Understanding Smart Sensors - Nomads.usp

Communications for Smart Sensors 123OSI layersTypical task assignedControl networking requirements1ApplicationUser semanticsFile transferData objectsStandardized networking structures2PresentationData compressionUser data conversionNetworking structuresData interpretation3SessionSynchronizationDialog structureAuthenticationNetwork management4TransportReliable data transferEnd-to-end communicationEnd-to-end acknowledgmentDuplicate detection, automatic retries5NetworkRouting, logical addressingMAC-independent interfaceAddressing, unicast, multicast, broadcastRouters67Data-LinkPhysicalMedia access schemeError correction and framingPhysical interface definitionTransceiver interfaceMAC, collision avoidance/detectionFraming, data encodingCRC, error checkingPriorityMedia transceiversMAC = media access controlCRC = cyclic redundancy checkFigure 6.2 ISO’s Open Systems Interconnection (OSI) model.[4]. Researchers at Delft University of Technology have developed a serial communicationsprotocol [5]. The Integrated Smart Sensor (IS 2 ) bus is a mixedanalog/digital two-line serial bus interface. However, a protocol requires morethan definition and demonstration hardware. Accepted usage by a number ofmanufacturers ultimately determines the real standards that may, in fact,be de facto standards. University-developed protocols may achieve acceptancewith the adaptation of industrial users, but the process takes longer than utilizingexisting industry-sponsored standards. The focus of this chapter is standardsthat industry already supports. Table 6.2 lists the more commonstandards, including those developed by universities, manufacturers, and standardsorganizations.6.4 Automotive ProtocolsDue to its large volumes, the automotive segment has driven specifications,resulting in the actual implementation of protocols in several products. In automobiles,information from one sensor and/or data from one system can becommunicated with other systems using multiplex wiring to reduce thenumber of sensors and the amount of wire used in a vehicle. Two predominantprotocols have emerged as standards, but several other protocols exist for