Applicability of Internet protocols for fieldbus access

Gateways between IP-based networks and fieldbus systems often create the impression of providing a unique, standardised remote access to automation systems. At second sight, however, it becomes apparent that there are several possibilities on the LAN side with individual strengths and shortcomings. This paper reviews typical functions expected from a fieldbus gateway and investigates the properties of SNMP, LDAP, SQL, HTTP and a specially designed proprietary protocol (IGUANA) with respect to their appropriateness for remote access. Particular emphasis is laid on the restriction these protocols impose on the way the data inside the gateway are structured. We find that none of these approaches fully satisfies all requirements.