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Abstract-This paper describes the problematic of filter narrowing effect in the context of next generation elastic optical networks. First, three possible scenarios are introduced: the transition from actual fixed-grid to a flexi-grid network; the generic full flexi-grid network; and a proposal for filterless optical network. Next, we investigate different transmission techniques and evaluate the penalty introduced by the filtering effect when considering: Nyquist WDM, SSB DD-OFDM and symbol-rate variable DP-4QAM. Also, different approaches to compensate for the filter narrowing effect are discussed. Results show that the specific needs per each scenario can be fulfilled by the aforementioned technologies and techniques, or a combination of them, when balancing performance, network reach and cost.Index Terms-Networks, optical communications, elastic optical networks, flexi-grid, WSS. I. INTRODUCTIONThe future adoption of elastic optical network (EON), mainly fostered by the advent of next technologies (e.g., media, HDTV, 5G, Internet of Things, etc.) and backed by the considerable advances of transmission techniques in terms of flexibility and capacity, is heading to undertake new challenges and goals. In fact, when adopting the flexi-grid paradigm [1], optical channels with different bandwidth occupation can coexist within the same fiber. Some of these channels, denominated as super-channels, are wider in frequency and comprise multiple sub-channels transmitted

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Disaster-based failures can seriously disrupt any communication network, making its services unavailable. Such disruptions may be caused by natural disasters, technology-related failures, or malicious attacks, and they are observably increasing in number, intensity and scale. When network services that are a part of critical infrastructure become unavailable, commercial and/or societal problems are inevitable. The issue of limiting the impact of disaster-based failures needs to be urgently addressed due to the lack of suitable mechanisms deployed in the current networks.The COST CA15127 (RECODIS) Action will fill this gap by developing appropriate solutions to provide cost-efficient resilient communications in the presence of disaster-based disruptions considering both existing and emerging communication network architectures. It will be driven by researchers from academia and industry in strong cooperation with governmental bodies.In this paper, we highlight the objectives of RECODIS, its structure, as well as planned outcomes.

The problem of disaster resilience is of paramount importance in today's telecommunication networks. Here, this problem is tackled by considering 1+1 optical lightpath protection with maximally SRLG-disjoint paths and geodiversity in a transparent backbone network. Geodiversity was added to make the network more resilient to geographically correlated disasters. The aim is to estimate the increase of the path lengths (fibre lengths) and the increase in cost of the required transponders, with respect to simple link disjointness (no-SRLG nor geodiversity constraints) in a fully transparent optical network. The results obtained in a realistic test network show that SRLG-disjointness already ensures an acceptable geodiversity for the considered network.

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