UE sends these three different types of BSR's (Short, Long and Truncated) as MAC Control elements and it adds LCG ID and not LC ID in them along with Buffer Size.
And the answer for your question is below
- Short BSR and Truncated BSR format: one LCG ID field and one corresponding Buffer Size field (figure 22.214.171.124-1); or
- Long BSR format: four Buffer Size fields, corresponding to LCG IDs #0 through #3 (figure 126.96.36.199-2).
Refer to 36.321 spec 188.8.131.52 for details, Happy Reading!!!