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Information transfer is an essential factor in automation systems. For reasons of practicability, the development of industrial communication networks focused on horizontal aspects, i.e., the provision of suitable automation networks on the various levels. Conversely, vertical integration has become a topic of interest only in the recent past and mostly concerns the interconnection of fieldbus systems and IP-based networks. This paper reviews gateway concepts and compares the applicability of the SNMP, LDAP, and OPC (OLE for process control) as higher-level access protocols based on a set of criteria that are relevant for fieldbus/IP gateways. It appears that after years of development, OPC has finally reached a promising state.