Full Wavelength Conversion Research Articles

Simulation of Coherent Electromagnetic Waves in Wavelength Division Multiplexing (WDM) Transmission

This study analyzes the application of Wavelength Division Multiplexing (WDM) in fiber optic networks which aims to find the wavelength, WDM optical spectrum and modes, as well as the CPR estimated phase and modes. In this study WDM allows the simultaneous transmission of different data streams through a single optical fiber, using different wavelengths. This research was conducted using the python OptiCommPy module. This module is used to perform modeling of complex optical fiber transmission systems by considering the various parameters and disturbances involved in optical transmission. The results obtained from this study are that WDM networks can use full or limited wavelength conversion, depending on the wavelength conversion capability of each network node. Whereas multifiber networks use fiber pools between network nodes, and multifiber WDM networks can be implemented without or with full wavelength conversion. This research can be a guide for designing coherent electromagnetic waves in WDM transmissions using the OptiCommPy python module.

Wavelength Selective Switch-Based Clos Network: Blocking Theory and Performance Analyses

A Clos network is a classical switching network often used in conventional electrical switches. In a Wavelength Selective Switch (WSS) based Clos all-optical switching network, the wavelength dimension needs to be additionally considered. However, the conventional blocking theory of the Clos network may not be valid in this scenario and it may be necessary to conduct a theoretical study specifically for the WSS-based Clos all-optical switching network. In this paper, we derive the strictly non-blocking conditions for the WSS-based Clos network for the cases where there is no wavelength conversion, partial wavelength conversion, and full wavelength conversion. For the situation where there is service blocking, we also formulate probabilistic analytical models to estimate the blocking performance for the three types of WSS-based Clos networks. The gain of transceiver utilization achieved by the WSS-based Clos network with wavelength conversion is evaluated and compared with that of one without wavelength conversion. We also evaluate the impact of partial wavelength conversion capability on the blocking performance of a WSS-based Clos network.

Performance Modeling of Diversity Coded Path Protection in OBS/OPS Networks

In bufferless optical burst/packet switched (OBS/OPS) networks, data (bursts or packets) may be lost due to contention or equipment failure. Diversity coding-based path protection schemes can be used to protect data from a single-trunk failure with potentially more efficient resource utilization compared to dedicated (e.g., 1 + 1) path protection schemes and help reduce the burst/packet loss ratio. This paper provides a scalable and accurate burst/packet loss ratio approximation based on the Erlang fixed-point approximation for networks that employ protection based on diversity coding and for networks that employ protection based on both diversity coding and 1 + 1 path protection. We use discrete event simulations to assess the accuracy of the approximation based on a wide range of scenarios in a 10-node circular lattice and NSFNet networks. Further, we discuss the effect of parameter settings and the effect of the choice of the wavelength selection method on the accuracy of the approximation. We consider scenarios without wavelength conversion and with full wavelength conversion and two types of users: premium and regular. The premium users, typically of mission critical services, receive protection while the regular users do not. We compare diversity coding and 1 + 1 path protection in a 10-node circular lattice network. The results show that for this example network, for the premium users and under low traffic load, the burst/packet loss ratio in OBS/OPS networks is lower for diversity coding compared to 1 + 1 path protection. However, under heavy traffic load, we observe a lower loss ratio for the case of 1 + 1 path protection.

Dropping probability reduction in OBS networks: A simple approach

In this paper, we propose and derive a slotted-time model for analyzing the burst blocking probability in Optical Burst Switched (OBS) networks. We evaluated the immediate and delayed signaling reservation schemes. The proposed model compares the performance of both just-in-time (JIT) and just-enough-time (JET) signaling protocols associated with of void/non-void filling link scheduling schemes. It also considers none and limited range wavelength conversions scenarios. Our model is distinguished by being adaptable to different offset-time and burst length distributions. We observed that applying a limited range of wavelength conversion, burst blocking probability is reduced by several orders of magnitudes and yields a better burst delivery ratio compared with full wavelength conversion.

Near-Optimal Algorithm for Group Scheduling in OBS Networks

Group scheduling is an operation whereby control packets arriving in a time slot schedule their bursts simultaneously. Normally, those bursts that are of the same wavelength are scheduled on the same channel. In cases where the support of full wavelength converters is available, such scheduling can be performed on multiple channels for those bursts that are of an arbitrary wavelength. This paper presents a new algorithm for group scheduling on multiple channels. In our approach, to reach a near-optimal schedule, a maximum-weight clique needs to be determined; thus, we propose an additional algorithm for this purpose. Analysis and simulation results indicate that an optimal schedule is almost attainable, while the complexity of computation and that of implementation are reduced.

