Systems with MCDN can be networked ad-infitum, or at least until the dest codes/routing is extinguished. 1-SL1 in, 1-SL1 out per system, with another trunk module as a local PRI. As long as the routing is correct and the trunks can access each other, then you can have calls flowing all kinds of directions until the channels are full.
Unfortunately with the MICS and SL1 programming there is no TAT/TRO as there is with VOIP (which is system to system). But in essence I could create a routing loop (think the old intranet "ring" structure rather than a "mesh" structure) in this sense. Because I can create DEST CODES and ROUTE entries on a per system bases that will direct enough calls to max out the trunks needed, which would be 23 channels point-to-point.
--DB