So...Complexity Driver 1: Roaming


So it is the subscriber binding to a "home" service provider, with provider-mediated roaming to the networks of other providers that is at the root of the complexity here

Any such provider-controlled roaming scheme must accommodate SIX parties, with at least THREE accounting/billing relationships, all of which must be tracked in the control plane, the data plane, and management plane. 
Which control, data, and management planes?

What are the six parties and the accounting/billing (A/B) relationships?