adding an HDLC device driver to Fusion's IP stack

HI,I’m working on the NS7520 with NETOS v 6.0 and I would like to connect my HDLC driver device to the TCP/IP stack (add it to the network device table) . Do you know which parameter I have to set in the field devFamily ? in the documentation it is said that we only have the choice between AF_PPP and AF_ENET (for Ethernet) . Best regards