Add/Drop Flexibility and System Complexity Tradeoff in ROADM Designs

Rapid development of optical communication techniques has made possible large scale wavelength routing optical networks. Nowadays, these networks are deployed worldwide. Large scale networks have natural hierarchies due to either geographical reasons or administrative consideration and are therefore managed in a hierarchical way correspondingly. That is, networks are composed of several subnetworks, which are themselves composed of other even smaller subnetworks. Erlang fixed point approximation (reduced load approximation) has been extensively used in performance evaluation of end to end call blocking probability in traditional circuit switching networks, which are also called loss networks. This method has also been extended for hierarchical loss networks. However, performance evaluation of call blocking probability in hierarchical wavelength routing optical networks has not yet been presented. In this paper, a kind of approximation method is developed for analyzing end to end call blocking probability in hierarchical wavelength routing optical networks. By iteratively running processes combining a top-down load distribution and a bottom-up calculation of node-pair blocking in the network hierarchy, a steady state will be reached and approximate end to end call blocking probability in hierarchical wavelength routing optical network is obtained. Both the link independent model and the link correlation model are used in our analysis. By comparing theoretical results derived from our approximation method and results obtained from discrete event simulation, we illustrate that our method gives reasonable estimate of end to end call blocking probability in hierarchical wavelength routing optical networks, with the correlation model giving much more accurate estimate than the independent model.

While a session request is assigned to a wavelength-routed optical WDM networks, which are circuit-switched in nature, the challenge of routing and wavelength assignment (RWA) is to calculate the optimal path between two nodes, and further is to assign an available set of wavelengths along this path. An algorithm called Total wavelengths and Expected available wavelengths (TEW) proposed by Pavarangkoon et. al. in order to achieve effective routing and wavelength assignment formulates a link weight function and considers this as the main factor for route selection. This function is calculated by using a determination factor of the number of wavelengths that are being used currently and are supposed to be available after a certain time. However, this algorithm tends to overload paths with smaller weights and higher utilization while lightly loaded paths with slightly lower capacities may remain unused. In this paper, propose an improvement to the TEW algorithm by incorporating the frequency of usage of the paths in the weight function and running Dijkstra’s shortest path algorithm to choose paths that have more total and expected available wavelengths and less frequency of usage. The proposed algorithm is called as Countered Total wavelengths and Expected available wavelengths (CTEW) algorithm. The impact of the proposed algorithm on blocking probability is investigated by means of computer simulation and by comparing it with TEW algorithm. The results show that the proposed algorithm can achieve better performance in terms of blocking probability.

With the emergence of bandwidth intensive applications new methodologies need to be developed for improvement of network blocking performance, without supplying extra resources in dynamic wavelength-division-multiplexing (WDM) networks. Rerouting is one among the viable and cost-effective solutions to reduce the blocking probability (BP) of optical WDM networks. Similarly, set-up delay tolerance, a metric of service level agreement (SLA) has been exploited in [1]-[3] for improvement in network BP. In this paper, we study the rerouting in dynamic WDM network and analyze two different lightpath rerouting strategies. Moreover, we investigate further improvement in network BP by exploiting these rerouting techniques for network provisioned with set-up delay tolerance. Through extensive simulation studies, we confirm that the rerouting strategies decrease the BP substantially for network provisioned with set-up delay tolerance, even for smaller set-up delay tolerance value i.e. when the connection requests are impatient to wait for provisioning in the network. However, it also reduce BP significantly even when the network is not provisioned with set-up delay tolerance.

We study a dynamic WDM network with nonideal components in the physical layer which uses an impairment-aware routing and wavelength (RWA) algorithm for connection provisioning. We investigate the reduction in blocking probability (BP) by utilizing service Level Agreement (SLA) metric i.e. setup delay tolerance during connection provisioning. Furthermore, we explore the improvement in the network performance by efficiently utilizing the knowledge of the connections holding-time, another metric of SLA. Keeping in mind that BP reduction can be obtained by set-up delay tolerance [1] our focus is to investigate how set-up delay tolerance combined with holding-time awareness can improve BP performance caused by physical impairment. Our simulation results confirm that significant improvement can be achieved by holding-time aware connection provisioning compared to the unaware holding-time case. Moreover as expected, set-up delay tolerance can reduce BP even without knowledge of connections holding-time.

Advances in Grid technology enable the deployment of data-intensive distributed applications, which require moving terabytes or even petabytes of data between data banks. The current underlying networks cannot provide dedicated links with adequate end-to-end sustained bandwidth to support the requirements of these Grid applications. DWDM-RAM is a novel service-oriented architecture, which harnesses the enormous bandwidth potential of optical networks and demonstrates their on-demand usage on the OMNInet. Preliminary experiments suggest that dynamic optical networks, such as the OMNInet, are the ideal option for transferring such massive amounts of data. DWDM-RAM incorporates an OGSI/OGSA compliant service interface and promotes greater convergence between dynamic optical networks and data intensive Grid computing.

In this work, two Markov chains modeling packet delay have been developed to obtain closed-form solutions for packet loss probabilities and packet delay distributions in a real-time wireless communication environment. Packets with delay constraints are queued at the source and are transmitted one by one with possible retransmissions to correct errors. The first model models packet delay and correlated packet arrivals using a one-dimensional Markov chain. Usually, at least two dimensions are needed in queuing models. The second model is a two-dimensional Markov chain modeling packet delay, correlated channel errors, and correlated arrivals. Both correlated errors and arrivals are known to have significant impact on packet loss. Possible applications of the results are also discussed.

