On Jun 22, 2012, at 4:07 PM, Rob Jarratt wrote: DDCMP over some kind of serial line? Would need appropriate hardware and driver code to work against that. DDCMP over sync, yes. But DDCMP also works on an async line, and that just requires protocol code that can talk to a raw mode TTY device. That would work for what I need -- I have async DDCMP on my PRO-380 running RSTS, and in fact it's a standard feature of some of the PDP11 DECnet products. (I'm not sure if it was ever official in DECnet/E, but the machinery is there in the latest versions of the kernel.) paul