We extend the theory of advertising as a quality signal, using a model where an entrant can choose to advertise by comparing its product to that of an established incumbent. Comparative advertising, comparing quality of one’s own product to that of a rival’s, empowers the latter to file for...

Central features of today's electronic communications markets are complementarities between the different layers of the value chain, substitutability between some applications, network effects in the provision of content and services, two-sided business models that partly involve indirect...