Handling variable bitrate between origin and edge

How could one handle using a link between an origin and edge server that may have limited bandwidth?

It appears the adaptive bitrate/smil file usage concerns connections between client and edge, and also only works for HLS/HDS and I think rtmp?

In our usage we only have rtsp/udp multicast capablility for the devices that will pull(or receive in the case of multicast) the video from the edge server.

What would be useful is the ability to make a complex smil file like .stream file on the edge (well actually using as an origin I suppose) that would allow the "edge’ application to make the determination which stream to pull from the origin and re-stream udp/rtp over igmp or make available to clients via rtsp, or any other method for that matter.

This is within a closed network, not using cloud services.