Question

Is There any cases that RLC posts the buffer more than grant given by MAC layer? If so, how Mac treats that buffer? And what are futher steps to process that buffer?

Answer 1

When UE has new data arrived in to its buffer then its sends an SR upon receiving the SR eNB sends a grant (can be big / small depends on various factors). In case the received grant is smaller than the data UE has in its buffer UE fills the data based on the grant size it received (should take into account mac header & CE size's too) & then for the remaining data it reports in BSR either Short or Long depending on the number & type of bearers it has.

When eNB receives this BSR it know that UE still has some data in its buffer to transmit so it sends another grant (this grant can accommodate all or a part of UE's data in the buffer ) based on this UE either sends & BSR report saying Zero meaning it doesn't have any data in its buffer or the remaining data

Comments

Hi salil ,

you explained how UE will ask grant, But he is asking how the DL data scheduling will happen.

Actually RLC can ask more grant to MAC but MAC will schedule only the available grant to RLC. First of all RLC wont give more data than grant. Even If RLC gives more data than given MAC will discard those PDU straight away. But as per spec RLC should not give more data than grant, That is the reason grant permission is given to MAC.

Happy Learning :)