Redundancy Design Solutions in Industrial Routers and Cellular Communication Devices Table of Contents 1. Introduction: Why Do Cellular Communication Devices Need "Redundancy"? 2. Fundamental Concepts 2.1 What is Single Module Single SIM 2.2 What is Single Module Dual SIM (Dual SIM Single Module) 2.3 What is Dual Module (Dual Module / Dual Modem) 3. Detailed Working Principles of Single Module Dual SIM 3.1 SIM Card Switching Mechanism 3.2 Switching Latency Analysis 3.3 Techn