Optical Switching and Networking最新文献

Radio frequency (RF) spectrum is highly occupied and adding further broadband channels to fulfill the exiting user requirements has become difficult. Optical free-space communication can be regarded a possible alternative as it offers several potential advantages such as reliable connectivity, secure link, higher data rates, and large bandwidth. Consequently, free-space optical (FSO) communication system which is the most dominant optical wireless technology has become more attractive in current era to deploy additional broadband channels, and it can support bandwidth-hungry services. FSO has appealing benefits such as easy deployment, inherited secure communication, higher data rate, non-interfering link, and licensed-free large spectrum. FSO communication links are also susceptible to several meteorological situations including smog, fog, scintillation, smoke, snow, and dust. A critical research question is to ensure connectivity under these adverse circumstances. FSO communication is severally hampered by link attenuation, atmospheric turbulence, and line-of-sight (LOS) demands. To overcome these challenges, relay nodes can be employed to improve coverage area and error rate of FSO communication system. However, relay nodes cannot overcome pointing errors in FSO communication due to various critical factors such as building sway. To enhance the availability of FSO systems, a redundant backup RF link to form a hybrid network is a viable solution. The coexistence of both RF and optical system is proposed to tackle challenges as mentioned before and attain benefits of both spectrums. A hybrid FSO/RF technology is promising as it can substantially enhance the availability and reliability than individual channels and offers unique solution to high-throughput wireless connectivity, comparable data rates, and insensitivity to weather conditions. This hybridization approach can help both channels to jointly recover the deficiencies of each technology and secure efficient data transmission with highly variable channel conditions. The immediate switching in hybrid FSO/RF systems can enable suboptimal usage of FSO network. In this study, we examine switching techniques, routing protocols, channel models, and modulation schemes. We outline several projects discussed in literature and examine various application scenarios. Finally, we discuss potential challenges, physical layer security issues and associated practical solutions.

Free space optical (FSO) communication refers to the information transmission technology based on the propagation of optical signals in space. FSO communication requires that the transmitter and receiver directly see each other. High-altitude platforms (HAPs) have been proposed for carrying FSO transceivers in the stratosphere. A multihop HAP network with FSO links can relay traffic between ground FSO nodes. In this study, we propose an end-to-end switching model for forwarding traffic between massive pairs of ground FSO nodes over a HAP network. A protection mechanism is employed for improving the communication survivability in the presence of clouds, which may break the line of sight (LoS) between HAPs and ground nodes. We propose an algorithm to identify a set of necessary HAPs and to design the HAP network topology in integrating the protection mechanism. The design aims to a network with the minimal equipment cost. The results demonstrate that, even though networks with survivable capacity use more resources, they are not necessary much more expensive than those without survivability in terms of equipment, i.e., HAPs and FSO devices, and in terms of wavelength resource utilization.

10-Gigabit passive optical network (XG-PON) has emerged as an effective architecture to meet today's growing demand for bandwidth in the family of next-generation passive optical networks (NG-PON). It supports various quality of services such as voice, video live streaming, network browsing, etc., where these services demand bandwidth, which is limited. To overcome this limitation, bandwidth management schemes are employed by central authorities such as optical line terminals (OLT). Several dynamic bandwidth allocation (DBA) schemes exist for XG-PON in the literature, but these lack in detailed information about XG-PON and a comparison of various DBA schemes in one place. Therefore, this paper presents a detailed architecture of XG-PON and comprehensively reviews the existing dynamic bandwidth allocation schemes for the XG-PON system. This paper further identifies and implements majorly adopted bandwidth allocation schemes such as GIANT, X-GIANT, IACG, and EBU using a pre-existing module of XG-PON in the network simulator 3 (NS-3) simulation framework. The results have been obtained in two phases having different traffic scenarios, where, in phase 1, the load of all ONUs has been increased simultaneously, and in phase 2, the load of only one ONU has been increased. The obtained results have been analysed in terms of various network performance metrics. Hence, this paper reviews the available DBA schemes and provides a comprehensive analysis of the identified important DBA schemes.

