code: @Override
      public void sendNackMessage(
                                  SIBUuid8 upstream,
                                  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(priority, reliability, stream);
  
          nackMsg.setStartTick(startTick);
          nackMsg.setEndTick(endTick);
  
          if (upstream == null)
          {
              upstream = _originStreamMap.get(stream);
          }
  
          // Send this to MPIO
          // Send Nack messages at message priority +2
          _mpio.sendToMe(
                         upstream,
                         priority + 2,
                         nackMsg);
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.exit(tc, "sendNackMessage ");
      }
docs: Called by one of our input stream data structures when we don't have
  any info for a tick and need to nack upstream.
  
  @param startTick
  @param endTick