[Simh] LAVC

[Mark Pizzolato]

On Saturday, March 11, 2017 at 10:06 AM, Johnny Billquist wrote:
> On 2017-03-11 17:18, Mark Pizzolato wrote:
> > On Saturday, March 11, 2017 at 5:49 AM, Tim Stark wrote:
> >> Thanks for many replies. I learned a lot about VAX clustering. I will
> >> use multicast Ethernet for clustering.  I have more one question. Is
> >> that possible to emulate HSC controllers with LAVC access?
> >
> > When Matt Burke and I were discussing the CI concept, we picked IP
> > Multicast as transport for the very specific reason that all modern
> > host systems will have natural user mode programming access to
> > implement this functionality.  Attempting to create your own Ethernet
> > multicast protocol (non-IP based) will have portability complexities
> > on different platforms due to the fact different platforms have
> > varying support (and potentially require privilege) to present and/or
> > receive raw Ethernet frames to/from a LAN.
> 
> I don't know for sure, but I assume that Tim just meant that he will let LAVC
> do as LAVC does, without him doing anything.
> And LAVC itself might be using ethernet multicasting.
> This is no more an issue than DECnet communication, which also requires
> access to the raw ethernet.

True.  It could use the existing raw Ethernet access methods, but that approach 
would have the following issues:
	1) Some platforms require significant privilege (root) to do this.
	2) He would have to re-invent much of what LAVC does.
	3) The same problems that exist today on *nix hosts to provide a 
mechanism for multiple simulators running on the same host to be able to
concurrently communicate with each other will exist.

An IP multicast based solution lets the host OS solve much of this.

- Mark