School me on hub and spoke federations

[Mike Flynn]

Was recently asked to look at Kennisnet.nl as federation for another client.  Looking at their fed they call it a "hub and spoke" federation.  Their metadata only consists of a single SP/Idp pair that Kennisnet maintains.  Does not look to work like the more traditional federations (a'la InCommon etc).

Google has been pretty worthless trying to get information on how this type of federation works.  Can anyone enlighten me?
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