Photonic Network Communications

Ethernet-over-SONET/SDH (EoS) is a popular approach for interconnecting geographically distant Ethernet segments using a SONET/SDH transport infrastructure. It typically uses virtual concatenation (VC) for dynamic bandwidth management. The aggregate SONET/SDH bandwidth for a given EoS connection is obtained by “concatenating” a number of equal-capacity virtual channels. Together, these virtual channels form a virtually concatenated group (VCG). In this article, we introduce a new concatenation technique, referred to as cross-virtual concatenation (CVC), which involves the concatenation of virtual channels of heterogeneous capacities. We show that CVC can be implemented through a simple upgrade at the end node, thus utilizing the existing legacy SDH infrastructure. By employing CVC for EoS systems, we show that the SDH bandwidth can be harvested more efficiently than in conventional VC. We consider two problems associated with routing CVC connections: the connection establishment problem and the connection upgrade problem. The goal of the first problem is to compute a set of paths between two EoS end systems such that a total bandwidth demand and a constraint on the differential delay between the paths are satisfied. Among all feasible sets, the one that consumes the least amount of network bandwidth is selected. For this problem, we develop an integer linear program (ILP) and an efficient algorithm based on the sliding-window approach. For the connection upgrade problem, the goal is to augment an existing set of paths so as to increase the aggregate bandwidth, while continue to meet the differential-delay constraint. We model this problem as a flow-maximization problem with a constraint on the delay of the virtual channels with positive flow. We then consider the problem of path selection under imprecise network state information. Simulations are conducted to demonstrate the advantages of employing CVC and to evaluate the performance of the proposed algorithms.

Optical burst switching (OBS) is a promising switching paradigm for building the next generation optical internet. The proportional differentiation model is very convenient for network operators to quantitatively adjust the quality differentiation among service classes. To provide proportional differentiated services for OBS networks, a proportional differentiation scheme based on batch scheduling is proposed in this article. The scheme adopts the batch scheduling idea to reserve data channel resources for a batch of data bursts. It helps to decrease burst dropping probability. When some data bursts are unsuccessfully scheduled, a preemption method is used to keep a proportional burst dropping probability among service classes according to the expected burst dropping probability equations given by the proportional differentiation model. The scheme has low computational complexity. Simulation results show that the scheme can provide proportional differentiated services and efficiently decrease the burst dropping probability.

The article addresses a simulation-based optimization approach for allocation of ADMs in WDM optical networks with stochastic dynamic traffic. Since ADMs are expensive, it is desirable that if each node in WDM optical networks can use a minimum number of ADMs to achieve a near-ideal performance. In this article, first, the utilization statistics of ADMs are gathered by simulation. Then, ADMs are allocated based on the utilization statistics. In this respect, a simple sorting mechanism is used. The distinguished feature of the proposed approach is that it shows the way to allocate ADMs at the nodes of WDM optical networks with stochastic dynamic traffic. The experimental results ensure that the proposed approach can solve the problem of allocating ADMs in practical WDM optical networks considering stochastic dynamic traffic.

Most research to date in survivable optical network design and operation, focused on the failure of a single component such as a link or a node. A double-link failure model in which any two links in the network may fail in an arbitrary order was proposed recently in literature [1]. Three loop-back methods of recovering from double-link failures were also presented. The basic idea behind these methods is to pre-compute two backup paths for each link on the primary paths and reserve resources on these paths. Compared to protection methods for single-link failure model, the protection methods for double-link failure model require much more spare capacity. Reserving dedicated resources on every backup path at the time of establishing primary path itself would consume excessive resources. Moreover, it may not be possible to allocate dedicated resources on each of two backup paths around each link, due to the wavelength continuous constraint. In M. Sridharan et al., [2,3] we captured the various operational phases in survivable WDM networks as a single integer programming based (ILP) optimization problem. In this work, we extend our optimization framework to include double-link failures. We use the double-link failure recovery methods available in literature, employ backup multiplexing schemes to optimize capacity utilization, and provide 100% protection guarantee for double-link failure recovery. We develop rules to identify scenarios when capacity sharing among interacting demand sets is possible. Our results indicate that for the double-link failure recovery methods, the shared-link protection scheme provides 10–15% savings in capacity utilization over the dedicated link protection scheme which reserves dedicated capacity on two backup paths for each link. We provide a way of adapting the heuristic based double-link failure recovery methods into a mathematical framework, and use techniques to improve wavelength utilization for optimal capacity usage.

In an optical burst switching (OBS) network, the blocking time, representing the time interval during which the channel is occupied for a given class of incoming burst, is a key metric for performance evaluation and traffic shaping. In this paper, we study a horizon-based single-channel multi-class OBS node, for which the multiple traffic classes are differentiated using different offset time of each class. By assuming Poisson burst arrivals and phase-type distributed burst lengths and using the theory of Multi-layer stochastic fluid model, we obtain the Erlangian approximation for the finite time probability of the blocking time for a given class of burst in an OBS node. We further propose an explicit algorithm and procedure to calculate the Erlangian approximation. Numerical results are provided to illustrate the accuracy and the speed of convergence of the proposed method.

