Achievable Rate Regions for Network Coding

Determining the achievable rate region for networks using routing, linear coding, or nonlinear coding is thought to be a difficult task in general, and few are known. We describe the achievable rate regions for four interesting networks (completely for three and partially for the fourth). In addition to the known matrix-computation method for proving outer bounds for linear coding, we present a new method that yields actual characteristic-dependent linear rank inequalities from which the desired bounds follow immediately.