Scheduling Based on Minimal Conversion Degree With Respect to Wavelength Conversion and Coding in Optical Multicast Node

Optical multicast collision occurs more frequently for the replication and forwarding of optical multicast increase in the switch node. In this letter, an optical multicast switching node architecture configured with wavelength conversion and network coding is proposed. The proposed node architecture uses a group of output shared wavelength converters in the wavelength domain and a group of feedback shared encoders to resolve the optical multicast collision. To minimize the total conversion degree, we propose an improved algorithm, maximal weighted stable set, to assign wavelength converter with respect to the wavelength conversion degree as the weight. Concretely, the graph coloring matching algorithm is used to select the wavelength converter with minimal wavelength conversion degrees. Compared with the node architecture with two layers wavelength conversion and with full range wavelength conversion, analyses and simulation results show that the proposed node architecture largely reduces the packet loss probability with low cost of wavelength conversion and results in a better performance to solve multicast collision.

PERFORMANCE ANALYSIS OF WSXC AND WIXC SSM OXC IN WDM OPTICAL NETWORKS

The impact of inband crosstalk on an optical signal passing through optical cross-connect nodes (OXC’s) in wavelength division multiplexing (WDM) optical network, is studied from the equation of electric field with crosstalk and the corresponding current. The analysis has been done for two SSM (space switching matrix) OXC architecture namely WSXC & WIXC where later one has full wavelength conversion capability. Although WIXC attenuates more crosstalk though it is found that depending on the values of optical propagation delay differences, coherent time of lasers and time duration of one bit of the signal, the required power penalty in WIXC may be greater than that of WSXC in some cases. The analysis has been performed on the measures of Bit Error Rate (BER) and Power Penalty.

Group Scheduling for MultiChannel in OBS Networks

Group scheduling is a scheduling operation of optical burst switching networks in which the burst header packets arriving in each timeslot will schedule their following bursts simultaneously. There have been many proposals for group scheduling (such as OBS-GS, MWIS-OS and LGS), but they consider mainly to schedule the arriving bursts which have the same wavelength on an output data channel. Another suggestion is GreedyOPT which considers the group scheduling for multichannel with the support of full wavelength converters, but it is not optimal. This article proposes another approach of group scheduling which is more optimal and has a linear complexity.

Blocking RWA Model Analysis in Irregular OTN Topology

Wavelength converters (WC) that configured on the nodes can make the same wavelength optical channel from the continuity constraints, if it is configured suitable, it will effectively reduce the network congestion ratio. In this paper, we investigate the sub graph algorithm with blocking RWA model for the large capacity optical transport. Because the price is more expensive WC, it can not be deployed in all nodes considering the increasing costs and maintenance complexity. We investigated is the WC configuration during network construction, with only part of the network node configuration. The studies show that the rational allocation of part of the WC can get nearly the same performance as the full wavelength conversion network.

Performance Evaluation of an Optical Burst Switched Core Node With Generalized Arrivals and Partial Wavelength Conversion Capability

Many of the burst assembly algorithms employed in optical burst switching (OBS) networks preserve the IP traffic self-similarity property in the burst traffic. We introduce a mathematical model for performance evaluation of an OBS core node employing either no, a partial or a full wavelength conversion strategy. The model assumes long-range dependent (LRD) traffic arrivals to the OBS intermediate node whose inter-arrival times are accurately modeled by a Pareto distribution, whereas exponential holding times are assumed. In our proposed model, each output port in the node is modeled as a GI/M/w/w queue with partial server accessibility. An imbedded Markov chain approach is used to derive the limiting state probability distribution for the number of bursts currently served by an output port as seen by arriving bursts. Next, the average burst loss probability is evaluated from steady-state occupancy probabilities. In addition, the results of our mathematical model are validated via simulation. Furthermore, the results of the model are compared with those when assuming short-range dependent Poisson arrivals. Comparison shows that traditional Poisson traffic models yield over-optimistic performance measures compared to the LRD Pareto traffic models, especially for light traffic scenarios. Furthermore, we study the impact of varying different traffic parameters, such as the average arrival rate and the Hurst parameter, on the burst loss probability. Finally, the impact of varying the wavelength conversion capability on the burst loss probability is studied, where we compare two strategies for contention resolution: adding new channels (wavelengths) or adding wavelength converters, while taking the cost into consideration.

