# Time Shared Optical Network (TSON): A Programmable Network Edge Solution for Multi-Access Support
## 1 Introduction
In this architecture, the TOUCAN converged physical infrastructure aims to design a generalised solution able to deliver agility, programmability,  
Figure 1: A high-level architecture of the Towards Ultimate Convergence of All Networks (TOUCAN) interface. SDN: software defined networking, CPRI: common public radio interface, eCPRI: evolved common public radio interface, TSON: time shared optical network, Flexi WDM: flexi-wavelength division multiplexing, BW: bandwidth, OBSAI: open base station architecture initiative, OTDM: optical time domain multiplexing, O-OFDM: optical orthogonal frequency-division multiplexing. and flexibility for interfaces between heterogeneous transport technologies, that is, optical and wireless, and different networks--for example, optical core, metro and access; wireless cellular; and wireless local area networks. Figure 3 presents the architecture of the generic convergence-node with multiple interfaces to fulfil the TOUCAN-converged physical infrastructure illustrated in Figure 2. In this scenario, the node is implemented on field-programmable gate arrays (FPGAs) to provide the flexibility and the requests for future network convergence. In addition, the node interface takes advantage of the huge input-output (IO) resource and hardware programmability of FPGAs. Through high speed transceivers, the FPGA could process the incoming traffic from Ethernet, access, wireless cellular, and other networks. Then, the FPGA could use its computing power to perform traffic parsing, protocol framing/mapping, traffic aggregation, and other operations. Moreover, the convergence node aims to allocate resources elastically in time, spectrum, and space, in order to accommodate a large range of traffic profiles and granularities in an efficient way and providing low latency on the basis of considered vertical technology interfaces. Finally, the processed data traffic will drive different bandwidth variable transmitters (BVTs) to generate optical signals for transmission towards different networks. The TSON solution [2; 3] is a proprietary solution developed by the High Performance Networks (HPN) research group, currently part of Smart Internet Lab, University of Bristol, and has been adapted to support the convergence node proposed in Figure 3. This technology offers high bandwidth and low-latency connectivity to support the requirements of High-Performance Networks. The TSON solution is a proven active WDM solution that provides variable sub-wavelength switching granularity and the ability to dynamically allocate optical bandwidth elastically. This solution is the first multiple protocol programmable interface that meets 5G KPIs such as high bandwidth and sub-millisecond end-to-end latency [4]. Several extensions have been applied to the TSON architecture over the course of the TOUCAN project to equip this solution with more features. This work describes the TSON solution capabilities and reviews its evolution stages. The rest of the paper is structured as follows: Section 2 introduces the initial TSON solution implementations. In this section, we describe TSON extensions organised in four stages of evolution. Section 3 presents the current status of the TSON implementation. In this section,  
Figure 2: The generic TOUCAN architecture. TE: traffic engineering, IETF: internet engineering task force, ONF: open networking foundation, SNMP: simple network management protocol, IMF: internet message format. the latest TSON architecture is introduced and its evaluation results are presented. The TSON control plane is introduced in Section 4. Finally, Section 5 concludes the paper.