code: public void start() throws InterruptedException {
      logger.debug("Staring client TLSTransportClient {} ", socketDescription);
      if (isConnected()) {
        logger.debug("Already connected TLSTransportClient {} ", socketDescription);
        return;
      }
  
      workerGroup = new NioEventLoopGroup();
      Bootstrap bootstrap = new Bootstrap();
      bootstrap.group(workerGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel channel) throws Exception {
          ChannelPipeline pipeline = channel.pipeline();
          pipeline.addLast("decoder", new DiameterMessageDecoder(parentConnection, parser));
          pipeline.addLast("msgHandler", new DiameterMessageHandler(parentConnection, false));
          pipeline.addLast("startTlsInitiator", new StartTlsInitiator(config, TLSTransportClient.this));
          pipeline.addLast("encoder", new DiameterMessageEncoder(parser));
          pipeline.addLast("inbandWriter", new InbandSecurityHandler());
        }
      });
  
      this.channel = bootstrap.remoteAddress(destAddress).connect().sync().channel();
  
      parentConnection.onConnected();
  
      logger.debug("Started TLS Transport on Socket {}", socketDescription);
    }
docs: only client side