receive not ready (HDLC) (RNR)

Receive Not Ready (RNR) is a control field in the LAP-B protocol that is used for explicit flow control as well as positive acknowledgement.

With RNR transmission, the sending data station is explicitly informed that a congestion situation exists. The transmitting data station must not continue transmitting after receiving an RNR character.

The RNR command is used to indicate the previous active operating state: for example, RNR 1 indicates that all I-frames up to the one with sequence number 0 have been received correctly, but no reception is possible for the following I- frame. The next data can only be sent at the next Receive Ready( RR). This control character indicates that the jam situation has been cleared again.