Factory communications are a key element to achieve computer manufacturing integration. The problems are no longer caused by gaps in communication solutions, but rather by the heterogeneity of the network architectures. This paper surveys the different types of industrial communication profiles, with special emphasis given to those at the lower level of the automation hierarchy (field busses), where the problem of heterogeneity is much more acute. An internetworking device between a Manufacturing Automation Protocol network and a real time field bus network is discussed and proposed. The architecture of this device is based on a Manufacturing Message Specification server.