Mediators stand as a core architectural paradigm for today's and future systems that increasingly need be connected. The mediator concept has been used to cope with many heterogeneity dimensions spanning: terminology, representation format, transfer protocols, functionality, and application-layer protocols. Still, a key challenge for today's systems architectures is to embed the necessary support for automated mediation, i.e., the connector concept needs to evolve towards the one of mediating connectors. In this paper, we concentrate on the issue of enabling automated protocol mediation. Building upon tremendous research work in the area over the past few years we introduce a formalization of mediating connectors. The proposed formalization paves the way for automated reasoning about protocol matching and mapping, and thus for the dynamic synthesis of mediating connectors to enable eternal networked systems, which we investigate as part of the CONNECT European project.