74 network areas. Those network areas showing natural monopoly characteristics, but no substantial sunk investments, are considered contestable (quadrant 2). Only when natural monopoly characteristics are combined with substantial sunk costs (quadrant 1) should ex-ante regulation be considered. 4.5 Justifying interventions by general competition policy in network industries General competition law applies to all network industries, even if some market segments of these industries are subject to sector-specific regulation. If competition authorities find evidence for the abuse of market power by a market participant, they have the right to intervene into the market. Ex-post intervention by competition authorities is not based on a reference model comparable to the theory of monopolistic bottlenecks. If no monopolistic bottlenecks can be identified ex-ante, then only a case-by-case analysis can disclose those particular circumstances of a market that lend stable market power to a firm. As was argued for the case of sector-specific regulation, competition policy for network industries must also take into account that the nature of competition in network industries is complex. Competitive network markets will show market characteristics of monopolistically competitive markets. Product differentiation and price differentiation tactics make competition in network markets different from competition in markets of homogeneous goods. The traditional antitrust approach of measuring market shares in the relevant product market in order to prove market power is particularly inappropriate for network industries (Knieps, 2006: 70). The alternative methodological approach of using game theoretic models to prove the existence of stable market power in a particular market setting likewise is unsatisfactory in that such models typically simplify and therefore do not reflect the nature of competition in network industries correctly. Furthermore, game-theoretic models typically have multiple solutions (Knieps, 2006: 71). To prove stable market power that allows a dominant firm to make above competitive profits over an extended time period without inducing market entry, competition authorities must show, for a given market constellation, that entry barriers exist that prevent competitors from entering a market in which above competitive profits are being made. This requires a thorough examination of the competition dynamics in the market. 4.6 Conclusions Competition policy and sector-specific regulation have many limitations. Government interventions into market processes should therefore be applied restrictively. Sector-specific regulation generally infringes more on the freedoms of the regulated firm than antitrust policy. Furthermore, the likelihood of committing a Type-1 error is higher in sector-specific regulation when compared to general competition law.