[HECnet] Multics online as node 1.770 (BANAI)

[Paul Koning]

> On Sep 7, 2018, at 5:03 PM, Jeffrey H. Johnson <jhj at trnsz.com> wrote:
> 
>> On Sep 7, 2018, at 1:00 PM, Paul Koning <paulkoning at comcast.net> wrote:
>> 
>>> On Sep 6, 2018, at 7:47 PM, Jeffrey H. Johnson <jhj at trnsz.com> wrote:
>>> 
>>> [snip] virtual hobbyist Telenet/Tymnet-like PSN network for X.25 systems. [snip]
>> 
>> X.25 is basically a datalink layer (HDLC with some tweaks).  What would such a virtual network look like?  I figure something like tunneling X.25 semantics over TCP, or something along those lines.  Or sending approximate X.25 PDUs over UDP, the way the SIMH DDCMP implementation does for that data link.
> 
> My idea was a little lower level, hoping to use emulated serial links (tunneled over TCP links and thus error free) to create point-to-point connections in a way that would be compatible with Dynamips, so I could leverage the Cisco IOS X.25 support for the DCE (provider) side of the network.

Do you mean the X.25 client packets, or the bits coming out the bottom of X.25?  The former is straightforward so long as the clients send multiples of 8 bits.  The bottom of X.25 is not quite so simple since HDLC is a bit stream datalink, not a byte stream like Ethernet or DDCMP.

The analogs you could draw on: for the client side, that's like the "Simulated DMC" that appeared for a short while in SIMH 3.9 and can still be found in my PyDECnet.  For the bottom of the datalink, the current DDCMP emulation in SIMH is a good model.  I suppose you probably would not do bit stuffing.  Not a multiple of 8 bits could still be handled if needed.

	paul