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 -