code: public SubscriptionIndex getSubscriptionIndex()
      {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
          {
              SibTr.entry(tc, "getSubscriptionIndex");
              SibTr.exit(tc, "getSubscriptionIndex", _subscriptionIndex);
          }
          return _subscriptionIndex;
      }
docs: Retrieve the subscription index for this destination.
  
  @return SubscriptionIndex.