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Existing analytical models (EAMs) are used to find the quality of service of optical networks with wavelength division multiplexing (WDM). However, the convergence of EAMs decreases with an increase in traffic load and the numbers of wavelength (w) channels. EAMs are used to compute approximated numerical values of blocking probabilities (BPs) which are based on an iterative approach. There are cases in EAMs when numerical BP values do not converge to a single point after numerous iterations. In this paper, the converge issues of EAMs have been addressed by considering a recursive approximation based on iterative approach with the convergence criteria which is called an advance approximated BP model (AABPM). The accuracy of the AABPM for WDM optical networks is examined by comparing with an EAM as well as simulation results which shows that AABPM converges to give similar approximated numerical values with less convergence time. [ABSTRACT FROM AUTHOR]

Elastic optical networking is a potential candidate to support dynamic traffic with heterogeneous data rates and variable bandwidth requirements with the support of the optical orthogonal frequency division multiplexing technology (OOFDM). During the dynamic network operation, lightpath arrives and departs frequently and the network status updates accordingly. Fixed routing and alternate routing algorithms do not tune according to the current network status which are computed offline. Therefore, offline algorithms greedily use resources with an objective to compute shortest possible paths and results in high blocking probability during dynamic network operation. In this paper, adaptive routing algorithms are proposed for shortest path routing as well as alternate path routing which make routing decision based on the maximum idle frequency slots (FS) available on different paths. The proposed algorithms select an underutilized path between different choices with maximum idle FS and efficiently avoids utilizing a congested path. The proposed routing algorithms are compared with offline routing algorithms as well as an existing adaptive routing algorithm in different network scenarios. It has been shown that the proposed algorithms efficiently improve network performance in terms of FS utilization and blocking probability during dynamic network operation. [ABSTRACT FROM AUTHOR]

Highlights • A hybrid routing scheme is proposed for routing in EON. • An optimizaton model is presented with heterogeneous bandwidth demands. • The proposed model maintains a minimum level of congestion on all links. • The proposed model is integrated with the spectrum allocation subproblem with the continuity and contiguity constraints. • The proposed RSA scheme helps to efficiently reduce network blocking probabilities. Abstract Elastic optical networks (EON) has received intensive research attraction due to its agile spectrum management in the underlying optical backbone infrastructure whose channels can be allocated on variable spectrum width. In this paper, a hybrid scheme is proposed for routing and spectrum allocation (RSA) in EON. An optimization formulation is modeled which takes into account the elastic bandwidth characteristics of optical paths as well as maintains a threshold congestion level on all links. The goal of the proposed model is to minimize the cost of using the network links which results in the minimum cost paths between node pairs. The proposed optimization model is solved offline in the initial stage to obtain routing information which is utilized for online traffic in the second stage. The proposed model is integrated with the spectrum allocation subproblem with the continuity and contiguity constraints. The computational time of the optimization model is shown to be in (time unit) seconds for different networks which is an acceptable time to obtain routing information in the initial stage. The proposed RSA scheme helps to efficiently reduce network blocking probabilities in different network scenarios as the optimization model manages to route traffic load to the underutilized links when the quality of service of lightpaths on the overutilized links meet the desired threshold congestion level. [ABSTRACT FROM AUTHOR]

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results. [ABSTRACT FROM AUTHOR]

Until now, optimization problems have been considered for routing and resource allocation of static traffic. In this paper, we formulate an integer optimization problem which jointly considers routing and dimensioning in WDM networks in the pre-optimization stage. Since the integer optimization problems are computationally difficult to solve, therefore the integer constraints of the integer optimization problem are relaxed using LP relaxation in the pre-optimization stage. The LP relaxation technique computationally makes the optimization problem to give solutions in short duration of time for various networks. The optimal results obtained from the pre-optimization stage are rounded to integer values in the post-optimization stage which give the numbers of wavelength channels. The solutions obtained from the pre-optimization stage are utilized jointly for routing and dimensioning in the post-optimization stage for dynamic traffic. The link blocking probabilities have been considered as a merit of quality of service for dynamic traffic in different WDM networks. It has been shown through simulations that the proposed two stage optimal routing and dimensioning technique outperforms existing routing and undimensioning WDM networks in various network scenarios. [ABSTRACT FROM AUTHOR]

Currently, analytical models are used to compute approximate blocking probabilities in opaque and all-optical WDM networks with the homogeneous link capacities. Existing analytical models can also be extended to opaque WDM networking with heterogeneous link capacities due to the wavelength conversion at each switch node. However, existing analytical models cannot be utilized for all-optical WDM networking with heterogeneous structure of link capacities due to the wavelength continuity constraint and unequal numbers of wavelength channels on different links. In this work, a mathematical model is extended for computing approximate network blocking probabilities in heterogeneous all-optical WDM networks in which the path blocking is dominated by the link along the path with fewer number of wavelength channels. A wavelength assignment scheme is also proposed for dynamic traffic, termed as last-fit-first wavelength assignment, in which a wavelength channel with maximum index is assigned first to a lightpath request. Due to heterogeneous structure of link capacities and the wavelength continuity constraint, the wavelength channels with maximum indexes are utilized for minimum hop routes. Similarly, the wavelength channels with minimum indexes are utilized for multi-hop routes between source and destination pairs. The proposed scheme has lower blocking probability values compared to the existing heuristic for wavelength assignments. Finally, numerical results are computed in different network scenarios which are approximately equal to values obtained from simulations. [ABSTRACT FROM AUTHOR]