Multicasting is inevitable in the advent of the age of online video streaming. Light trail, the unidirectional optical bus, enhances multicasting by facilitating sub wavelength granularity. Splitting a light trail into segments increases the bandwidth utilization. To remove the overburden of the auxiliary graph of the existing works lead the motivation of the proposed heuristic algorithm known as Dynamic Multicast Traffic Grooming and Split Light Trail Assignment (DMTG-SLTA), which further aims to reduce the blocking probability and other network resources while satisfying the dynamic connection requests. Simulation results are verified though numerical analysis and compared to the existing well known algorithms, thereby concluding the proposed work to be successful only after minimizing its computational complexity.

Fault management has long been an indispensable component for controlling and managing telecommunication networks. To prevent huge data losses, it is necessary to develop a fast and efficient fault localization mechanism. In this work, we study the problem of multi-failure localization in transparent optical networks. In this context, a correlation-based approach is introduced to exploit the quality of transmission of acquired lightpaths to localize the faulty links. The proposed search-based framework can be implemented by leveraging any search algorithm. One may utilize the exhaustive search method to localize faulty links more accurately, but at the cost of taking more time. On the other hand, one may utilize intelligent search methods with the aim of reducing the required time for localization at the expense of accuracy. However, we propose to use both of the search approaches together. In this way, faulty links are first localized by the intelligent search methods to reroute and restore the failed traffic as fast as possible to prevent further loss of data. To this aim, a genetic algorithm (GA) is proposed to search among the suspected links. Subsequently, exhaustive search method can be utilized to localize failures more accurately without time constraint and then send technicians to the right site to recover the faulty links. The obtained results reveal that the proposed GA approach achieves overall high localization accuracy (98.6%–100%) that is insignificantly affected as the traffic load decreases. Dual and triple-failure incidents are localized within 42–80 ms and 596–2180 ms, respectively. It is shown that the mean time required for localizing failures using the GA search algorithm is significantly lower than exhaustive search approach by several orders of magnitude. Hence, the proposed GA-based fault localization algorithm can reduce the average time required to restore the traffic in case of failures, applicable for the restoration applications.

The routing, modulation level, and spectrum allocation (RMLSA) problem is crucial for efficient elastic optical networks. This problem has been approached by optimal-and-non-scalable and sub-optimal-and-scalable solutions. In the second approach, we can distinguish the routing-based and permutation-based meta-heuristics. These approaches explore a sub-set of the RMLSA solutions, and consequently, the calculation of high-quality solutions can be limited.

This work proposes an RMLSA solution that considers the routing and request permutation simultaneously to explore a larger portion of the set of RMLSA solutions than state-of-the-art meta-heuristics. The proposed RMLSA solution is based on a genetic algorithm (GA) whose chromosome structure encodes routing and permutation genes.

Performance analysis of the proposed route-permutation-based GA (RPGA) has been compared to the state-of-the-art based on integer linear programming (ILP), route-based GA (RGA), and permutation-based GA (PGA) in offline and online traffic scenarios. Offline traffic simulations show that RPGA is promising since it obtains similar results to ILP. RGA gets worst as the traffic load increases compared to PGA and RPGA approaches. RGA, PGA, and RPGA achieve the same performance in all dynamic scenarios concerning blocking and entropy measures, given the set of requests is small.

Metropolitan optical networks are undergoing significant transformations to continue being able to provide services that meet the requirements of the applications of the future. The current deployment of the 5G networks and the envisioned 6G cyber–physical systems would expand the possibilities for offering IoT applications, autonomous vehicles, and smart city services while imposing strong pressure on the physical infrastructure. In order to guarantee the strictest quality of service and quality of experience requirements for users, new architectures have been proposed in the literature for metropolitan optical networks, with a growing interest in the last five years. However, due to the proliferation of a dozen new architectures in the last years, many questions need to be investigated regarding the planning, implementation, and management of these architectures, before they could be considered for practical application. This work presents a comprehensive survey of the new proposed single-layer (purely optical) architectures for metropolitan optical networks. First, we discuss the structural organization of the new metro ecosystems. Second, the already established and novel architectures are presented, highlighting their characteristics and application. Third, we carry out a comparative analysis of these architectures to identify future technological trends. Finally, we have drawn outstanding research questions to help direct future research in the field.