Dynamic Routing and Wavelength Assignment in Multifiber WDM Networks with Wavelength Conversion Capability

This paper proposes a dynamic routing and wavelength assignment (RWA) scheme in multifiber WDM networks with wavelength conversion capability. In multifiber WDM networks, each link consists of multiple fibers. Thus, multiple lightpaths with the same wavelength can be established in the same link as long as they use different fibers. In WDM networks with wavelength conversion, the network nodes have wavelength conversion capability which can convert one wavelength to another. In order to efficiently utilize multifiber and wavelength conversion capability, an appropriate RWA scheme is necessary. The proposed scheme provides RWA for multifiber WDM networks with sparse and full wavelength conversion capability. In the proposed scheme, a route and wavelengths are selected for each lightpath based on wavelength availability and location of nodes with wavelength conversion capability. Through simulation experiments, we show that the proposed scheme reduces the blocking probability of lightpath establishment efficiently.

부분적 광파장 변환 노드를 이용한 광인터넷 복구

This paper studies the effects of wavelength conversion on self-healing optical networks. We examined the effects of wavelength conversion capability on the backup routing and the spare wavelength utilization. The efficiency of spare wavelength utilization is proportionally increased as the wavelength conversion capability increases, different from the call blocking probability for which about 30% of wavelength conversion capability shows nearly the same performance as full wavelength conversion capability. The spare resource utilization efficiency can be improved by using alternate routing and wavelength assignment algorithms.

Fluid limit of an asynchronous optical packet switch with shared per link full range wavelength conversion

We consider an asynchronous all optical packet switch (OPS) where each link consists of N wavelength channels and a pool of C ≤ N full range tunable wavelength converters. Under the assumption of Poisson arrivals with rate λ (per wavelength channel) and exponential packet lengths, we determine a simple closed-form expression for the limit of the loss probabilities P loss (N) as N tends to infinity (while the load and conversion ratio σ=C/N remains fixed). More specifically, for σ ≤ λ 2 the loss probability tends to (λ 2 -σ)/λ(1+λ), while for σ > λ 2 the loss tends to zero. We also prove an insensitivity result when the exponential packet lengths are replaced by certain classes of phase-type distributions. A key feature of the dynamical system (i.e., set of ODEs) that describes the limit behavior of this OPS switch, is that its right-hand side is discontinuous. To prove the convergence, we therefore had to generalize some existing result to the setting of piece-wise smooth dynamical systems.

Variable neighbourhood search for resolving routing and wavelength assignment problem in optical wavelength-division multiplexing networks

The issue of finding optimal signal routes is one of the main challenges within the framework of optimal networks. This study aims at illustrating the development of a new, mixed-integer mathematical model for solving the static routing and wavelength assignment (RWA) problem in optical wavelength-division multiplexing (WDM) networks and presents the comparison of results obtained by heuristics and CPLEX commercial software. The objective function of the mathematical model is to minimise the blocking probability by maximising the number of successfully connected lightpaths. In this paper two WDM networks with full wavelength conversion nodes were tested. The proposed heuristics are the variable neighbourhood search (VNS) and tabu search (TS). Firstly, the authors compare the results obtained by these two heuristics and CPLEX on a low-complexity WDM network, aiming to determine whether these heuristics may yield results which approximate optimal results. Secondly, having illustrated that the heuristics provide satisfactory results, the authors run these heuristics on a high-complexity WDM network. The results indicate minor differences in blocking probability and show that in majority cases, VNS spends ten times less CPU time as opposed to TS. In conclusion, the authors argue that VNS heuristic is appropriate for resolving this static RWA problem.

Loss Differentiation in Full Wavelength Conversion Capable OBS Networks by Burst Cloning

Most of the QoS differentiation proposals for OBS are built upon a few traditional basic mechanisms. We propose a novel basic differentiation mechanism, Time domain Cloning Differentiation (TCD), based on the cloning concept. TCD evolves our previous QoS-MWST proposal, which was only applicable in limited and no wavelength conversion capable networks. TCD can also be used with full wavelength conversion capability. We also develop an analytical model of TCD in a single link, and present Proportional differentiation TCD, which provides edge-to-edge proportional loss differentiation based on TCD. We show that TCD outperforms other basic differentiation mechanisms.

A new multi-granularity traffic grooming routing algorithm in IP over WDM networks

In IP over WDM networks, since there is a large bandwidth gap between a wavelength capacity and the actual bandwidth required by each user, it is necessary to multiplex low-rate traffic streams (LRSs) into lightpaths by traffic grooming. However, with the number of wavelengths increases, a large number of all optical (OOO) transmitting ports are consumed. Meanwhile, the multi-hop grooming with incorporating full-wavelength conversion capacity in each node requires too many optical–electrical–optical (OEO) ports inevitably. To solve theses problems, waveband switching and intra-band wavelength conversion are proposed. By integrating traffic grooming and waveband switching, this paper devises a new multi-granularity traffic grooming mechanism with the function of intra-band wavelength conversion. Based on the proposed mechanism and integrated grooming policy (IGP), a new heuristic routing algorithm called multi-granularity traffic grooming based on integrated auxiliary graph (MGIAG) is also proposed since the traffic grooming problem is NP-hard. Simulation results show that, compared to traditional integrated grooming algorithm (IGA), MGIAG can save more ports and obtain lower blocking probability. Compared to traditional single-hop traffic grooming algorithm (SHA), lower blocking probability and more savings in transmitting ports can be achieved by multi-hop grooming in MGIAG and IGA although they consume more OEO ports.

