code: @Override
      public void sendNackMessage(SIBUuid8 sourceMEUuid,
                                  SIBUuid12 destUuid,
                                  SIBUuid8 busUuid,
                                  long startTick,
                                  long endTick,
                                  int priority,
                                  Reliability reliability,
                                  SIBUuid12 stream)
                      throws SIResourceException
      {
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.entry(
                          tc,
                          "sendNackMessage",
                          new Object[] { new Long(startTick), new Long(endTick) });
  
          ControlNack nackMsg = createControlNackMessage();
  
          // As we are using the Guaranteed Header - set all the attributes as
          // well as the ones we want.
          SIMPUtils.setGuaranteedDeliveryProperties(nackMsg,
                                                    _messageProcessor.getMessagingEngineUuid(),
                                                    sourceMEUuid,
                                                    stream,
                                                    null,
                                                    destUuid,
                                                    ProtocolType.UNICASTOUTPUT,
                                                    GDConfig.PROTOCOL_VERSION);
  
          nackMsg.setPriority(priority);
          nackMsg.setReliability(reliability);
  
          nackMsg.setStartTick(startTick);
          nackMsg.setEndTick(endTick);
  
          //  Send Nack messages at original message priority +2
          sendToME(nackMsg, sourceMEUuid, busUuid, priority + 2);
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.exit(tc, "sendNackMessage ");
      }
docs: Sends a Nack message back to the originating ME