= The DFA Plugin Architecture =

Access controllers are customized to the underlying testbed technology and testbed policies of a resource provider.  In order to connect custom access controllers we define an interface for creating and manipulating the testbed topologies that experiment controllers use to talk to access controllers.  Access controllers can be integreted into the fedd codebase or be stand-alone controllers that are accessible through these interfaces.

Key to these interfaces is a topology description language, topdl, that defines experiment topologies and sub-topologies at a level of abstraction that can be specialized when necessary.  We discuss topdl below after defining the basic interfaces and terminology.