A QoS-aware wavelength assignment scheme for optical networks

Dispersion in fiber optic is wavelength dependent and it degrades the quality of service (QoS) in an optical network. Although use of dispersion compensating fiber reduces the effects of dispersion but it is very costly. In this paper, we propose a QoS-aware wavelength assignment (QWA) scheme to improve the quality of service in an optical network by reducing the overall dispersion in the network. In this scheme, the connection requests with longer lightpath are assigned the wavelengths having lesser dispersion and the wavelengths having higher dispersion are assigned to the lightpaths with shorter distance. The lightpaths are computed using alternate path routing to achieve the lower blocking probability. The performance analysis of QWA scheme is done in terms of total dispersion using step-index fiber (SIF). Results of our experiments show that QWA scheme outperforms conventional wavelength assignment scheme based on First-Fit method (WAFF).     

Distributed control based routing and wavelength assignment strategy for WDM optical networks

Wavelength-division-multiplexing (WDM) is emerging as the dominant technology for the next generation optical networks. The control strategy can be either centralized or distributed. In centralized control, there is a central controller to keep track of the state of the network. It is also responsible for selecting the path for data transmission. Most of the work done in this field is based on centralized control. For large networks, distributed control is preferred over centralized control because of low control overhead. Distributed control strategy requires exchange of control messages among nodes. The distributed control generally results in the possibility of resource reservation conflicts among simultaneous path establishments and poor resource utilization. In this paper, we have proposed one distributed control based routing and wavelength assignment strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources.     

Routing and wavelength assignment algorithms for translucent optical networks

Due to transmission impairments, optical regeneration is needed to extend the length of a lightpath beyond its transparent length. Spare transmitter (Tx) and receiver (Rx) modules in an optical network node can be used for optical regeneration. A Max-spare algorithm for locating the regeneration nodes for a lightpath is proposed and compared with a Greedy algorithm in conjunction with two routing algorithms, namely, wavelength weighted (WW) and length weighted (LW) routing algorithms. Through simulation we find that significant number of lightpaths that cannot be established due to the violation of transparent length can be established if the regeneration algorithm is used to select transit nodes that have spare Tx and Rx for 3R regeneration. The translucent optical network with limited number of transceivers can still perform close to a transparent optical network with full set of transceivers. We find that for the same routing algorithm, the Max-spare algorithm yields better results than the Greedy algorithm. In addition; for the same regeneration nodes selection algorithm, the WW algorithm has better performance than the LW algorithm.     

Routing and wavelength assignment algorithms for multiclass WDM optical networks

In this paper dynamic routing and wavelength assignment strategies have been proposed for multiclass WDM optical networks. Multiclass optical networks provide multiple classes of services to the subscriber according to the requirement, which in turn increase operational profitability. Each class of service could be characterized by parameters like number of wavelengths, expected call holding time and average arrival rate of request. The proposed strategies have been analyzed and compared with existing strategies on the basis of blocking probabilities for multiclass traffic scenarios. Simulation results on different network topologies demonstrate that the performance of proposed strategies “Fixed shortest/alternate shortest path routing with wavelength reservation (FSASWR)” and “Fixed alternate shortest path routing with least priority wavelength assignment (FASPL)” are much better as compared to existing strategies. Proposed strategies minimize blocking probability of the multiclass network using limited number of wavelengths.     

Wavelength assignment algorithms for WDM optical networks

In this paper, we have proposed an efficient wavelength assignment algorithm for dynamic provisioning of lightpath. This proposed algorithm is based on most-used wavelength assignment algorithm. We have also suggested a mathematical model for WDM optical networks for minimization of blocking probability. The results of proposed algorithm and suggested model are then compared with the conventional wavelength assignment algorithms such as first-fit, best-fit, random and most-used wavelength assignment algorithms. These proposed approaches are very effective for the minimization of blocking probability of optical WDM networks.     

WDM全光网络中一种分布式路由及波长分配协议

在全光网络中,光信号在全光域内传输,避免了光-电转换带来的延迟,因此全光网支持高数据率传输并提供巨大的网络容量。WDM(波分多路复用)技术的采用使得高速光传输线路与低速终端处理设备之间能够相互兼容。探讨了WDM全光网中的路由及波长分配问题,提出了一种用于WDM网络中的分布式路由及波长分配协议,具有开销小、阻塞率低以及良好的可扩展性,是一种比较实用的RWA协议。     

A Heuristic algorithm for reducing wavelength number of optical WDM networks

This paper proposes a Heuristic algorithm in order to reduce the total number of wavelengths required to accommodate light-paths in a WDM networks with static traffic loading. Proposed algorithm is compared with Dijkstra's algorithm for average light-path length and wavelength number of network. To see the efficiency of this 01algorithm new parameter, reduced wavelength cost (RC_X) has been defined.     

