## 1 Introduction  
Completely automated smart homes are on the way to becoming a well-established reality. The ever increasing number of smart objects in the smart home environment requires the definition of standardized and flexible protocols for commands and state information exchange, besides optimal strategies for processing a large number of commands. New technologies such as serverless computing and ad hoc communication protocols can be leveraged to manage a large fleet of smart objects, while also ensuring good accessibility and intuitive user interfaces. Serverless computing is an emerging cloud-computing paradigm that represents a promising development for many application fields, from micro- and web-services [1], to the the internet of things (IoT) [2, 3], edge computing [4] and artificial intelligence (AI) [5], or even for domain-specific scientific applications [6, 7]. Serverless computing operates at the crossing point of different models that have emerged alongside cloud computing, such as function as a service (FaaS) and pay-per-use models, and technologies such as event-driven programming, virtualization, and containerization [4]. Serverless computing comes with automated scalability and resource provisioning, meaning that resources assigned by the serverless platform scale depending on the number of functions that are running and the resource demand of each of those functions. These characteristics make serverless particularly appealing for applications that need to manage a large pool of users or, in the field of the internet of things and smart objects, a large number of devices [2]. The pioneering commercial platform for serverless computing was Lambda [8], developed by Amazon Web Services (AWS), the Amazon cloud platform. Lambda remains one of the most popular platforms for the development of serverless applications. A recent work by the authors of this paper [9] showed how AWS satisfies many key performance indicators in IoT applications, also compared to other competitors such as Microsoft Azure and Google cloud Platform, both of which now also offer serverless and FaaS services. Lambda also comes with extensive integration with Amazon Alexa [10], the voice assistant on Amazon Echo. Voice interfaces are seeing a wider use in different application fields, from voice assistants to home automation, as they constitute a more natural and intuitive interface to interact with smart objects and environments, as well as improving accessibility [11]. This paper proposes and experimentally evaluates a framework that represents a synergistic union of different cloud-computing and IoT-related technologies that can enable accessible and automated home environments. The framework is easy to replicate, is scalable, and is transparent to the underlying smart object or appliance that uses it due to the use of serverless technologies and a custom-defined command exchange protocol based on the message queue telemetry transport (MQTT) protocol. MQTT [12] is the main middleware service used in most cloud platforms for the IoT, therefore simplifying the interfacing of IoT devices and smart objects with the cloud. Compared to other protocols such as HTTP, which is also employed in many serverless solutions [3], MQTT messages have a small overhead that makes the protocol suitable for machine-to-machine applications. Furthermore, MQTT does not impose a format for its payload, making it extremely flexible [13], and the use of topics adds a further degree of freedom for the implementation of custom applications. As the introduction of new communication technologies in such applications requires careful evaluation in terms of the overall application latency, the aim of this paper is to evaluate the performance of a framework for smart home appliances equipped with narrowband IoT (NB-IoT) modules to send and receive messages to/from the cloud.