From the perspective of end-hosts, network is like a black-box. The status of current network is mostly stored in the core, rather than the edge. In order to let end-hosts be aware of current network status, a host need to know i) the topology of the network, and the path of its flows, ii) the flows of other hosts that share the links with its flows.
The topology is easy to acquire, as long as the network is relatively small (comparing to internet) or structural, e.g., datacenter network. Besides, to know which link a host is using, i.e., the path of its own flows, the routing policy should also be acquired.
Flow information of other hosts can be acquired by FSTs. Which will be discuss in section x.x.x.