
56-6 Industrial Communication Systems
Model (DCOM) [RGR97] or the transport layer of the.NET specication. However, due to complex-
ity, management eort, and security reasons, a much simpler solution was requested. e Simple
Object Access Protocol (SOAP) [DBX00] was dened to overcome the limitations and to provide a
“rewall-friendly” way of invoking functions. SOAP is a protocol that can be bound to several under-
lying transport layers, including HTTP and SMTP. e functions calls, the responses, and possible
error messages are serialized in coded format using eXtended Markup Language (XML) and are then
embedded into the transport protoco