Xi protocol launched at OPC Foundation event

The purpose of this article is to provide answers regarding the Xi protocol (also known as Express Interface), which was recently presented by a set of companies in an event in the USA attended by SMAR representatives. But before that, let me introduce to you OPC DCOM and the timeline of its evolution to clarify what is the Xi.

Project background
The OPC Foundation was created in 1996 and in 1998 SMAR adopted the OPC standard for enabling data exchange of the SYSTEM302 Process Control System between specialized softwares responsible for providing the user with process data, as well as alarms and historic information.

Since then, it became evident that SMAR’s participation in the discussions at OPC Foundation could have a significative influence on the evolution of its SYSTEM302. That´s why in 2004 SMAR joined the OPC UA (United Architecture) study group, where through bimonthly meetings, in addition to teleconferences, we could follow in detail and help define this new architecture, which is based on platform independence, leaving aside the DCOM and the necessity of using the Windows operational system, the creation of a single addressing model for all the process data, in addition to alarms and history variables, enabling data description models, as the EDDL, the basis for the Fieldbus Foundation standard.

A new concept
This new concept was based on a service-oriented architecture, also known as Web Services, whose main feature is to cross through local network domains, without having to depend on IT staff to unblock firewall ports.

The UA architecture took five years to be defined and created a highly complex and generic standard that amounted to 700 pages of definition, divided in 13 parts, some with a conceptual phrasing, others defining the utilized services. However, this OPC UA generalization motivated some companies to work on a parallel development of the Xi protocol, to pursue something more focused on the migration of the existing DCOM platform that could run in a Microsoft environment and use the .NET framework. As SMAR mastered the technology and also shared some common interests, it helped define the Xi protocol and was instrumental for the current OPC Foundation interoperability show.

SMAR Brazil Delcio Prizon at the Xi Interoperability event in Orlando, Florida

An efficient and safe interface
The Xi is an easy to implement interface designed for efficient and safe communication through firewalls. It is based on MMS (Manufacturing Message Specification), .NET3.5 and WCF (Windows Communication Foundation) and was designed as a native communication interface between Microsoft clients and servers.

SMAR issued in September, 2009, the SMAR HSE Xi Proxy Server, which allows to preserve the entire existing DCOM platform with a minimum effort and also gain the Xi connections for Web Services communication. With this proxy, it is already possible for Xi supervisory systems to access all the supervision variables present in an HSE (High Speed Ethernet) network. This ensures that in new and existing plants, provided that the client already has the Xi protocol, the data are available for the corporate areas easily, inclusive by the use of HTTP as communication protocol.

As Web Services, the server is accessed not only through the serving machine IP, but also through an URL. The connections can be established with client and server on the same machine by the WCF Named Pipe bindings (netPipe) and, if necessary, connecting internet network environments through HTTP.

Besides SMAR, the initial participants on the Xi protocol definition are: Advosol, Emerson, Honneywell, Iconics, Indusoft, Matrkon, Mobiform, Mynah Technologies, OSIsoft.

Ernani Veríssimo (SMAR Houston) and Delcio Prizon at the Xi Interoperability event in Orlando, Florida