• A routing algorithm is proposed for elastic optical networks with mixed line rates. • Routing decisions are initially made based on the modulation scheme with high data rates. • A route with maximum idle FS is preferred in case of multiple routes with same modulation. • If a tie occurs further, routing decision is made based on minimum hop count. • The proposed algorithm considers the first-last-mixed-fit spectrum allocation. • The proposed algorithm minimizes fragmentation and increases path contiguity. In this work, an adaptive routing, modulation, and spectrum allocation (RMSA) scheme is proposed for dynamic traffic in elastic optical networks (EON) which allocates resources based on EON characteristics during the RMSA decision process. The proposed scheme selects a route from the set of available paths which efficiently utilizes available resources on all links during network operation stage. Initially, routes are determined from the set of available paths based on a feasible modulation scheme with higher data rates and requiring minimum contiguous frequency slots (FSs) as well as satisfying optical reach of the modulated signal. During the operation stage, routes between end pairs are determined from these preselected paths based on maximum idle FSs on a path. This increases resources utilization on the underutilized routes with maximum path contiguity and having minimum fragmentation. In case of tie among routes with similar numbers of maximum idle FSs, the proposed algorithm selects a path with minimum numbers of hops. Finally, the proposed routing algorithm is integrated with the proposed first-last-mixed fit spectrum allocation scheme which increases average path contiguity and reduces average path external fragmentation for connection requests with mixed line rates requiring contiguous FSs. Simulation results show that the proposed RMSA scheme efficiently reduces the amount of blocking probability, reduces average path external fragmentation, increases average resources utilization, and increases average path contiguity in different network scenarios compared to the existing minimum hop based routing and k-distance adaptive paths (KDAP) routing schemes. [ABSTRACT FROM AUTHOR]

The intelligent driver (ID) model characterizes traffic behavior with a constant acceleration exponent and does not follow traffic physics. This results in unrealistic traffic behavior. In this paper, a new microscopic heterogeneous traffic flow model is proposed which improves the performance of the ID model. The forward and lateral distance headways are used to characterize traffic behavior. The stability of the ID and proposed models is examined over a 1000 m circular road with a traffic disturbance after 30 s. The results obtained show that the proposed model is more stable than the ID model. The performance of the proposed and ID models is evaluated over an 1800 m circular road for 150 s with a platoon of 51 vehicles. Results are presented which indicate that traffic evolves realistically with the proposed model. This is because it is based on the lateral distance headway. [ABSTRACT FROM AUTHOR]

This paper introduces a novel free space optics (FSO) communication system for future-generation high-speed networks. The proposed system integrates orbital angular momentum (OAM) modes with an optical code division multiple access (OCDMA) technique. Two OAM beams are used ( L G 0 , 0 and L G 0 , 10 ), each of which is used for transmitting three independent channels. Each channel is assigned by fixed right shift (FRS) codes and carries 10 Gbps of information data. The performance of the proposed model is evaluated under different foggy and dust storm conditions. Furthermore, the performance of two cities with different geographical locations, Alexandria city in Egypt and Srinagar city in India, is investigated to demonstrate its ability to be implemented in future generations. Bit error rate (BER), eye diagrams, received optical power (ROP), and channel capacity are used for studying the performance of the proposed system. The observed simulation results show successful transmission of 60 Gbps overall capacity with the longest propagation FSO range for Alexandria city, which is 1400 m. Because dust storms have a large attenuation when compared to different foggy conditions, the proposed model had the shortest propagation range of 315 m under low dust (LD), 105 m under moderate dust (MD), and 40 m under heavy dust (HD). Furthermore, the cloudy weather conditions that affect Srinagar city, which is considered a hilly area, make our suggested model achieve 1000 m. [ABSTRACT FROM AUTHOR]

Adaptability of an effective access network in optical code division multiple access domain requires an efficient coding scheme which has the abilitiy to provide required communication capacity in terms of cardinality, reach, and data rates. In this paper, an extensive study and investigation has been carried out for adaptability study of a well-known coding scheme diagonal eigenvalue unity (DEU) code at various date rates in passive optical network (PON) environment. DEU code design is based on Jordan block matrix with ideal in-phase cross correlation (IPCC) properties. The numerical and simulation results show the ability of DEU code in supporting synchronized transmissions at different data rates that suits triple play services of video, audio and data (VAD). An algorithm is developed to determine the required chip duration that matches a particular service. It shows that data rate is more influential than code length on pulse duration especially for video applications. In support of the proposed algorithm, 5 Gb/s, 2.5 Gb/s, and 1.25 Gb/s data rate transmissions have been validated for various simultaneous users. In addition, a Poisson's distribution analysis is carried out aiming to study different bit rate scenarios with ad hoc population network. Results have concluded that higher value of average rate of simultaneous users (σ) is preferable for low data rate whereas the lower value of σ is suitable to the higher data rates in accordance with network population. In particular, for video streaming, the traffic running in a continuous fashion requires the highest transmission priority and small value of σ. [ABSTRACT FROM AUTHOR]