I recently added HDLC framing support to the DUP11 and DPV11 devices in
open_simh. This has only so far been tested with DECnet-Plus on VMS.
I wrote up another couple of examples, showing how to use HDLC as a DECnet
datalink, and also how to try a basic configuration of VAX P.S.I. for X.25
communication.
They're here:
https://notlikethatlikethis.blogspot.com/