When organizations are unable to communicate directly with one another because of legal limits or national boundaries, existing federations can negotiate inter-federation federations which allow members of different federations to interact with one another.
Examples: REFEDS, eduGAIN, and Kalmar2 are inter-federation programs for research institutions and higher education.
When to use: Institutions are unable to form direct relationships with one another because of legal or national boundaries, but have existing federations that can negotiate on their behalf.
Advantages: Federations can act as agents, negotiating for members to simplify the complexity of getting agreement among a large number of institutions.
Disadvantages: The complexity of negotiating inter-federation agreements slows the process and may limit the interactions that are covered.
The full papers is downloadable [Field-Guide-Internet-TrustID] Here is a link to introduction of the paper and a at the bottom of that post is a link to all the other models with descriptions. Below are links to all the different models.