摘要: A directed acyclic network is considered where all the terminals need to recover sum of symbols generated at sources. We call such a sum-network. It shown that there exists solvably (and linear solvably) equivalent sum-network for any multiple-unicast network, and thus communication network. also every set polynomials having integer coefficients, which scalar solvable over finite field F if only have common root in F. For or cofinite prime numbers, constructed has vector solution length characteristic alphabet given set. The insufficiency net- work coding unachievability capacity are proved sum-networks by using similar known results networks. Under fractional coding, its reverse be equivalent. However, under nonlinear it whose not solvable.