An overview of the Internet of Things (IoT) is given in this paper, with a focus on supporting technology, protocols, and application-specific challenges. The most recent advancements in RFID, smart sensors, communication technologies, and Internet protocols enable the Internet of Things. The fundamental idea is to create a new class of applications by having smart sensors work together directly without human intervention. The present Internet, mobile, and machine-to-machine (M2M) technology boom can be viewed as the beginning of the Internet of Things. The Internet of Things (IoT) is anticipated to connect physical things to enhance intelligent decision-making in the next years, bridging various technologies to open up new applications. This article begins by giving a broad overview of the IoT. Then, we provide a high-level review of a few technical aspects relating to the IoT enabling technologies, protocols, and applications. Our goal is to provide a more thorough summary of the most important protocols and application issues compared to other survey papers in the field so that researchers and application developers can quickly understand how the various protocols work together to deliver desired functionalities without having to read through RFCs and the standards specifications. We also give a brief review of some of the most important IoT challenges that have been discussed recently in the literature and a description of related research. We also investigate the connections between the IoT and other cutting-edge technologies, such as big data analytics, cloud computing, and fog computing. We also discuss how IoT services need to be more horizontally integrated. To show how the various protocols discussed in the paperwork together to deliver desired IoT services, we then present thorough service use-cases.