## 2 Data Network Infrastructure for HSS
#### DNIHSS Communication Components  
The DNIHSS services are built in blocks having restrictive services, actions, and tasks [36, 37]. This block modularity and restriction of responsibility offers the following advantages:  
* Independence of software solution implementation: the blocks can be implemented with different technology and software solutions;
* Increased security of the architecture by simplification of concerns: the reduction of responsibilities of each block confines the impact of the action of hackers in case of a compromised module. Usages of different technology solutions in the individual blocks increase the difficulty of hacking activity;
* Responsibility division: the assignment of well-defined responsibilities to the blocks allows a simplified substitution of them by other ones with different technology and implementation solutions. The well-defined responsibility facilitates the security and activity supervision, detecting malicious activity faster;
* Redundancy existence: the blocks can be implemented alongside other blocks with the same responsibilities to add in redundancy and performance. This modularity increases the resilience of the architecture to failures and attacks. Figure 4: Temporary installation of a DNIHSS using ATAA deployed as needed. Figure 3: Permanent Installation of a DNIHSS using ATAA over the sea. The different HSS served by the DNIHSS have their own components and local data networks infrastructure distributed in the geographical area, interconnecting sensor, actuators, and local services to an HSS module. This HSS module functions as a gateway between the HSS service local components and the DNIHSS. Over the DNIHSS, these HSS modules communicate to its corresponding HSS cloud managing services and to other modules from the same HSS. All the communication between the DNIHSS services, its actions, interactions, and tasks are registered in Blockchains managed by independent Blockchain services. It guarantees the transactions' registration immutability, security, transparency, and auditability, establishing trust and transparency over its transactions, actions and operations. As long as it is contracted between two different HSS managing services and authorized by the NMS, one HSS module can communicate to another module from a different HSS. This enables the sharing of resources between two different service modules, without compromising security and service independence. These communications are always made over the DNIHSS and managed by the NMS. An HSS module cannot communicate to another HSS managing service except its own. The medium for the data exchange between the different blocks is call commands [28]. The commands encapsulate the type of the needed interaction. The main interaction activities can be characterized as status request, action order, and data transport [28]. An HSS module data exchange command frame [28] is illustrated in Figure 5.  
The data exchange command frames are delivered and received by the DNIB. The DNIB are the point of connection for the heterogeneous services modules to the DNIHSS. The DNIB are responsible for receiving the encrypted data from the HSS modules, creating the data exchange command frame, and delivering the command to its destination. The majority of the HSS modules data exchange is delivered in asynchronous data exchange command frames, but when necessary, the DNIB in collaboration to other DNIB can create temporary Virtual Private Networks (VPN) between the HSS modules and their corresponding cloud services. A representation of the DNIB within the DNIHSS is presented in Figure 6. Each HSS module is connected to its components over a local private data network. The HSS modules are connected to the DNIB by a Block Interface (DNIBI). The DNIBI does not have the knowledge about the business processes or data structure of the DNIB or the HSS module. Its relation is restricted to previously contracted command types. The restricted command types delivered by a certain DNIB are granted and managed by the NMS.