This paper presents the design aspects of a generic multi-service cloud-based IoT operational platform EMULSION, which is a representative of the new horizontal type, next-generation, IoT platforms that come as a replacement of the existing vertical type platforms. The architectural design and main characteristics of the platform are presented and its multi-tiered structure is explained. Utilizing this EMULSION platform, two pilot platform-demonstration IoT systems are being designed. These along with their performance tests and demonstrations will be reported on in a future paper.