public function request($requestClientId, Array $payload, Closure $handler)
	{
		// generate a new requestId
		$requestId = $this->uuid();

		// store the handler
		$this->handlers[static::MESSAGE_TYPE_REPLY][$requestId] = $handler;

		$m = $this->bareMessage(static::MESSAGE_TYPE_REQUEST);
		$m->RequestClientId = $requestClientId;
		$m->RequestId = $requestId;
		$m->Payload = $payload;

		$this->send($m);
	}