong to any LCG and for which data is already available for transmission, or there is no data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as "Regular BSR".

- UL resources are allocated and number of padding bits is equal to or larger than the size of the Buffer Status Report MAC control element plus its subheader, in which case the BSR is referred below to as "Padding BSR".

- retxBSR-Timer expires and the UE has data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as "Regular BSR"

- periodicBSR-Timer expires, in which case the BSR is referred below to as "Periodic BSR".

When UE will Report Which Type:

- periodicBSR-Timer expires, "Periodic BSR".

For Regular and Periodic BSR:

 If (More than one LCG has data available for transmission in the TTI where the BSR is transmitted)

      Report Long BSR.

 else,

      Report Short BSR.

For Padding BSR:

If (Number of padding bits => size of the Short BSR plus its subheader) && If (Number of padding bits < size of the Long BSR plus its subheader)

Then Short BSR or Truncated BSR Can be transmitted instead of Padding.

If (More than one LCG has data available for transmission in the TTI where the BSR is transmitted): 
Then : 

     Report Truncated BSR of the LCG with the highest priority logical channel with data available for transmission;
Else

     Report Short BSR.

Elseif (Number of padding bits => Size of the Long BSR plus its subheader)         

     Report Long BSR.