Hands-on Demonstration of Open-Source Filterless-Aware Offline Planning and Analysis Tool for WDM Networks

We demonstrate an open-source filterless-aware multilayer WDM-network planning tool, that allows hands-on creation of mixed filterless/ed topologies and the application of built-in or user-developed algorithms and analysis tools for line engineering, spectrum and cost planning.

The Add/Drop modules can be realized with passive Mux/DeMux, or with WSSs (the latter being colorless). Finally, the architecture may be directionless or directioned. In the former case, each Add/Drop module is like a new degree, using WSSs and splitter/coupler depending on the architecture type. In the latter case, one Add/Drop module is attached to each degree with a hard-wired fiber connection. Parameters in Table I are used to compute the signal degradation effect of traversing each OADM. In filterless cases, the tool automatically characterizes the undesired propagation of the input signals, as waste spectrum occupation in out degrees. This information is used to validate the designs against wavelength clashing: no two lightpaths with overlapping spectrum can use the same fiber. Note that interestingly, the node model is able to capture the classical blocking situation [5] caused by resource contention in directionless Add/Drop modules: no two lightpaths can be added or dropped in the same add/drop module, with the same wavelength. The model incorporates enough information to compute four key signal performance parameters anywhere in the network: lightpath power, accumulated CD, PMD, and OSNR. Net2Plan algorithm plug-ins can also be used to calculate the nonlinear fiber transmission contribution to OSNR. Optical amplifiers with or without dispersion compensation are characterized with information describing how they modify these four aspects, and transponders include aspects like bandwidth, sensitivity, CD, PMD and OSNR tolerances. In all the cases, cost and energy consumption figures are included in the model, which will enable the application of network-wide analysis tools described below.

Filterless-aware algorithmic tools
Two key algorithms have been implemented specifically devoted to plan hybrid filterless/ed networks under the model described above. Firstly, an algorithm is available that permits solving the routing, spectrum and transponder type assignment, for a given set of available transponder types. The algorithm is filterless-aware, and accounts for the spectrum occupied by legitimate signals and by the waste spectrum that may be produced by the filterless nodes. The user can tune the algorithm to put emphasis in searching for a lower cost solution, or a solution with better spectrum efficiency. The algorithm is a variant of the multilayer IP over WDM algorithm developed in [9], and its code is publicly accessible within Net2Plan [7].
Secondly, we demonstrate an amplifier placement algorithm specific to networks where filterless nodes are restricted to degree 1 or 2, a sweet spot application for filterless architectures [9]. The algorithm first partitions the WDM plant into filterless components (i.e. topologies composed of sequence of fibers and filterless nodes). Then, for each component, pre-amplifiers and boosters are placed in the nodes minimizing its number according to a heuristic technique. The algorithm is suitable for metro networks, where minimizing the number of amplifiers is the target and the limiting factor is the optical power.
Altogether, the two algorithms compute the need for amplifiers, and the allocation of transponders, as well as route and spectrum allocation for arbitrary demands, which opens the door for strategic comparisons of different technological alternatives.

Filterless-aware analysis tools
Filterless capabilities added to Net2Plan NIW framework enable addressing some of the open questions related to this technology. These tools can easily analyze full network designs with potentially hundreds of nodes and fibers.  Route & Spectrum occupation analysis. The tool analyzes the spectrum occupation of the lightpaths, warning about clashes and/or internal blocking events, considering the propagation of the legitimate and waste signals in the fiber. In addition, it can identify lasing loops that can appear in filterless topologies (see Fig. 2 a) and c)). These are cycles of fibers and filterless nodes, that result in continuous propagation of waste signals, and that compromise the entire network performance (see Fig. 2 e)).   WDM line engineering analysis: Power, CD, PMD and OSNR are estimated using conventional models in all parts of the network. The user can explore this information in the graphical interface, and the tool automatically warns of e.g. unmet transponder tolerances or saturation situations at the optical amplifiers.  Cost & Energy consumption analysis: Based on the per-component information in the network model, the tool generates a report summarizing total CAPEX, as well as energy consumption information, suitable for technoeconomic analyses.

Innovation
We demonstrate and give hands-on access to novel filterless-aware planning resources like optical amplifier placement and RSA in flexi-grid networks. The analysis tools provided are unprecedented in the open-source community to gain insights in the filterless/ed networks WDM line engineering, spectrum efficiency, cost and energy consumption analysis. According to the Net2Plan NIW philosophy, an open and extensible software, new algorithms and reports can be developed and plugged in, extending, enhancing and customizing the built-in ones.
The filterless-aware planning and analysis innovations are of interest to e.g. decision making of network carriers to better evaluate filterless techno-economic impact. As an example, the demonstrated framework recently permitted us to identify filterless technologies as a sweet spot option when limiting its use to replace degree 1 and 2 OADMs in regional metro networks (e.g. 200 km of diameter) [9].

OFC relevance
Attendees will be able to download and run the software in our, or their laptops, create hybrid filterless/ed networks from scratch, and plan and analyze them in a hands-on experience, using solely the graphical user interface. No programming skills are needed.