code: public void sendRequest() throws SipException {
          //hack to add this tx as cancelable, in case someone use x send, instead of dialog.send(ctx);
          validateWrappedTransaction();
          final String method = this.wrappedTransaction.getRequest().getMethod();
          final DialogWrapper dw = getDialogWrapper();
          if ((method.equals(Request.INVITE) || method.equals(Request.SUBSCRIBE)) && dw != null) {
              dw.lastCancelableTransactionId = this.activityHandle;
          }
          if (tracer.isInfoEnabled()) {
              tracer.info(toString() + " sending request:\n" + getRequest());
          }
          wrappedTransaction.sendRequest();
      }
docs: /*
  (non-Javadoc)
  @see javax.sip.ClientTransaction#sendRequest()