Lightning Server and/or f.e. Minim server provides the content upon request to the Lightning DS app in your iOS-product. When you point your Lightning DS app to a particular library for the first time, a request for contents is made. The response is not a file per se, rather a flow of information. Lightning DS then creates a local index in your device for this library. This means that you need to “build an index” in your iPhone even if you already did this on your iPad earlier.
Linn Kazoo o.t.o.h requests information in real time from the selected library i think, which means it does not build a local index and therefore is more reliant on network speed and response from the media server.
I had some difficulties in grasping these basics at first but i’m getting there!