Advanced Optical Transport Network featuring WDM/SDM
The optical transport network, located at the lowest level of the ADRENALINE infrastructure, is a hybrid fixed/flexi-grid DWDM core network with whitebox ROADM/OXC nodes and software-defined optical transmission (SDOT) technologies, including sliceable-bandwidth variable transceivers (S-BVTs) and programmable optical systems (further detailed later on in the EOS platform). The optical transport network network is shown schematically in next figure, including, macroscopically, the core part and the access part. It is worth noting that the infrastructure can also suitably feature the metro/aggregation network segment.
The optical core network includes a photonic mesh network with 4 nodes (2 ROADMs and 2 OXCs) and 5 bidirectional DWDM amplified optical links of up to 150 km (610 km of G.652 and G.655 optical fiber deployed in total). It combines links at DWDM 100 GHz channel spacing, links at 50 GHz channel spacing and links using a flexi-grid channel spacing using commercially available WSS. Let us note that the infrastructure is being progressively migrated to a have a complete set of flexi-grid links. However, it is expected that hybrid deployments combining fixed and flexi-grid links will be common in production newtorks (while operators actually perform such migrations) so the actual state allows us to address the challenges in deploying services in such heterogeneous optical networks, including backwards compatibility with already deployed systems and channel grids, limitations in optical spectrum management, etc.
The optical access network has been recently added to support/emulate new fronthaul networks (see next figure). Let us mention that Digitized radio over fibre (DRoF) is a popular fronthaul technology that is being deployed worldwide for giving service to radio access networks (RANs). This allows centralization with clear advantages in the reduction of CAPEX/OPEX costs in the outside plant, as remote radio units (RRUs) are expected to have smaller installation footprint and energy consumption than a classic base station.
This allows centralization with clear advantages in the reduction of CAPEX/OPEX costs in the outside plant, as remote radio units (RRUs) are expected to have smaller installation footprint and energy consumption than a classic base station. However, with the increasing capacity demand of 5G, new radio (5G-NR) waveforms and processing are expected in an environment where small cells are massively deployed at high density. This means that in order to maintain a certain scalability and meeting its stringent latency requirements, it is required to adapt DRoF to a new paradigm implying an upgrade of the network fibre plant to include space division multiplexing (SDM) by deploying multicore fibres (MCFs). This implies finding the suitable combination of wavelength division multiplexing (WDM) and SDM technologies to substantially increasing the total capacity of a RAN. Indeed, this suitable combination of WDM/SDM technologies also enables targeting ultra-high capacity metro/aggregation networks. In view of this, an additional node (Node-5) has been recently added, connected to Node-4 using a 19-core 25Km MCF. With 2 SDM Fan-in/Fan-out deployed at nodes 4 and 5, access nodes (Node-6 and Node-7) can be connected to the optical core. This can be used to emulate multiple scenarios as shown in next figure.
Finally, S-BVTs implement flexible programmable (SDN-enabled) optical transmission systems, based on modular transceiver architectures and suitable photonic technologies. Key advanced functionalities can be enabled and tested to fulfill the dynamic requirements and flexibility challenges of future optical networks. This includes spectral manipulation and rate/distance adaptability for optimal spectrum/resource usage, as each transceiver module is capable to generate a multi-format variable rate/distance data flow (slice). From the control plane perspective, the optical core network is based on the SDN paradigm, as detailed later.