Forapairofnodess,tinanundirectedgraphG=(V,A)andagivenlevelUofallowabledelay,wewouldliketomodifythenetworkbynode-basedoredge-basedupgradingstrategiestomakethedelaybetweensandtnotgreaterthanU.Inthispaper,wepresentsomeNP-hardresultsforthedelayimprovementproblems.