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 188.8.131.52-1); or
- Long BSR format: four Buffer Size fields, corresponding to LCG IDs #0 through #3 (figure 184.108.40.206-2).
Refer to 36.321 spec 220.127.116.11 for details, Happy Reading!!!