The scope of this deliverable was to clarify the architecture requirements of the system that is responsible for the co-optimization on cross-border capacity allocation (based on the methodology described in D8.1 and the market process presented in D8.2). More precisely, this report specifies the IT design and data management process for implementing the energy reserve optimization, providing the test set of order and market data for the OPTIM-CAP demonstration planning, interfaces and connection points for the dry-run operation at the end-user environment. In a nutshell, this deliverable consists of the following sections: In Section 1, the description of the overall business context was presented, i.e., the co-optimized market process and the relevant interactions between the actors. In Section 2, the overview of the system architecture was introduced, focusing on the data flow types and frequencies, and also the high-level environmental requirements. And in Section 3, the requirements regarding infrastructure and service level, the detailed description of platform decomposition, as well as the security and data management principles were presented.