Loss Differentiation in OBS Networks With Limited or No Wavelength Conversion

Quality of Service differentiation is an open research issue in optical burst switching (OBS) networks. Most proposals assume full wavelength-conversion, but wavelength converters are still very complex and expensive, and accordingly limited and no wavelength conversion OBS networks are likely to be the most common scenarios. In this paper, we define and analyze the QoS Multiple Wavelength Simultaneous Transmission technique (QoS-MWST), a novel method for providing loss differentiation in OBS networks with limited or no wavelength-conversion capability. In QoS-MWST, multiple copies of each burst are simultaneously sent on different wavelengths, so as to increase the chances of data delivery, and loss differentiation is achieved by properly sending more copies of the higher-priority bursts. Through analysis and extensive simulation experiments, we demonstrate that QoS-MWST can provide loss differentiation in OBS networks without full wavelength-conversion capability more efficiently than other differentiation techniques proposed in the literature.

On burst rescheduling in OBS networks with partial wavelength conversion capability

The core nodes in an optical burst switching (OBS) network are normally equipped with wavelength converters (WCs) to reduce the burst loss probability. Since WCs are expensive and still immature technologically, it is desirable to reduce the number of WCs in the network and to have partial wavelength conversion capability at the core nodes. Nevertheless, a majority of algorithms in the literature are proposed under the full wavelength conversion assumption. As a result, they do not consider the burst loss caused by insufficient WCs, i.e., bursts dropped due to the unavailability of free WCs to convert them to unused wavelengths. In this paper, we demonstrate how to use burst rescheduling to decrease the burst loss due to insufficient WCs and hence cut down on the overall burst loss probability in OBS networks. Two burst rescheduling algorithms are proposed. Their effectiveness in reducing the overall burst loss probability is verified through simulation experiments.

Pre-planned optical burst switched routing strategies considering the streamline effect

Optical burst switching is a promising paradigm for the next IP over optical network backbones. However, due to its bufferless nature, it can be highly affected by burst contention. Several methods have been proposed to address this problem, most of them without considering a phenomenon unique to optical burst switched networks called streamline effect. Most of the reported studies also assume the existence of total wavelength conversion capacity on all nodes, presently a very expensive and somewhat unrealistic configuration, and additionally, the contention resolution schemes adopted increase in the complexity of the core nodes, hampering scalability. In this study, we present a traffic engineering approach for path selection with the objective of minimizing the contention considering the streamline effect and using only topological information. The main idea is to balance the traffic across the network in order to prevent congestion while keeping simple the architecture of the core nodes and without incurring into link state dissemination penalties. We propose and evaluate the path selection strategies in both networks with full wavelength conversion capability and networks with imposed wavelength continuity constraint. Results show that our strategies can outperform the traditionally used shortest path routing.

Adaptive alternate routing in WDM networks and its performance tradeoffs in the presence of wavelength converters

Routing in wavelength-routed all-optical WDM networks has received much attention in the past decade, for which fixed and dynamic routing methods have been proposed. Taking into account the observation that wavelength-routed all-optical WDM networks are similar to circuit-switched voice networks, except with regard to wavelength conversion, we propose an adaptive alternate routing (AAR) scheme for wavelength-routed all-optical WDM networks. A major benefit of AAR is that it can operate and adapt without requiring an exchange of network status, i.e., it is an information-less adaptive routing scheme. The scope of this work is to understand this scheme in its own right since no other dynamic routing schemes are known to have the information-less property. In this paper, we conduct a systematic study of AAR with regard to factors such as the number of converters, load conditions, traffic patterns, network topologies, and the number of alternate paths considered. We observe that the routing scheme with multiple alternate routes provides more gain at a lower load instead of requiring any nodes to be equipped with wavelength converters. On the other hand, the availability of wavelength converters at some nodes, along with adaptive routing, is beneficial at a moderate to high load without requiring all nodes to be equipped with wavelength converters. We also observed that a small number of alternate routes considered in a network without wavelength converters gives a much better performance than a network with full wavelength converters and fewer alternate routes. Throughout this study, we observed that the proposed adaptive alternate routing scheme adapts well to the network traffic condition.