LTE: What is the use of polling at RLC layer ?

Question

While going through 3GPP 36.322 specification. I saw a routing box inside the figure. Can anyone please explain the uses of it ?

Answer 1

An AM RLC entity can poll its peer AM RLC entity in order to trigger STATUS reporting at the peer AM RLC entity for the transmitted RLC AMD PDU.

Answer 2

The transmitting side of the AM RLC entity can proactively request a status report from the peer receiving side by polling using a 1-bit indicator in the AM RLC header. The transmitting side can then use the status reports to select the RLC Data PDUs to be re-transmitted, and manage transmission and re-transmission buffers efficiently.

Typical circumstances in which the transmitting side may initiate a poll include, for example, the last PDU in the transmitting side having been transmitted, or a predefined number of PDUs or data bytes having been transmitted.

When the receiving side of the AM RLC entity receives a poll from the peer transmitting side, it checks the reception buffer status and transmits a status report at the earliest transmission opportunity.