FRF.9
FRF.9 classifies packets into two types: control packets and data packets. Control packets are used for status negotiation between the two ends of DLCI where the compression protocol has been configured. FRF.9 data packets cannot be switched before the negotiation succeeds. If FRF.9 fails to negotiate the state after ten FRF.9 control packets are sent, the negotiating parties stop negotiation and the compression configuration does not take effect.
FRF.9 compresses only data packets and InARP packets; it does not compress LMI packets.
FRF.9 stac compression is suitable for low-speed links.