User's Manual

GuardianManual0015006000Rev0 18|Page
2.2.2 POINTTOMULTIPOINT
APointtoMultipointnetworkisacommonnetworktypeusedinSCADAorotherpollingsystems.Thesingle
pollingmasterstationcommunicateswithanynumberofremotesandcontrolsthenetworkbyissuingpollsand
waitingforremoteresponses.IndividualPLC/RTUremotesmanageaddressingandrespondwhentheirindividual
addresses
arequeried.PLC/RTUunitaddressesaremaintainedinascanningliststoredinthehostprogramor
masterterminaldeviceattheSCADAhostsite.Communicationsequipmentistransparentanddoesnotinteract
withspecificremotes;alldataiscoupledtothehostonasingledataline(sucha
networkiscommonlyusedwith
synchronousradiomodemsandasynchronousradiomodems).
Figure2.2PointtoMultipointNetwork
2.2.3 MULTIPLEPOINTTOPOINT
AmultiplepointtopointissimilartothepointtomultipointsystemexcepttheSCADAhosthasmultipleserial
portsthataredirectedtodifferentgeographicareasintheSCADAsystem.
2.2.4 PEERTOPEER
APeertoPeernetworkisgenerallyusedfordevicetodevicecommunicationsamonganumberofstations.This
networkrequiresfulladdressingcapabilityonthepartofthedataequipment(DTE).Ifthedistancesinvolvedfor
anylinkorlinksaretoogreatforasingleradiohop,theycan
beextendedbymeansofrepeaterswithoutaffecting
thebasicnetworkdesign.
2.2.5 STOREANDFORWARD
StoreandForwardisacommontechniquewhereadatatransmissionissentfromonedevicetoareceivingdevice
butfirstpassesthrougharelayingdevice.ThedeviceistypicallyanRTUorPLCusedbythemessageserviceto
storethereceivedmessagethenittransmitsthemessageto
theintendedrecipient.