Understanding Smart Sensors - Nomads.usp

278 Understanding Smart SensorsNetworkhardwareNetworkprotocolI/O porthardwareTransducersoftwareNetworkApplicationsoftwareTransducer(sensorsandactuators)Network protocollogical interfacespecificationTransducerlogical interfacespecificationTransducerhardwareinterfacespecification(e.g., IEEE 1451.2)Figure 12.4 Networked smart transducer model. (After: [2].)12.3.2 Network Communication ModelsThe IEEE 1451.1 standard provides two models for network communicationbetween objects. The point-to-point client/server model is tightly coupled forone-to-one communications. The publish-subscribe model is loosely coupledfor one-to-many and many-to-many communications. Network software suppliersare expected to provide code libraries that contain routines for the callsbetween the IEEE 1451.1 communication operations and the network [2].Figure 12.5 shows the client-server used in IEEE 1451.1 [2]. The modelis supported by two complementary application-level operations:• Execute on client-side client-port objects;• Perform on all network-visible server-side objects.The execute and perform operations work together to provide a remoteobject-operation-invocation-stylemessaging service [2].The publish-subscribe model in IEEE 1451.1 is shown in Figure 12.6 [2].The model provides a means for loosely coupled communications between