Multiple networks may coexist as secondary users in white space spectrum or as equals in a spectrum commons.In this paper,we consider inter-network coexistence in license-exempt baads as a fully distributed dynamic channel allocation problem.Networks with cognitive features compete for channels following a polite spectrum etiquette without direct information exchange.Simulation results demonstrate that the distributed channel allocation following the proposed etiquette can quickly converge to a stable solution and achieve comparable performance comparing to existed dynamic channel allocation algorithms requiring explicit information exchange.