Why I don't just use a DreamPi
Up to this point, I’ve not mentioned the DreamPi for this whole networked game thing I’m doing. The reason is pretty straightforward; I have more than one Dreamcast to test with. DreamPi is a great solution for a single unit, though trying to scale it to more than two is troublesome. I’d like to see someone create a HAT for the Pi to do this with support for four units at once, but it would be an incredibly niche thing. I digress.
When I started this, the initial plan was to use a spare computer, install a lightweight distribution on it, create a bunch of line voltage inducers, and as many modems as I could fit in there. That was until I thought about the masses of 9V batteries (or other power solution) and general hassle it would cause. Though, it would be a fun project, in all honesty. Also I happened to come across a great document that came with the R11 SDK called IntraSet.pdf. It describes an intranet setup for dial-up connections on a mass scale for a game that was at a trade show. Presumably the setup was for either one game with many sessions hosted (if so, it’s highly likely that was Quake III Arena) or many games with a few sessions. Either way, the setup was for 96 consoles to connect to one network. The end solution to this comprised of a switch, two PortMaster 3s, four Adtran TSU 600es, and a computer to act as a gateway. For a much smaller setup, I figured one of each would do just fine.
So, what is an Adtran TSU 600e and a PortMaster 3, anyway?
The Adtran TSU 600e is a T1/FT1 multiplexer which has six slots for various types of modules. The type that’s of use to the Dreamcast’s modem is the FXS (Foreign Exchange Subscriber) module. This allows for the dial tone, ring voltage, and battery current required. It’s very similar to the wall socket which would normally be used. Each of these modules provides four RJ11 sockets, totalling a maximum of 24 per unit. The e variant of the TSU 600 provides a 10Mbit Ethernet connection for remote management.
A PortMaster 3 is an integrated access server. For the purposes of connecting Dreamcasts together, it contains a set of digital modems and a connection to a T1 line.
Connecting all of this together is pretty simple. The switch connects to the computer acting as a gateway, the PortMaster 3, and (optionally) the Adtran TSU 600e. Then the PortMaster 3 and Adtran TSU 600e are connected via the T1 line. The PortMaster is responsible for assigning IP addresses and the Adtran for making the physical connection.
That is my long-winded way of attempting to describe why a DreamPi isn’t the solution for this particular setup.