In this paper, we developed an analytical model of a time-threshold based bandwidth allocation scheme for data calls in cellular networks. The scheme is based on monitoring the elapsed real time of handoff calls and according to a time threshold parameter, handoff calls are either prioritized or treated as new calls. The scheme is modeled using a onedimensional markov chain and numerical analysis is presented to estimate blocking probabilities of new calls, dropping probabilities of handoff calls and system utilization. The scheme is simulated under different network conditions. It is observed that analytical results closely match the simulation results. The results show that the proposed scheme yields a considerable enhancement in terms of performance/cost ratio when compared with the conventional schemes.

In intelligent transportation systems, wireless connected vehicles moving in platoons can improve roads' throughput. For managing driving status of the platoon, a lead vehicle transmits driving information to following autonomous vehicles by using multi-hop data dissemination. We study a novel data dissemination protocol which investigates a chain-based transmit rate control to reduce data dissemination latency. The optimal resource allocation algorithm is formulated to minimize the total dissemination latency of the platoon under guaranteed bit error rates, and can be judiciously reformulated and solved using standard optimization techniques. A novel dynamic programming algorithm is presented to solve the platooning resource allocation optimization, which uses backward induction to significantly reduce the resource allocation complexity. In addition, we interpret the vehicular platoon as one-dimensional Markov chain, and derive a closed form of dissemination latency. Simulations are carried out to evaluate the performance of the proposed dynamic programming algorithm. The numerical results show that our algorithm achieves optimal solutions with cutting off the complexity by orders of magnitude, while improving dissemination rate in the vehicular platoon.

Wavelength-selective switches (WSSs) are the key wavelength-routing components in optical meshed networks. We discuss possible architectures for WSSs that support multimode fibers, and related tread-offs between key switch characteristics like spectral passband, number of switching ports, and insertion loss. We also present experimental results for WSSs that support few-mode fibers with 3 spatial modes.

Most works on financial forecasting use information directly associated with individual companies (e.g., stock prices, news on the company) to predict stock returns for trading. We refer to such company-specific information as local information. Stock returns may also be influenced by global information (e.g., news on the economy in general), and inter-company relationships. Capturing such diverse information is challenging due to the low signal-to-noise ratios, different time-scales, sparsity and distributions of global and local information from different modalities. In this paper, we propose a model that captures both global and local multimodal information for investment and risk management-related forecasting tasks. Our proposed Guided Attention Multimodal Multitask Network (GAME) model addresses these challenges by using novel attention modules to guide learning with global and local information from different modalities and dynamic inter-company relationship networks. Our extensive experiments show that GAME outperforms other state-of-the-art models in several forecasting tasks and important real-world application case studies.

This paper has clarified the simulation study of optical time division multiplexing/wavelength division multiplexing system based static/dynamic optical transparent networks demonstration through all-optical fiber amplifiers. Received signal power per channel is measured against network reach for both static and dynamic networks in the presence of all-optical Raman/erbium doped fiber amplifier/semiconductor optical amplifier amplifiers. Data rate transmission per channel is demonstrated against repeater spacing for all proposed optical fiber amplifiers based on various near infrared operating wavelengths for both static and dynamic optical transparent networks. In addition, the overall signal per noise ratio is clarified in relation to network throughput and various near infrared operating wavelengths for the static and dynamic transparent optical network based on all proposed amplification techniques. Moreover, the overall system bit error rate is studied and tested against network throughput and various near infrared operating wavelengths for both static and dynamic transparent optical networks based on all proposed amplification techniques.

An analytical model for calculating capacity in multi-cell UMTS networks is presented.Capacity is maximized for different spreading factors and for perfect and imperfect power control.We also design and implement a local call admission control (CAC) algorithm which allows for the simulation of network throughput for different spreading factors and various mobility scenarios.The design of the CAC algorithm uses global information; it incorporates the call arrival rates and the user mobilities across the network and guarantees the users' quality of service as well as pre-specified blocking probabilities.On the other hand, its implementation in each cell uses local information; it only requires the number of calls currently active in that cell.The capacity and network throughput were determined for signal-to-interference threshold from 5 dB to 10 dB and spreading factor values of 256, 64, 16, and 4.

Current optical transport networks provide high bandwidth through the use of advanced WDM technology, but are difficult to adapt to the different statistical patterns and quality of service (QoS) demands of future traffic. There has been much debate whether the use of dynamically reconfigurable optical networks would have a number of advantages in accommodating the needs of future traffic demands. Dynamic networks would eliminate the need for frequent opto-electronic conversion in current networks, and may save resources through higher utilization and fast adaptation. Different architectures have been proposed to address this problem: Wavelength-routed optical networks (WRON), optical burst switching (OBS), and optical packet-switching (with increasing granularity and speed of reconfiguration). In this paper we investigate whether these architectures are suitable (necessary?) to meet the demands of future traffic, using an analysis focusing on both modeling and experimental aspects.

Survivability in waveband switching optical networks: Challenges and new ideas

The paper presents energy efficient routing in dynamic optical networks, where solar energy sources are employed for the network nodes. Different parameters are evaluated, including the number of nodes that have access to solar energy sources, the different maximum solar output power, traffic type and the locations of solar powered nodes. Results show a maximum 39% savings in energy consumption with different increases in connection blocking probability.