# ARMONIA: A Unified Access and Metro Network Architecture
## 1 Introduction  
Internet traffic is expected to grow steadily at a rate of about 25% per year by 2022 [1]. This increase is the result of the new applications' demands such as cloud computing, Internet of Things (IoT), and fifth generation (5G) networks. Mobile networks are expected to contribute the largest share (50%) of this projected traffic increase [2] pushing technological changes. A significant amount of this traffic will remain 'local' in that it will not be transmitted to remote network locations. Moreover, due to the explosion of traffic data generation coming from many new applications, the access and metropolitan networks will be stressed significantly. In such an environment, there is a need for dynamic and flexible operation and cooperation of these network domains. Traditionally, the metro, access and mobile networks operate statically and separately. The optical paths (lightpaths) of metropolitan and core optical networks transfer traffic from the IP routers located on their edges, offering connectivity to mobile and access networks. During the lifetime of a lightpath,its quality of transmission (QoT) decreases for a number of reasons: ageing of equipment, increased interference due to new connections, equipment degradation/failures, etc. To this end, optical paths are installed with unfavorable network conditions (\"high margins\") in order to operate statically and safely for many years during which real conditions will deteriorate [3]. Also, due to the static operation of the optical networks, network replanning is needed in order to serve the growing capacity requirements. This includes installation of new equipment and re-configuration of existing devices [4], resulting in increased capital (CAPEX) and operating costs (OPEX). Overall, the static network operation, the overestimation of the requirements of the optical physical layer, as well as the isolated operation of the different parts of the network, are extremely inefficient. Significant benefits, in terms of capacity and cost, can result from the reduction of \"margins\", the dynamic operation of optical networks [5; 6] and the co-design and co-operation of the different network parts [4; 7]. Innovative network technologies such as software defined networks (SDN) and network function virtualization (NFV) can enhance efficiency and reduce CAPEX and OPEX costs. SDN is a control framework that provides programmability of network functions and protocols by decoupling the data plane and the control plane. With SDN, network intelligence and state information are logically centralized within controllers. SDN is expected to play a crucial role in the design of future wired and wireless networks, providing dynamic capacity allocation, on demand adaptation of connections, and rerouting of traffic according to network and application characteristics. SDN-based advances have been presented for the joint orchestration of different network and computing domains. The authors in [8] present an OpenFlow based SDN unified control plane for the integration of heterogeneous state-of-the-art optical and packet transport domains. In the same context, the authors in [9] apply hierarchical SDN controllers for the orchestration of heterogeneous (Ethernet, OpenFlow/GMPLS) network domains. Multi-domain orchestration was also presented in other works, with orchestrators able to jointly manage cloud and networking resources, operating over multi-layer and multi-domain network controllers [10]. In [11], hybrid electrical-optical switching and elastic optical network interconnection technologies are put under a common orchestration framework, providing intra-datacenter and inter-datacenter dedicated capacity in real time. In [12], an SDN platform is developed supporting reconfigurability over converged fiber-wireless network resources. At the same time, NFV enables the virtualization of the functions of mobile networks that are traditionally implemented with expensive and specialized (proprietary) equipment.