https://www.juniper.net/documentation/en_US/junos/topics/concept/fusion-software.html
SNOS is like linecard firmware image
Fusion “brain”, which runs the actual control plane functionality
JFE supports PoE, .1x, and stacking/clustering for the SD Vchassis.
JFD has e.g. local switching capability in the SD etc.
JFD:
JFE: