# Emulating Software-Defined Disaggregated Optical Networks in a Containerized Framework
## 1 Introduction
### State of The Art  
The literature has a growing number of works focused on SDN DON and optical network emulation. However, studies that consider both topics from the application layer to the data plane are scarce. One interesting starting point to link SDN and DON is to put the light on the SDN controller. Some works like [13; 20; 21], embrace this approach, first by proposing a model-driven design of a SDN controller and, second, upgrading the functionalities of the SDN controller ONOS to support disaggregated optical networks. Such new capabilities include YANG models compatible with NETCONF-based SBIs that communicate with the optical devices. In [22], this idea is expanded to not only be applied to the controller but also to a high level of abstraction that comprises the control plane in multi-domain disaggregated optical networks. Furthermore, a monitoring and data analytics architecture is proposed in [23] to monitor optical disaggregation. On the other hand, several studies focus on the data plane, precisely on modelling devices in the context of DON. For instance, YANG models and their implementation, via agents, of (SDN-enabled) sliceable bandwidth/bitrate variable transceivers (S-BVTs) have been presented for partially [24] and fully disaggregated optical networks [25]. One of the most important actors in optical networks is the reconfigurable optical add/drop multiplexer (ROADM) that implements the add and drop capabilities in optical nodes. They are addressed within the DON scope in [26; 27]. Additionally, focusing on the data plane, [28] reports a gap analysis on physical-layer parameters of YANG models available in the OpenConfig, OpenROADM and OpenDevice projects for estimating the quality of transmission (QoT). In addition, this work is complemented by a proof of concept focusing on the reception of the relevant parameters from an OpenConfig muxponder in the application layer for planning purposes. Relevant in the context of data-plane initiatives, it is worthwhile mentioning GNPY [29]: the open-source planning tool for the data plane in optical networks. GNPY is based on the Gaussian Noise (GN) model [30], and reported validation results in large-scale optical transmission testbeds [31]. In particular, [31] reports the GNPY validation in a mixed-fibre test-bed at Microsoft labs in which transponders of eight different manufacturers operated in the C-band reaching a propagation distance of 1945 km. Relevantly, GNPY has also been considered as an assistance tool for the computation of impairments in optical-layer paths on top of SDN controllers [32]. Nonetheless, these efforts are scarce in the literature because optical-layer awareness is commonly considered as stand-alone planning tools separated from operational aspects addressed by SDN controllers. The next stage towards emulating a DON environment is device virtualisation that exploits the benefits provided by YANG models of devices, which is also explored in the community. A network virtualisation architecture for open (partially) disaggregated network uses the concept of device hypervisor in virtual networks by using OpenROADM data models [33]. Furthermore, another common approach for adding virtualization to DON-based devices is to implement their related agent in a virtual machine (VM)/container that can emulate a realistic behaviour of the optical device. This eases the instantiation and the management of the virtual entities with a computer or a server. Those VMs/containers must be configured to enable the SBI communication implementing the interaction with the SDN controller [13]. Finally, it is also worthwhile mentioning comparable initiatives to our proposal such as the software-defined packet-optical network emulator [34], which is based on an optical extension of the popular packed-oriented network emulator Mininet [35]. Relevantly, ref. [34] proposes a software suite capable of emulating optical-layer QoT performances such as OSNR, gOSNR and BER, and report its impact to the SDN controller.