code: @Override
      public void sendAckMessage(
                                 SIBUuid8 upstream,
                                 SIBUuid12 destUuid,
                                 SIBUuid8 busUuid,
                                 long ackPrefix,
                                 int priority,
                                 Reliability reliability,
                                 SIBUuid12 stream,
                                 boolean consolidate) throws SIResourceException, SIErrorException
      {
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.entry(tc, "sendAckMessage", new Long(ackPrefix));
  
          if (upstream == null)
          {
              upstream = _originStreamMap.get(stream);
          }
  
          ControlAck ackMsg = createControlAckMessage(priority, reliability, stream);
  
          ackMsg.setAckPrefix(ackPrefix);
  
          if ((consolidate) &&
              (_internalInputStreamManager.hasStream(stream, priority, reliability)))
          {
              try
              {
                  processAck(ackMsg);
              } catch (SIResourceException e)
              {
                  // FFDC
                  FFDCFilter.processException(
                                              e,
                                              "com.ibm.ws.sib.processor.impl.PubSubInputHandler.sendAckMessage",
                                              "1:600:1.329.1.1",
                                              this);
              }
          }
          else
          {
              // Send this to MPIO
              // Send Ack messages at the priority of the original message +1
              _mpio.sendToMe(
                             upstream,
                             priority + 1,
                             ackMsg);
  
          }
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.exit(tc, "sendAckMessage");
      }
docs: All of our matching local subscribers and/or output handlers have acked the
  message so tell the upstream sender.
  
  @param ackPrefix
  @param msgSource
  @param priority
  @param reliability
  @throws SIResourceException