Routing and wavelength assignment in WDM networks with dynamic link weight assignment

We consider the routing and wavelength assignment problem on wavelength division multiplexing networks without wavelength conversion. When the physical network and required connections are given, routing and wavelength assignment (RWA) is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In wavelength division multiplexing (WDM) optical networks, there is need to maximize the number of connections established and to minimize the blocking probability using limited resources. In this paper, we have proposed three dynamic link weight assignment strategies that change the link weight according to the traffic. The performance of the existing trend and the proposed strategies is shown in terms of blocking probability. The simulation results show that all the proposed strategies perform better than the existing trend.     

A risk-sharing multicast recovery scheme based on redundant trees in optical networks

Resilient and efficient multipoint mechanisms are required in optical networks. In this study, we propose a risk-sharing primary tree selection algorithm to enhance the redundant tree recovery method in multipoint optical networks. The mechanism not only can ensure the minimum hop distance from the source to every destination, but also can make nodes in the network share the risk of failure and degradation by averaging the number of messages triggered. Simulations demonstrate that the proposed mechanism ensures a better network environment after failure or degradation of multipoint optical networks.     

Routing and wavelength assignment in wavelength-routed all-optical WDM networks

In this paper, low-complexity mathematical model has been developed which is used for the calculation of the blocking probability of network and this model does not require any simulation statistics. The implementation of the model proposed has less complexity and the computation used in this model is quite efficient. The routing algorithm has also been proposed in this paper depending upon the proposed model, which is very efficient in calculation and minimization of the blocking probability. This algorithm suggests an optimum path as a solution to routing problem. The wavelength assignment technique has also been suggested in this paper to minimize the blocking probability. The proposed model and algorithms can be implemented on different network topologies. Furthermore, the model, routing algorithm and wavelength assignment technique is also used to evaluate the blocking performance of NSFNet and EUPAN Network topology and hence used to improve its performance on the basis of the blocking probability.     

Performance analysis of topologies for optical wavelength convertible networks

An architecture of wavelength converters shared per-node wavelength cross-connects is proposed to function the optical node in simulation. And first-fit wavelength allocation algorithm and Dijkstra shortest path routing algorithm are used. It is shown that star topology performs the best on blocking probability, average hop count and average packet delay, but it is unfavorable on link utilization. Furthermore, wavelength conversion is not ideal for the star topology. However, the ring topology network is the cost-optimal one if the appropriate wavelength conversion capability in network is to be considered.     

A novel scheme based on minimum delay at the edges for optical burst switching networks

This paper proposes a novel scheme based on minimum delay at the edges (MDE) for optical burst switching (OBS) networks. This scheme is designed to overcome the long delay at the edge nodes of OBS networks. The MDE scheme features simultaneous burst assembly, channel scheduling, and pre-transmission of control packet. It also features estimated setup and explicit release (ESXR) signaling protocol. The MDE scheme can minimize the delay at the edge nodes for data packets, and improve the end-to-end latency performance for OBS networks. In addition, comparing with the conventional scheme, the performances of the MDE scheme are analyzed in this paper.     

Static and dynamic routing and wavelength assignment algorithms for future transport networks

In this paper, two static and three dynamic routing algorithms have been proposed and compared to some of the existing algorithms on the basis of blocking probability. The two proposed static routing and wavelength assignment (RWA) algorithms reduce the blocking probability to maximize the utilization of network. For dynamic algorithms, first a model with no weights assignments is presented and then three algorithms are proposed and analysed with weight assignment resulting in reduction of blocking probability. All these algorithms are analysed and compared with four wavelength assignment schemes which are first-fit, random, most used and least used. It is shown that our proposed static algorithms give the best performance for first-fit wavelength assignment and most used wavelength assignment strategies with reduced complexity. For least used wavelength assignment and random wavelength assignment, 1 fixed and 2 alternate routing algorithm gives the lowest blocking probability. For dynamic routing, it has been shown that our proposed algorithm “less weight to maximum empty and nearest” gives the least blocking probability as compared to the other dynamic routing algorithms for random, most used and least used wavelength assignment strategies.     

A novel differentiated services supporting scheme for optical burst switched networks

In this letter, we analyze the drawback of tail-dropping contention resolution in optical burst switched networks. Once contention occurs, we adopt modified head-dropping policy to resolve contention. This policy drops the head of the contending burst only if the overlapping region of the two bursts is less than the whole contending burst size, otherwise drops the whole contending burst. In order to have a better support of differentiated service, a new burst assembly policy, namely, Priority-based proportional mixed burst assembly, is proposed. Simulation results show that the proposed scheme performs very well in terms of performance metrics such as the times of contention and packet loss probability.     

