# Time Shared Optical Network (TSON): A Programmable Network Edge Solution for Multi-Access Support
## 1 Introduction  
Towards Ultimate Convergence of All Networks (TOUCAN) [1] is a University of Bristol-led research project funded by the U.K. Engineering and Physical Sciences Research Council (EPSRC). The TOUCAN aims to achieve ultimate network convergence, enabled by a new technology agnostic architecture targeting a wide range of applications and end users. The architecture will facilitate optimal interconnection of any network technology domains, networked devices, and datasets with high flexibility, resource and energy efficiency, and the aim of satisfying the full range of quality of service (QoS) and quality of experience (QoE) requirements. With the rapid deployment of 5G and the emergence of beyond 5G technologies, telecom network infrastructures are being populated with heterogeneous types of access technologies supporting new types of services that often require high-bandwidth and low-latency key performance indicators (KPIs), for instance, high definition (HD), augmented reality (AR), and virtual reality (VR) services. As such, both last mile access (e.g., from edge to antenna) technologies, as well as fronthaul/backhaul and metro/core transport technologies, are also evolving to support these requirements. Due to latency and bandwidth requirements, optical networks are among the preferred transport technologies for both fronthaul/backhaul and metro/core network segments. However, there is a large variety of optical transport protocols and technologies that are being proposed by the industry and research communities to support fronthaul (e.g., common public radio interface (CPRI), evolved common public radio interface (eCPRI), time shared optical network (TSON)) and backhaul as well as metro and core requirements (TSON, orthogonal frequency-division multiplexing (O-OFDM), flexi-wavelength division multiplexing (WDM)). The choice of these technologies depends on the requirements that the wireless access technologies introduced in terms of bandwidth, latency, and other factors (e.g.,mmwave, multiple-input, multiple-output (MIMO), massive MIMO), as well as on the architecture of the various network segments. Additionally, with the maturity of virtualisation technologies and specifically network function virtualisation (NFV), most of the wireless networking functions such as mobile packet core are being virtualised for execution by commodity processors. To meet their latency requirements, they are required (or at least some components of them) to be hosted at the edge of the network. The aforementioned requirements indicate that there is an emerging requirement for a generic edge interface that can be programmed both at transport protocol level and also at the network function level. Such an interface can be deployed anywhere at the edge of the network, can interface any access technology at any backhaul/metro/core network, and can also host network functions that are sensitive to latency. TOUCAN, for the first time, has developed such an interface. A high-level architecture of the TOUCAN interface is shown in Figure 1.  
The TOUCAN realises its main vision by fulfilling the following four objectives:  
1. Develop a radically new architecture that will take a technology agnostic approach targeting cross-technology application, programmable infrastructure, and service composition driven by KPIs in, for example, capacity, connectivity, spectrum utilisation, energy efficiency, fairness, QoS, and QoE. 2. Converge heterogeneous technology domains seamlessly, specifically, wireless access and optical access, high capacity optical metro/backbone networks, data centre (DC) networks, and end devices. 3. Support very high bandwidth granularity range and capacity, from Pbps (e.g., inter-data centre transport) to kbps (e.g., machine-to-machine communications). 4. Break traditional barriers between infrastructure, control, and service layers by making the network infrastructure and its control part of the end-to-end service delivery chain. Figure 2 illustrates the generic TOUCAN architecture.