Time division multiplexed passive optical networks (TDM-PONs) such as EPON, XG-PON, XGS-PON, etc. have become widely accepted network architectures for meeting the bandwidth requirement of high-end consumer applications. The available bandwidth is still limited and needs to be utilized efficiently. There are scenarios when one ONU may completely dominate the network bandwidth leading to starvation of another ONUs. This may happen for an ONU in every allocation cycle. This enforces the OLT to provide such a fair allocation scheme that would provide a chance to different ONUs during polling and scheduling mechanism. This paper presents two novel DBA schemes namely the analytic hierarchy process proportional allocation scheme (AHP-PAS) and weighted sum model proportional allocation scheme (WSM-PAS) to determine the order of a transmission container (T-CONT) of an ONU for polling and scheduling. The proposed schemes are implemented in the network simulator (NS-3) and compared with the existing proportional allocation scheme (PAS) for inter-ONU and intra-ONU. The obtained results confirm that the proposed DBA schemes significantly improve the network performance in terms of delay fairness index, upstream mean delay, packet loss ratio, and packet jitter for T-CONT 2, 3, and 4.

In this paper, the joint problem of user association and power allocation for non-orthogonal multiple access (NOMA)-visible light communication (VLC) systems is investigated. First, a novel intelligent user association (UA) method for multi-user NOMA-VLC is proposed to improve the multiplexing efficiency. Second, a new adaptive optimal power allocation scheme based on the UA method is presented and three corresponding mathematical optimization problems are established, aiming to optimize the system throughput while each user's illumination requirement, quality of service demand, eye safety, and transmission power limit are satisfied simultaneously. Third, for the error propagation at the NOMA receiver, the perfect and imperfect interference cancellations are considered in the established power allocation models. Finally, the numerical results demonstrate the superiority of the proposed scheme on the VLC network capacity under perfect and imperfect interference cancellation. Furthermore, it is also found that the proposed scheme could achieve higher system throughput by modifying users' field-of-views (FOVs).

The rise of traffic intensive services and applications is pushing the limits of conventional single band Wavelength Division Multiplexing (WDM) optical networks. As an answer to this challenge, new data plane technologies are being investigated. Multi-band optical networks have raised as a very interesting candidate due to the potential increased capacity they offer thanks to the exploitation of multiple bands of the optical spectrum. Considering the whole telecom ecosystem, multi-band optical networks will coexist with other technological segments (e.g., Radio Access Network (RAN)) with the aim of provisioning services across the end-to-end infrastructure. With the advent of 5G and beyond 5G (B5G) architectures, novel provisioning paradigms are taking preponderance, such as the case of network slicing, which represents a radical paradigm change with respect to legacy business and provisioning models. As such, proper solutions for supporting network slice provisioning and runtime maintenance at the data plane are required. With this in mind, in this paper we present a control and orchestration architecture for the configuration and maintenance of network slices in multi-band optical networks, in support of B5G end-to-end services. Indeed, quality assurance and maintenance at all levels is seen as a cornerstone in B5G architectures. Thus, proper mechanisms adapted to the nature of the underlying sliceable multi-band data plane are required to ensure the quality of deployed slices. In this regard, we also present a novel band-adaptive protection scheme which takes advantage of the properties of the multi-band data plane so as to enhance the robustness of slices against quality degradations. We showcase the provisioning and maintenance of multi-band optical network slices by means of an experimental demonstration in a real testbed deployed at our premises. In addition, we evaluate the performance of the proposed band-adaptive protection scheme for slice quality assurance in front of other strategies by means of extensive simulation analysis in larger network scenarios.