## 6 Conclusions  
As a result of the definition of a compulsory smart meter rollout by the EU parliament in 2009, the rollout of SMGWs in Germany started in February 2020. We showed that SMGWs are certified communication modules enabling a secure communication between meters and controllable devices on the one side, and external entities on the other side. According to the German rollout plan, standardized SMGWs will be broadly available in the near future and provide interfaces that can be used by EMS developers and providers. Even though SMGWs are currently specific to the German market, they could gain international importance, due to their distinct features, including the high security standards. On basis of this standardized infrastructure, we presented a proof of concept for the realization of DSM measures with the help of decentralized EMSs. Furthermore, we showed that the key functionality of SMGWs used for the implementation of such a value-added service is the provision of a transparent data tunnel for secure bidirectional communication. The first research question asks how DSM via a decentralized EMS can be implemented within the German SMGW infrastructure, and for the required design choices. To answer this question, we gave insights into technical details of the presented SMGW-based prototype. It implements a smart grid traffic light based DSM concept with variable electricity prices. We showed how the EMS handles charging processes and controls a charging station according to a cost-optimal charging strategy. The transparent data tunnel is used by the aEMP to send two kinds of information to the EMS: on a daily basis updated time-variable electricity prices, and in real time the current smart grid traffic light phase. Overall, the prototype comprises an SMGW, a GWA, an aEMP, and an automated EMS as CLS which manages and optimizes an EV charging station. Our implementation is based on a flexible hardware setup. It sets the foundation to evaluate the prototype with SMGWs from multiple manufacturers. We covered all of the three different communication scenarios, HKS3-5, that are available for establishing the transparent data tunnel and evaluated specific advantages and disadvantages. The source code for the EMS and the aEMP can be found in the supplementary materials (see note below). We argue that, for a DSMgr, HKS3 is generally the preferable communication scenario due to the highest degree of independence from the GWA. The second research question asks to which extent the SMGW infrastructure protects private data when integrating an EMS. To answer this question, the presented prototype was implemented in full compliance with not only technical but also security-related requirements. We used a certified GWA system and certificates from the SM-Test-PKI. Our prototype demonstrates that an aEMP can access sensitive data independent of tariff use cases if the user provides the consumer interface access to EMS. Therefore, we argue that the achieved level of privacy depends on the proper usage of the defined security mechanisms. This may in particular require bilateral contracts between the user of a CLS and the aEMP which cannot be technically enforced. The third research question asks where standardization hinders or supports the integration of EMS into the SMGW infrastructure. SMGWs provide standardized interfaces for communication with external parties and for access to meter data, hence minimizing costs for the operation of EMS. While all functionalities of intelligent metering systems aim to be interoperable, we showed that, at the implementation level, substantial differences between the SMGWs of the different manufacturers can be recognized. We point out that a major source of uncertainty for DSMgrs is that only one of the three HKS3-5 has to be implemented by the first generation of SMGWs. This can result in either higher development costs, or more complex market process for the provision of services.