Comparison of optical network topologies for wavelength division multiplexed transport networks

In this paper, the various network topologies comprising of various nodes have been investigated and compared. The signal is analyzed as it passes through each node in each of the network topology. For the ring topology, it is shown that there is no appreciable signal degradation in the ring network. It is seen that there is increase in Quality factor i.e. signal keeps on improving as it passes through the successive nodes. For the bus topology, the quality of signal goes on decreasing with increase in the number of nodes and the power penalty goes on increasing. For the star topology, it is observed that received power values of each node at a same distance from the hub are same and the performance is same. For the tree topology, it is observed that the performance of the optical tree is almost identical to the performance of ring topology, as signal quality is improved as it passes through the successive nodes of the hierarchy but the overall length of each segment is limited by the type of cabling used and if the backbone line breaks, the entire segment goes down.     

A heuristic approach to automated molecular line assignment

A first investigation on the feasibility of automated molecular line assignment is presented. Dense rovibrational molecular spectra are normally assigned by strongly interactive computer methods, ranging from commercial spreadsheets to dedicated programs, like Loomis-Wood or Ritz. While a general-purpose, fully automated assignment procedure seems to be out of reach for the near future, we show that a thorough investigation of the problem can lead to new, more efficient and less interactive methods, at least in reasonably favorable conditions. Interesting suggestions are provided by some modern “heuristic” problem-solving algorithms, which mimic natural processes. As a first step, we have developed a “transgenic-evolutionary” algorithm, which has successfully assigned artificial spectra of up to almost 3500 lines. We discuss also its performance on an experimental, but “filtered,” methanol spectrum. Possible future improvements and developments of this method, as well as its limits, are discussed.     

Analysis of reconfigurable multi-channel wavelength add drop multiplexer for intelligent optical networks

This paper presents design of an electro-optically tunable polymer multi-channel wavelength add drop multiplexer (WADM). The proposed WADM with trapezoidal waveguide geometry and poled electro-optical polymer material in the waveguide cores enables the wavelength tuning speed of WADM as 7.5 ps at the resonance wavelength of 1550 nm and coupling length of 1.5 mm. The device can be electro-optically tuned to add/drop multiple channels. Transmission spectra of the device with varying device parameters are simulated. The proposed WADM with high speed, small size and varying tuning capability makes this device, an important element in faster provisioning and routing of light paths in intelligent optical network.     

Survivable routing and wavelength assignment algorithm for multiple link failures in wavelength-routed all-optical WDM networks

In this paper, we have investigated the problem of enhancing multiple-fault restorability in the path protected wavelength-routed all-optical WDM networks. The system architecture considered is circuit-switched with dynamic arrival of session requests. We have proposed a mechanism, which is used to combat multiple link failures. A survivable routing and wavelength assignment algorithm has been proposed which is very efficient for the networks having multiple failures. This algorithm deals with the optical networks with multiple faults and is effective for the varying load applied to nodes. This algorithm works well for the load applied to the nodes varying from low to high.     

Fault-tolerant routing and wavelength assignment algorithm for multiple link failures in wavelength-routed all-optical WDM networks

In this paper, we investigate the problem of enhancing multiple-fault restorability in the path protected wavelength-routed all-optical WDM networks. The system architecture considered is circuit-switched with dynamic arrival of session requests. We propose a mechanism, which is used to combat multiple link failures. A routing and wavelength assignment algorithm has been proposed with the name of fault-tolerant routing and wavelength assignment algorithm. The comparison of this algorithm has also been made with the best-fit and first-fit algorithms. This algorithm deals with the optical networks with multiple faults and is effective for the varying load applied to nodes. This algorithm works well for the load applied to the nodes varying from low to high.     

Cyclic polling-based dynamic wavelength and bandwidth allocation in wavelength division multiplexing passive optical networks

Cyclic polling-based dynamic wavelength and bandwidth allocation algorithm supporting differentiated classes of services in wavelength division multiplexing （WDM） passive optical networks （PONs） is proposed. In this algorithm, the optical line terminal （OLT） polls for optical network unit （ONU） requests to transmit data in a cyclic manner. Services are categorized into three classes： expedited forward （EF） priority, assured forwarding （AF） priority, and best effort （BE） priority. The OLT assigns bandwidth for different priorities with different strategies. Simulation results show that the proposed algorithm saves a lot of downstream bandwidth under low load and does not show the light-load penalty compared with the simultaneous and interleaved polling schemes.