Optical inter-satellite link (ISL) with tens/hundreds Gbps is applied into LEO constellation to overcome the insufficient bandwidth of microwave ISL. Moreover, compared with GEO/MEO constellation, LEO constellation suffers from frequent topology switching because of the lowest orbital-altitude. Topology switching between adjacent topology snapshots is generally done through ISL handover (remove or establish ISL). However, service interruption caused by ISL handover within topology switching is a vital issue to address. After ISL handover occurs, isolated topology and slow route convergence (derived from long ISL delay and forwarding the updated message among hundreds/thousands of satellites) may cause severe service interruption. But considering the fact that time-varying topology is predictable and all the ISL handover could be pre-scheduled for topology management purpose, service interruption problem is investigated from the aspect of ISL handover and routing strategy in this paper. Owing to long establishing time of optical ISL, grouped optical ISL handover scheme is raised to decrease route convergence time during topology switching. Furthermore, predictive-update routing scheme based on Open Shortest Path First (OSPF-PUR) is proposed to minimize route convergence time for each ISL handover. For predictable ISL handover, in OSPF-PUR scheme, forwarding table is refreshed according to locally stored ISL handover information but without flooding. Simulation results illustrate that grouped optical ISL handover scheme reduces route convergence time within topology switching while topology connectivity is guaranteed. The route convergence time of ISL handover is effectively decreased by OSPF-PUR scheme. Besides, for OSPF-PUR scheme, packet loss rate remains unchanged while topology switching frequency increases.

To alleviate the performance interruption between elephant and mouse flows, a combined optical timeslot switching (OTS) and L2/L3 Top of Rack (ToR) architecture is experimentally demonstrated for the first time in a data center scenario. In this system, elephant flows are identified on the fly by a newly built sFlow-based traffic analyzer and delivered through a separate OTS subsystem. In this way, elephant flows are physically isolated from mouse flows; thus, fewer mutual interruptions are expected. However, previous OTS research has not sufficiently addressed how the timeslot allocator and timeslot allocation should be implemented to adapt to traffic fluctuations, and it is obvious that the current SDN-based timeslot allocation cannot satisfy the OTS system's requirements for time efficiency. Therefore, in this paper, data-plane development kit (DPDK) platform was used to enable an ultrafast online timeslot allocator (TSA) that can process timeslot requests at traffic levels exceeding 1 Tb/s. This demonstration employs two Intel Xeon CPU e5 logical cores for TSA, a private protocol between the TSA and servers and a novel timeslot allocation algorithm. Using the proposed architecture, mouse flows are seldom interrupted by elephant flows. The power penalty of the OTS system is less than 1.2 dB, which is acceptable for server-to-server interconnections. Furthermore, simulation results show that the system achieves a consistently lower end-to-end latency for all flows than does a traditional ToR-based intra-rack DCN.

Digital twin has revolutionized optical communication networks by enabling their full life-cycle management, including design, troubleshooting, optimization, upgrade, and prediction. While extensive literature exists on frameworks, standards, and applications of digital twin, there is a pressing need in implementing digital twin in field-deployed optical networks operating in real-world environments, as opposed to controlled laboratory settings. This paper addresses this challenge by examining the uncertain factors behind the inaccuracy of digital twin in field-deployed optical networks from three main challenges and proposing operational guidance for implementing accurate digital twin in field-deployed optical networks. Through the proposed guidance, we demonstrate the effective implementation of digital twin in a field-trial C+L-band optical transmission link, showcasing its capabilities in performance recovery in a fiber cut scenario.

In Elastic Optical Networks (EONs) with flexible bandwidth allocation, the blocking probability is high because of spectral contention. Similar to the functionality of wavelength conversion in Wavelength-Division-Multiplexing (WDM) networks, waveband conversion has been proposed to solve spectral contention in EONs. In this paper, we discuss the design of node architectures for an EON with waveband conversion. Four node architectures with shared Tuneable Waveband Converters (TWBCs) are proposed, and their blocking performances are evaluated by simulation. Simulation results show that the blocking probability of a node is significantly improved by waveband conversion. The sharing efficiency of waveband converters is also investigated. Simulation results show that at the same blocking rate, the node architecture with converters shared per node can save more than 20% waveband converters compared with that of the one with converters shared per link.

Recently, spatial-division-multiplexing (SDM) based on weakly-coupled multi-core or few-mode fibers has been proposed for short-reach switching scenarios, in which spatial mode can be used as an independent switching dimension. Fully-connected cross-connections (OXC) converting all spatial modes and wavelengths into one-dimensional switching ports and followed by huge switching array can provide non-blocking switching, but the hardware implementation is very complex and expensive. In this paper, we propose a layered OXC structure consisting of intra-mode sub-OXCs and inter-mode switching bridges. Then a scattered-spectrum-scan intra-mode-first routing and spectrum allocation (SSS-IMF-RSA) scheme is designed, in which only a few discrete spectrum segments instead of the whole spectrum should be scanned for spectrum allocation. The switching will be performed preferentially for the wavelength dimension because of mature switching capability and less searching time. We show by simulation that the proposed layered OXC with the SSS-IMF-RSA scheme can achieve similar blocking performance to fully-connected OXCs with up to 76.1% hardware scale reduction and 93% searching time reduction for network accommodation. The proposed OXC and RSA scheme greatly decrease the requirements for the port number of WSS and enable components reuse to achieve smooth evolution.