PragmaticGeneralMulticast(PGM)isareliablemulticasttransportprotocolthatrunsoverabesteffortdatagramservice,suchasIPmulticast.PGMobtainsscalabilityviahierarchy,forwarderrorcorrection,NAK(negativeacknowledgement)elimination,andNAKsuppression.ItemploysanovelpollingschemeforNAKdelaytuningto