## 5 Conclusions  
A set of architectural principles and key enablers for the horizontal architecture have been specified in this work in order to contribute towards solving the grand challenges related to complexity and \"vertical silos\" limiting the M2M market scale and interoperability. A selected set of key enablers called as autonomic M2M manager, M2M service capabilities, M2M messaging system, M2M gateways towards energy constrained M2M asset devices and creation of trust to enable end-to-end  
\begin{table}
\begin{tabular}{c c} \hline \hline
**GEs of Fi-Ware architecture** & **Comparison with provided architectural principles** \\ \hline Cloud hosting & It is seen that the provided architectural principles are agnostic of the cloud hosting, in the sense that it is expected that resulting information and service layer could be executed as the platform within a cloud. However, this kind of hosting has not yet been evaluated. \\ \hline Data/context management & It is seen the autonomic M2M manager could apply GEs of data/context management as means for working with the information \& knowledge bases. However, it is here estimated that this area is still open area for research, because of heterogeneous M2M application domains \\ \hline Internet of Things (IoT) services & It is seen that the ETSI M2M service capability layer is quite comparable solution with the generic enablers of Fi-ware related to services enablement. However, we rely in our work more on the open standards based solutions than open API based solutions provided by specific companies. \\ \hline Application/services ecosystem and delivery framework & It is seen that the provided architectural principles are agnostic of the application/services ecosystem and delivery framework, in the sense that it is expected that developed service solutions could be delivered via any delivery framework. However, this kind of application delivery has not yet been evaluated. \\ \hline Security & Our contribution to security part is related to enabling end to end security and trust for the M2M system. This is quite limited compared with the Fi-Ware generic enablers for security, and it isn’t possible to compare properly the approaches for end to end security and creation of trust when writing this publication. It is here estimated that this area is still open for research, because of multiple views into the ownership of M2M devices and information, and the related business aspects. \\ \hline Interface to Networks and Devices & Our contribution relies on the XMPP based M2M communication overlay, which hides the heterogeneity of networks to the services. The relationship of it with the Fi-Ware I2 ND GEs is not clear, and a potential overlapping with ETSI M2M service capability layer has been detected. However, any proper evaluation with Fi-Ware I2 ND GEs has not yet been done. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison.  
security for M2M applications have been developed. The developed key enablers have been evaluated separately in different scenarios dealing with smart metering, car sharing and electric bike experiments.  
The evaluation results show that the provided architectural principles, and developed key enablers establish a solid ground for future research and seem to enable communication between objects and applications, which are not initially been designed to communicate together.. The aim as the next step in this research is to create a combined experimental system in order to evaluate the system interoperability and performance in a more detailed manner. In addition, it is seen that especially the areas related to M2M information management, M2M security and interaction with constrained embedded M2M devices are open areas for future research.