We present a specification for a new, localized group membership service that maintains the membership status of adjacent nodes — called neighbors — in a mobile distributed system. The service builds on top of a neighborhood service which employs a simple heartbeat mechanism to discover and track neighbors in the mobile network. Both services assume unreliable communication as found in the wireless environment. No knowledge of the network topology is presumed.

We impose a deadline for installing views of the membership to force timely deciding protocols. We give a simple implementation of the neighborhood and the group membership service. If the deadline of view installations is at least the heartbeat rate, we can prove the correctness of our suggested implementation. An application in mobile ad hoc networking exemplifies potential areas of deployment for a localized group membership service.