I thought 2780 uses BISYNC, which is a different protocol. X.25 is HDLC. Yes, both need modem eliminators -- like an async null modem but an active device that also supplies the synchronous bit clock.
X.25 (and I think HDLC) is indeed asymmetrical. Whether that can be gotten around is not entirely clear to me. I do know X.25 has the concept of "call collision", a protocol failure caused by a protocol design error. It uses a two-way connection handshake, which was well known at the time to be wrong, and both DDCMP and NSP as well as other protocols such as TCP have always used a three-way handshake for that rason. paul > On Mar 19, 2020, at 7:48 PM, John Welsh <johnwe...@optusnet.com.au> wrote: > > Hi Dave, > I have been involved in a project using VAX-2780-3780PE and have been able to > connect two VAX’s together using a Black Box Synchronous Modem Eliminator ( > SME ). > Product code: ME204A-F. > No VAX PSI involved. > Needed Decnet Plus and Wan drivers. > > Was able to test using a utility that comes with the Protocol Emulator - > XJTEST which can use either VAX as a loopback. > In my case it was a DSV11 to a DSW42 using the SME and the V.24 cables that > come with the adapters. > There is also another utility called REMOTE that can transfer simple files > from VAX to VAX. > I don’t think there is a driver for SIMH that can emulate a sync device. ( > yet ). > > Regards, > John Welsh. > > Sent from my iPhone > >> On 20 Mar 2020, at 03:38, dave porter <dave_list_a...@verizon.net> wrote: >> >> I know almost nothing about VAX PSI, but I have a vague idea >> that even though X.25 is asymmetric and intended for DTE to DCE >> communication (i.e., your computer to the phone company's premises), it may >> be possible to coerce it >> into talking from one VAX to another (via null modem >> cable connecting two devices such as DUP-11s). >> >> I worked on RSX-11M PSI and that's how we tested in >> the lab. I can no longer remember how that was done. >> Undocumented option somewhere, no doubt. >> >> >> _______________________________________________ >> Simh mailing list >> Simh@trailing-edge.com >> http://mailman.trailing-edge.com/mailman/listinfo/simh > > _______________________________________________ > Simh mailing list > Simh@trailing-edge.com > http://mailman.trailing-edge.com/mailman/listinfo/simh _______________________________________________ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh