# ARMONIA: A Unified Access and Metro Network Architecture
## 2 ARMONIA Architecture
### Description of ARMONIA Network  
In Figure 2, we present the general architecture of the unified and self-configured ARMONIA network. The data plane includes the metropolitan optical network, the mobile and the passive optical access (PON) networks. Access networks collect the traffic generated by users (fixed and mobile), homes, and businesses and forward it to the metropolitan network. From there, the traffic is transported to the respective destination either within the same metropolitan network or to another remote destination via the core network. The architecture at the data plane is complemented by the appropriate IP routers placed at the edges. These routers collect traffic from access networks, while there is at least one node that acts as a gateway to the network infrastructure. ARMONIA's goal is to transform existing network infrastructures through their effective integration into an overall control and management infrastructure (Figure 3). In this way, the metropolitan and access network segments will be dynamically and jointly operated. At the same time, their management can be centralized, using information from the actual state of the overall network infrastructure, and not only individual local information. The convergence and joint supervision of the access and metropolitan networks enables dynamic optimization of their respective resources. Hence, critical changes in the status of a segment can be detected immediately and appropriate actions can be simultaneously executed in any other network segment. Furthermore, the algorithms that analyze the monitoring information facilitate proactive network reconfiguration in order to offer consistent quality of service. Figure 1: ARMONIA’s closed control loop. To implement these functions, the architecture of ARMONIA includes the appropriate control and monitoring planes (Figure 3). The control plane is based on the principles of software defined networking (SDN). The provisioning manager governs the behavior of the network in response to the changing network conditions and in accordance with the applications' network requirements. It is responsible for the interaction of control, management and monitoring modules, namely (i) the ARMONIA SDN controller, (ii) the central telemetry handler, and (iii) the analytics and optimization algorithms. The ARMONIA SDN controller is responsible for network provisioning and re-configuration within the ARMONIA unified network infrastructure. The controller interfaces, primarily through the network configuration (NETCONF) protocol, with underlying network segments that utilize several networking technologies. ARMONIA supports two different deployment models: (i) the fully centralized model, where a central SDN controller operates on top of the unified network and (ii) the hierarchical model, where there is a set of domain/segment specific SDN controllers that cooperate with the ARMONIA controller. The hierarchical approach complies with the ITU G.7702 standard [16] and the IETF Abstraction and Control of Traffic Engineering Networks (ACTN) framework [17]. Both describe a hierarchy of SDN controllers that enable multi-domain coordination to support end-to-end services. Moreover, it is considered to be the most appropriate choice for production deployments since it ensures scalability, flexible control of the traffic, and dynamic configuration of the available network devices. Figure 3: ARMONIA unified control and monitoring. Figure 2: The ARMONIA network. Through the coordinated operation of the provisioning manager, the central telemetry handler, and the central SDN controller the ARMONIA network is able to perform the necessary actions to create new connections, to optimize existing ones, to configure monitoring devices, and to manage the recovery of a problematic connection (e.g., by rerouting or reconfiguring transmission parameters).