to the nms as per itu t g 798 in general only the alarm with higher hierarchy is issued to the nms for example i if a defect is detected at ops layer the alarm for that defect is issued but all the other possible defects detected at otuk oduk layers are not issued ii if no defect is detected at ops layer but a defect is detected at otuk layer the alarm for that defect is issued but all the other possible defects detected at oduk layer are not issued a modification of the operation of the alarm correlation unit 210 according to an embodiment of the invention compared to g 798 is that if the defect detected at otuk layer is otuk ais no otuk ais alarm is issued for that defect and alarms for all the other possible defects detected at the oduk layer are not issued based on the defects detected by units 206 a 206 b 206 c the consequent action management unit 211 issues an instruction 213 to a consequent action insertion unit 214 to inject an oduk ais signal in an oduk frame as per itu t g 798 recommendation the otuk ais is a pn 11 sequence that fills all of the otu frame including the oh and the otu payload as shown in fig8 when the odu cross connect 20 detects the otuk ais at unit 205 then consequent.