[HECnet] Decnet over internet

[Paul Koning]

> On Feb 24, 2020, at 9:44 PM, Peter Lothberg <roll at Stupi.SE> wrote:
> 
> 
> I would not recomend DDCMP over TCP, as you have no idea what the 
> TCP implementaion does for timers etc and TCP is streams, you need 
> to identify the packet boundaries.

DDCMP over TCP has been part of SIMH for quite some time.

The stream nature is not an issue, of course.  DDCMP over wires also has a stream physical layer and knows how to do packet framing perfectly well.  The answer is the same in both places: header CRC framing.

> DDCMP over UDP gives DDCMP full control over retransmit timers etc
> for making the connection reliable and what the actual netwrk is doing
> is visible to the DDCMP layer. 

That's true.  Then again, DDCMP does not have any congestion control or timer adjustment or other things that are useful when sending frames over IP network as opposed to fixed delay wires that don't congest.  

As I mentioned, if you have PyDECnet at both ends, you can use DDCMP over UDP.  If you're using SIMH, you're limited to what it implements, which is DDCMP over TCP.

	paul