Received: 2 March 2019 Revised: 3 August 2019 Accepted: 9 August 2019 DOI: 10.1002/ett.3742 SPECIAL ISSUE ARTICLE Quality of service in IoT protocol as designs and its verification in PVS Muhammad Saqib Nawaz 1 Meng Sun 1 Basit Shahzad 2 M. Ikram Ullah Lali 3 Tariq Umer 4 Shaohua Wan 5 1 School of Mathematical Sciences, Peking University, Beijing, China 2 Faculty of Engineering and Computer Science, National University of Modern Languages, Islamabad, Pakistan 3 Department of Computer Science, Faculty of Computing and Information Technology, University of Gujrat, Gujrat, Pakistan 4 Department of Computer Science, COMSATS University Islamabad, Wah Campus, Wah Cantonment, Pakistan 5 School of Information and Safety Engineering, Zhongnan University of Economics and Law, Wuhan, China Correspondence Shaohua Wan, School of Information and Safety Engineering, Zhongnan University of Economics and Law, Wuhan 430073, China. Email: shaohua.wan@ieee.org Funding information National Natural Science Foundation of China, Grant/Award Number: 61772038, 61532019, and 61272160; Guandong Science and Technology Department, Grant/Award Number: 2018B010107004 Abstract Reliable data transmission during communication in Internet of things (IoT)–based systems has gained much interest in last few years due to the cur- rent growth and huge investment in such systems. Message Queue Telemetry Transport (MQTT) is an open publish/subscribe–based messaging protocol that is widely used for device communication in IoT. For data transmission between devices, different levels of quality of service (QoS) are used in MQTT. In this paper, we provide a formal model for MQTT protocol under the Unifying Theo- ries of Programming (UTP) semantic framework, where QoS levels in MQTT are modeled as designs in UTP. Refinement and equivalence relations between QoS levels can be established naturally via implication between predicates. Moreover, Prototype Verification System (PVS) is used to encode the UTP design models and some important properties as well as the refinement relation between QoS levels is proved with the PVS proof assistant. 1 INTRODUCTION In 1999, the term Internet of things (IoT) was first introduced by Ashton. 1 The basic definition of IoT has evolved with time, and now, IoT provides connectivity for almost all physical devices that have some storage and computational power. Such connectivity enabled these devices to collaborate and exchange data at any time, from anywhere, and in any form. Moreover, recent development and evolution in information technology and the increasing popularity of mobile commu- nication have made it possible to directly integrate the physical world into computer-based systems through IoT. Such integration offers economic benefits, improves efficiency, and reduces human intervention in the network. It is predicted by Nordrum 2 that there will be around 30 billion IoT devices by 2020 and the net worth of IoT will be approximately 7.1 trillion dollars. 3-8 Trans Emerging Tel Tech. 2019;e3742. wileyonlinelibrary.com/journal/ett © 2019 John Wiley & Sons, Ltd. 1 of 15 https://doi.org/10.1002/ett.3742