Objectives: The paper presents performance analysis of centralised and decentralised architecture of IoT sensor networks. Two most popular security mechanisms for Sensor Networks based on their energy consumption, which may lead to poor performance of the IoT system, are also evaluated. The Internet of Things (IoT) technology aims to improve easy access to the information needed using devices.Observations: It has been adopted by many time sensitive systems like self-driving car, automated traffic control system and so on. However, more study is required to understand performance level of possible IoT architectures over others. Results: This paper explains different IoT sensor network architectures and models decentralised Wireless Senor Networks (WSN) architecture. Simulation of these architectures and their popular security primitives are compared in terms of their performance. This study can be a great resource to develop an efficient IoT architecture and security framework with better performance.