Connectivity Framework
2: Connectivity Framework
The layers above the network layer have evolved rapidly in the last decade and are not as widely recognized or understood. Therefore, the focus of this document is on the layers above the network layer, namely the transport and framework layers, as shown in Figure 2-2.
2.2 ARCHITECTURAL ROLE
The connectivity function in the IIRA supports exchange of data among endpoints in a system of interest. The information, for example, can be sensor updates, telemetry data, control commands, alarms, events, logs, status changes or configuration updates. Fundamentally, connectivity’ s role is to provide interoperable communications among endpoints to facilitate component integration.
Interoperability in communication can be achieved at various levels of abstraction, from custom integration to plug-and-play interfaces based on open standards. One common classification of interoperability is as follows( see Tolk, Wikipedia 1):
Technical interoperability is the ability to exchange information as bits and bytes( e. g. pencil scribbles), assuming that the information exchange infrastructure( e. g. pencil and paper) is established and the underlying networks and protocols are unambiguously defined.
Syntactic interoperability is the ability to exchange information in a common data structure( e. g. using words from a language), assuming that a common protocol to structure the data is used( e. g. the language’ s alphabet and rules of grammar) and the structure of the information exchange is unambiguously defined( e. g. whitespace, punctuation). Syntactic interoperability requires that technical interoperability be established.
Semantic interoperability is the ability to interpret the meaning of the exchanged data unambiguously as information in the appropriate context. However, the goal of the connectivity function is limited to provide syntactic interoperability between participating endpoints.
For IIoT systems, connectivity comprises two functional layers:
The connectivity transport layer provides the means of carrying data between endpoints. It provides technical interoperability between endpoints participating in a data exchange. This function maps to layer 4( transport) of the OSI model or the transport layer of the Internet model( see Table 2-1).
The connectivity framework layer facilitates how data is unambiguously structured and parsed by the endpoints. It provides the mechanisms to realize syntactic interoperability between endpoints. In this context,“ common data structure” refers to the structure or schema of the data being exchanged. Familiar examples include data structures in programming languages and schemas for databases. The connectivity framework function spans layers 5( session) through 7( application) of the OSI model or the application layer of the Internet Model( see Table 2-1).
1
See [ Tolk-2007 ], for overview [ WKPD-CI ]
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