code: private void startNegotiators() {
  
          for (ContentNegotiator contentNegotiator : contentNegotiators) {
              TransportNegotiator transNeg = contentNegotiator.getTransportNegotiator();
              transNeg.start();
          }
      }
docs: When we initiate a session we need to start a bunch of negotiators right after we receive the result
  stanza for our session-initiate.  This is where we start them.