Two bounds on network coding rates are reviewed that generalize edge-cut bounds on routing rates. The simpler bound is a bidirected cut-set bound which generalizes and improves upon a flow cut-set bound that is standard in networking. It follows that routing is rate-optimal if routing achieves the standard flow cut-set bound. The second bound improves on the cut-set bound, and it involves progressively removing edges from a network graph and checking whether certain strengthened dseparation conditions are satisfied.
Gerhard Kramer, Serap A. Savari