Connectivity Framework 4: Connectivity Framework Layer
4.1.7 REQUEST-REPLY
A connectivity framework for IIoT should support the request-reply data exchange pattern. This data exchange pattern uses requestors that can initiate a service request to be fulfilled by endpoints in the replier role. An endpoint may operate in both a requestor and a replier role. This pattern is also called a pull or request-response data exchange pattern.
The request-reply data exchange pattern is useful when working with a sparse subset of large data— for example to query specific data objects or invoke specific services.
The request-reply data exchange pattern permits synchronous or asynchronous exchange of data between endpoints. In synchronous request-reply, a requestor waits for the replies before issuing the next request. In asynchronous request-reply, a requestor can have multiple outstanding requests and replies are processed as they are received.
4.1.8 DISCOVERY
To support more intelligent decisions, the discovery, authentication and access to services( including data exchanges) should be automated.
Connectivity frameworks provide mechanisms to discover the:
• publish-subscribe topics and the associated quality of service
• request-reply services and their associated quality of service,
• data types associated with the topics and services, and
• endpoints participating in a data exchange.
4.1.9 EXCEPTION HANDLING
A connectivity framework should also provide for exception handling, for example when there are disruptions in connectivity. This could happen because of:
• disconnected or intermittent links( at the lower layers),
• switching network interfaces( e. g. between wired and wireless links),
• changes in network configuration( e. g. cable replaced, network ports moved),
• data quality of service needs not met,
• remote endpoint or component failure, or
• non-responsive participants.
A connectivity framework should shield the data flows from the impact of such exceptions, and should provide a means of informing the applications when an exception cannot be automatically managed by the connectivity framework.
4.1.10 DATA QUALITY OF SERVICE( QOS)
IIoT data exchanges can have varying requirements for how the data is delivered. Those aspects are referred to as the data quality of service( QoS).
A connectivity framework should support these data exchange QoS categories. IIC: PUB: G5: V1.0: PB: 20170228- 30-