poll/final bit (P/F)

In the HDLC protocol, each frame has a P/F bit (poll/final bit). The poll bit is part of a command frame, while the final bit only occurs in response frames. In general, the P/F bits have the status 0. If the poll bit is set in a command frame, it must be answered by a response frame with the final bit set. In the case of a poll bit set in the I-frame, the acknowledgement of the opposite side must be made with a Receive Ready ( RR), Receive Not Ready ( RNR) or Reject ( REJ).