This paper reports on a novel strategy and related algorithm for realizing dynamic routing and grooming into wavelengths of data flows (label switched paths, LSPs) in new generation optical networks based on generalized MPLS (GMPLS). The method allows arbitrary granularities of LSPs. The new generation network is modeled as a multi-layer network consisting of an IP/MPLS layer and an optical layer. In particular, the proposed solution adopts a dynamic routing algorithm based on the Dijkstra algorithm, that makes use of a weight system, integrated with a suitable method for grooming LSPs into wavelengths based on the packing criterion, thus harmonizing the features of MPLS packet flows whose bandwidth vary in a continuous range of values, with the optical world, where the wavelength bandwidth ranges according to discrete values. The weight system is based on the concepts of least resistance routing that allows to evenly distribute the traffic at the MPLS layer, while packing improves the use of optical resources by favoring more filled wavelengths with respect to the emptier ones. To assess the validity of the proposed solution a simulation model has been realized. The results obtained by simulation show that the packing criterion allows reducing the refused bandwidth from two down to about four times, for a network load of 70% and 55%, respectively, when compared with the alternative method named spreading. The dependence of the proposed solution on bandwidth granularity has been also investigated. Moreover, in order to demonstrate the superior performance of the proposed routing solution, a comparison between the proposed strategy with relevant solutions known in the literature, based on either a single or multi-layer approach, is also reported. In order to perform the comparison, all the reference routing solutions that have been considered adopt the packing method for LSP grooming into the lightpaths. The results show that our solution outperforms the others in terms of amount of traffic that can be on-line accommodated. For instance, assuming a blocking probability of 10−3, the proposed solution is able to further reduce the refused bandwidth of the best routing algorithm considered in the analysis by a factor of three times, thanks to the knowledge of optical resource availability.

This article presents a resilient star-ring optical broadcast-and-select network with a centralized multi-carrier light source (C-MCLS). It consists of a star part network and a ring part network. Optical carriers generated by the C-MCLS are broadcast to all network nodes, which select and utilize them for data transmission. Optical carrier distribution as well as data transmission and receiving are performed in the star part network. The ring part network is for fiber failure recovery. The network resilience property enables the design of a fast distributed failure recovery scheme to deal with single and multiple fiber failures. We introduce a fiber connection automatic protection switching (FC-APS) architecture that only consists of optical couplers and 1 × 2 optical switches for each network node. Based on the FC-APS architecture, we design a distributed failure recovery scheme to recover the carriers and data affected by fiber failures. The fiber failure detection and failure recovery operations are performed by each network node independently only using its local information. We evaluate the recovery time of the distributed failure recovery scheme compared with that of the centralized one. Numerical results show that the distributed scheme greatly reduces the recovery time compared to the centralized configuration in the recoveries of both single and multiple fiber failures. Optical power loss analysis and compensation of the recovery routes in the distributed scheme are also presented. We show the required number of optical amplifiers for the longest recovery route in the distributed scheme under different numbers of network nodes and fiber span lengths.

Much work has focused on traffic grooming in SONET/WDM ring networks. Previous work has considered many aspects of traffic grooming, including minimizing the number of ADMs, minimizing the number of wavelengths, considering different traffic models, using different network architectures, incorporating switching capability and so on. In this work, we study traffic grooming in unidirectional ring networks with no switching capability under both uniform traffic and non-uniform traffic models to reduce electronic multiplexing costs. Based on the clustering notion, we derive a general and tighter lower bound for the number of ADMs required in traffic grooming under the uniform all-to-all traffic model. This bound reduces to special cases obtained in previous work. We also derive general, tighter, and closed form lower bounds for the number of ADMs required under two non-uniform traffic models: the distance-dependent traffic model and the non-uniform symmetric traffic model. Cost-effective multi-phase algorithms that exploit traffic characteristics are then designed and studied to efficiently groom traffic streams under different traffic models. Our numerical and simulation results show that the proposed multi-phase algorithms outperform existing traffic grooming algorithms by using a fewer number of ADMs. Our algorithms in several cases also achieve the lower bounds derived.

The next-generation passive optical networks (NG-PONs) are expected to offer very high data rate to large number of users. Long-reach passive optical network (LR-PON) is considered to be one of the most promising solutions for NG-PONs. Since providing full protection (i.e., 100 % reliability) to each user in LR-PON is complex and cost-prohibitive, we propose in this study a novel heuristic scheme against single shared-risk link group (SRLG) failure to ensure certain degree of reliability (as determined by the network operator) to the users. In the proposed scheme (referred to as clustering-based multi-hop protection or CMHP scheme), we allocate residual capacity of backup optical network units (ONUs) among the ONUs that require protection by using bypass-based multi-hop traffic transmission strategy through backup fibers. CMHP scheme reduces the total length of backup fibers to be deployed between the ONUs (that require protection) and the respective backup ONUs through sharing of the backup fibers. In this study, we evaluate the total required length of backup fiber for a given network setting and different reliability requirements (viz. 75, 85 and 95 %). With the help of exhaustive simulations, we show that CMHP scheme significantly reduces the total length of backup fiber with reference to existing scheme to protect against single SRLG failure. We also explore a heuristic scheme referred to as clustering-based multi-hop protection with consideration of street layout (i.e., CMHP-SL) to implement CMHP scheme in practical scenario with due consideration of the street layout. CMHP-SL scheme provides protection to ONUs following a cost-efficient approach based on the existing fiber infrastructure in the distribution section.