Following successful adoption of cloud computing, many service providers (SPs) are now using high-performance Virtual Machines (VMs) located in large datacenters owned by public cloud infrastructure providers to deploy their virtual network functions (VNFs). Since using these VMs has a cost depending on utilization time, a complex problem of VNF placement and scheduling (VPS) must be addressed to achieve satisfactory network performance (e.g., latency) while minimizing the cost paid to lease VMs. In this study, a cost-efficient VPS scheme (CEVPS) is proposed to address the VPS problem in public cloud networks considering dynamic requests of ordered sequences of VNFs. Our CE-VPS scheme goes beyond existing solutions as it models some important practical aspects such as an additional latency incurred by booting a VM and installing a VNF instance. Also, CE-VPS considers that VNFs can be multi-threaded or single-threaded, and that their throughput as a function of allocated computing resources must be modeled differently. CEVPS is formulated as a mixed inter linear program (MILP) and also as an efficient heuristic algorithm. CE-VPS achieves lower cost and latency than conventional Best-Availability and Cost- Efficient Proactive VNF Placement schemes, and a better tradeoff between resource consumption and latency performance than a conventional Low-Latency scheme.

To quantitatively measure content connectivity and provide protection for different kinds of content, the concept of k-node (edge) content connectivity is proposed recently. Based on k-node (edge) content connectivity, k-node (edge) content connected elastic optical datacenter network (KC-EODN) is proposed to design disaster-resilient and spectrum-efficient optical datacenter networks. In KC-EODN, k independent end-to-content paths are established for each request. However, it will consume too much resource to assign dedicated spectrum for each end-to-content path. Spectrum sharing among multiple end-to-content paths of different requests can greatly improve resource efficiency. In this paper, a novel perfect matching based sharing principle among multiple end-to-content paths of different requests is proposed. Based on the new proposed sharing principle, we present the shared end-to-content backup path protection (SEBPP) scheme for KC-EODN. Integer linear program (ILP) model and heuristic algorithms are designed for SEBPP scheme with the objective of minimizing the total of working and backup spectrum resources. Numerical results show that the proposed SEBPP scheme can greatly reduce spectrum consumption while ensuring the survivability against natural disaster and multi-failures.

The sub-tree-based optical multicasting scheme provides a spectrum-efficient approach to providing emerging multicast services in optical data center networks. Moreover, multicast services are usually replicated and maintained in multiple geographically distributed data centers to improve its access efficiency and reliability. Therefore, the source data centers of all constructed sub-trees for a multicast demand are not confined to a common data center and can be independently determined by the requested distribution. In this paper, we study the problem of multicast service provisions while leveraging multicast service backups among multiple geographically distributed data centers. A novel distributed sub-tree-based optical multicasting (DST-OM) scheme is proposed. An integer linear program (ILP) model is developed for the DST-OM scheme with the aim of minimizing the total spectrum consumption of all multicast demands in elastic optical data center networks (EO-DCNs). We also define the minimum spectrum subtree (MSST) problem for the DST-OM scheme. Two modulation-level-aware heuristic algorithms are developed to address the MSST problem. Numerical results show that the DST-OM scheme achieves higher spectrum efficiency and lower blocking probability than the conventional common source sub-tree-based optical multicasting (CSST-OM) scheme and the single-tree-based optical multicasting (ST-OM) scheme.

The SFC deployment problem has proved to be NP-hard and has attracted great research interests. At present, most existing studies focus on deploying SFC through virtual network functions (VNFs) and few studies involve hybrid VNF and physical network function (PNF) environment. However, in the transition to a comprehensive network function virtualization (NFV) network, hybrid VNF and PNF environment is possible and important. Currently, VNF and PNF both play an important role in todays cloud networks. PNF is far superior in processing speed, but VNF has advantages in flexibility and cost. Using VNF or PNF alone may not meet user needs, affecting user experience and system performance. Hence, this paper studies the SFC deployment problem in hybrid VNF and PNF environment. A cost and latency customized dynamic SFC deployment (CLSFCD) scheme is proposed. Instead of giving priority to the PNF or the VNF roughly, the CL-SFCD scheme maps network functions to VNFs or PNFs according to the SFC requesters personalized demands to satisfy the demands of different users. It aims to minimize the weighted value of total cost and latency. The CL-SFCD scheme is formulated as a mixed integer linear programming (MILP) model for exact results. Heuristic algorithms are developed to provide an approximate optimal solution in large-scale cloud networks. Numerical results show that the CL-SFCD scheme achieves performance that balances cost and latency based on user requirements than the VNFonly, VNF-GA, and PNF-only deployment schemes.

In the past decade, rapid advancements in communication technology have fundamentally transformed methods of connection and communication in the digital age. Optical networks have emerged as indispensable communication infrastructures due to their high per-channel transmission rates, massive aggregate capacity enabled by multiplexing technologies, and excellent resistance to electromagnetic interference. The enormous transmission capacity of optical networks has greatly facilitated the development of various businesses and applications. Therefore, ensuring the reliable operation of optical networks is crucial. One of the key conditions for ensuring the reliable operation of optical networks is the ability to accurately measure or evaluate their reliability. There are many methods for the evaluation of optical network reliability. Each method has its applicable scope, advantages, and limitations. However, with the continuous development of new technologies like 6G, reliability evaluation will face higher demands and more complex scenarios. Currently, there is no comprehensive systematic literature survey on the existing optical network reliability evaluation methods. Hence, the research focuses on evaluation methods for optical network reliability. Several essential concepts in evaluating optical network reliability are clarified, factors affecting its reliability are summarized, evaluation metrics are analyzed, and evaluation methods are reviewed. Then, methods to enhance the reliability of optical networks are outlined, and the trade-offs between cost/energy consumption and reliability are discussed. Finally, some significant future challenges are described, and corresponding open research topics are proposed. This survey provides valuable references for designing more reliable optical networks or developing highly reliable operation and maintenance strategies.

In satellite optical networks (SONs), laser inter-satellite links (LISLs) are energy hungry to drive pointing, acquisition, and tracking systems and laser devices to maintain fine link pointing and provide communication services. Rechargeable batteries are the sole energy support for satellites in the eclipse region, and unrestrained use of batteries may accelerate battery aging and shorten the satellite operation period. Real-time sleep/activate control on demand is not applicable to reduce the energy consumption of LISLs because waiting for link pointing delay is intolerable for most traffic requests, and aperiodically changing LISLs’ working states may affect the routing reliability in SONs. For the above problem, this paper proposes green LISL planning (GreenLP) to periodically switch LISLs’ working states to prolong the battery lifetime. Considering the possible degradation of network throughput by sleeping LISLs, this paper models GreenLP as a double-objective optimization problem from the perspective of topology design, and two topology features are expanded based on traffic prediction to numerically quantify LISLs’ potential importance. Simulation results indicate that, compared with existing schemes, GreenLP reduces battery lifetime consumption by 8.93% and the probability of request blocking by 5.65%. Numerical analysis shows that the expanded node betweenness centrality has the effectiveness and universality to quantify LISLs’ potential importance on network throughput.