A Computational Perspective on Network Coding

Figure 3

(a) A simple multicast network with two terminals has only one encoding node; (b) A feasible multicast network with two terminals has two encoding nodes. But it is not a simple multicast network, because if we delete $(v_1,v_3)$ and $(v_2,v_4)$, this multicast network is also feasible.

(a)

(b)