All-optical networks with sparse wavelength conversion

Sparse wavelength conversion is essentially achieved for free in all-optical express networks by taking advantage of wavelength conversion at regeneration sites. As has been shown in numerous studies, sparse wavelength conversion is sufficient for achieving utilization levels close to those of networks with full wavelength conversion. We discussed qualitatively why this should be expected for all-optical express networks, and further demonstrated this using four carrier networks. Thus, the significant savings in capital and operating expenses and the fast-provisioning benefits of all-optical networks can be attained with very little loss of network efficiency.

In this paper, the importance of wavelength converter modules in all-optical networks is highlighted. Two types of wavelength converters are proposed, static and dynamic wavelength converters. A wavelength converter (also referred to as Frequency Transformer) converts the wavelength of the incoming optical signal to another wavelength in the wavelength spectrum. The goal of this work is to provide some insights into the effect of static versus dynamic wavelength conversion on the performance of optical networks based on Bidirectional de Bruijn (BdB) topology. We study how performance (in terms of blocking probability and the network load) depend on the number of wavelengths per optical link. We also evaluate performance of a given network employing both static and dynamic wavelength converters through simulation and present the simulation results. The motivation behind having static wavelength converters is the relatively low cost compared to dynamic wavelength converters. Also an Error-Correcting Routing Algorithm (ECRA) is proposed that makes use of static wavelength converters which is based on the principle of error-correcting routing.

We present a new analytical technique, based on the inclusion-exclusion principle from combinatorial mathematics, for the analysis of all-optical networks with no wavelength conversion and random wavelength assignment. We use this technique to propose two models of low complexity for analysing networks with arbitrary topologies and traffic patterns. The first model improves the current technique by Birman (1996) in that the complexity of calculation is independent of hop-length and scales only with the capacity of the link as against that of Birman's method which grows exponentially with hop-length. We then propose a new heuristic to account for wavelength correlation and show that the second model is accurate even for sparse networks. Our technique can also be extended to analyse fixed alternate and least loaded routing.

In this work, we propose a new distributed signaling scheme, within the GMPLS framework for establishing lightpaths in wavelength-routed networks with sparse wavelength conversion. Analytical models are developed to evaluate the performance of the proposed scheme. Theoretical and simulation results show that compared to the classic schemed designed primarily for networks with no wavelength conversion, the proposed signaling scheme can achieve much lower blocking probability.

This paper considers the problem of establishing dynamic lightpaths in WDM optical mesh networks employing shared-path protection with sparse wavelength conversion. Two mechanisms for routing and wavelength assignment are proposed for achieving an efficient use of the scarce converters. The NSFNET topology is used in a computer simulation experiment to assess the effectiveness of these mechanisms. Depending on the network load, a blocking probability improvement of 10?65% can be achieved.

In this paper, we propose and evaluate a new concept of traffic aggregation in wavelength-division multiplexing (WDM) optical networks that aims at eliminating both the bandwidth underutilization and the scalability concerns that are typical of all-optical wavelength-routed networks. Our objective is to reduce the network cost while preserving the benefits of all-optical wavelength-routed networks. In order to assess the efficiency of our proposal, all underlying network costs are compared. These costs include that of the transceivers and cross-connect ports required at node level, as well as the number of wavelengths. Our results show that the proposed aggregation technique can significantly reduce the network cost

Network performance is improved by performing wavelength conversions in an all‐optical network. However, performing wavelength conversions entirely by current wavelength conversion techniques is difficult. Although the network performance is improved by having multiple optical fibers on each link, the network cost is inevitably increased. In this paper we propose a layered graph method which can simply describe a routing/wavelength assigning problem of a network with a limited‐range wavelength conversion capability in which a link has multiple fibers, together with an algorithm for routing/wavelength assignment using a hierarchical graph. In addition, the effects of wavelength conversions and multiple fibers and the performance from the cost point of view are studied by simulation. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 92–101, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1165

A promising way to realise a high capacity optical network is to utilise the wavelength dimension for address assignment of the nodes. In order to obtain scalability in such networks the wavelengths have to be re-used [1], [2] to allow the number of nodes to be independent of the number of available wavelengths. The idea is to divide the network into segments with equal wavelength maps and to connect these segments via wavelength converters.

Most works about all-optical circuit-switched WDM networks considers a shortest path algorithm for fixed routing, like the Dijkstra’ algorithm. However, recently, two new algorithms, searching for better load balancing and presenting superior performance than Dijkstra´s when submitted to an uniform traffic load, were proposed, the Restricted Routing Technique (RRT) and the Best among the Shortest Routes - (BSR). This work evaluates the performance of these algorithms under a non-uniform traffic load. For each topology studied were observed specific characteristics of the impact of the non-uniform traffic load for each routing algorithm. Overall, performance evaluation results showed that the algorithm BSR achieves for all topologies studied superior performance in terms of blocking probability and fairness.

In this paper we study on-line wavelength assignment in wavelength-routed WDM networks under both unicast and multicast traffic. We assume nodes in the networks have wavelength conversion ability. Since wavelength converters are still expensive and difficult to implement, we consider the networks that have only a limited number of converters in each node, and the converters are shared by all input channels at the node. We consider how to set up connections in such networks using as few wavelength converters as possible. For unicast traffic, we first study the problem of setting up a lightpath on a given link path with minimum number of conversions, and give a new algorithm that solves it in O(tk) time, where t is the number of links on the path and k is the number of wavelengths per fiber, as compared to the best known existing algorithm that runs in at least O(t/sup 2/k) time. We also consider the case when nodes have different conversion priorities, and give an O(tk) time algorithm for setting up a lightpath on a given link path while converting wavelength at higher priority nodes only when necessary. We then generalize this technique to WDM networks with arbitrary topologies and present an algorithm that sets up an optimal lightpath network-wide in O(Nk + Lk) time by checking the state of the entire network, where N and L are the number of nodes and links in the network, respectively. For multicast traffic, finding an optimal multicast light-tree is known to be NP-hard and is usually solved by first finding a link tree then finding a light tree on the link tree. Finding a link tree is also NP-hard and has been extensively studied. Thus, we focus on the second problem which is to set up a light tree on a given link tree with minimum number of conversions. We propose a new and more practical multicast conversion model, where the output of the wavelength converter can be split. As can be seen, the new model can save the usage of converters considerably. We first show that this problem is NP-hard and then give efficient heuristics to solve it approximately.

In this invited talk, we will review our recent development of an all-optical wavelength converter which satisfies the requirements for applications in practical all-optical networks. While providing a wideband conversion for almost all the C-band, excellent performance with dual-polarization quadrature phase shift keying (DP-QPSK) signals show a true modulation format independence with phase preserving and polarization insensitive operations. The converter features a counter-dithering pump scheme for cascaded dual-stage degenerate four wave mixing (FWM) processes to suppress the stimulated Brillouin scattering (SBS) in highly nonlinear fiber, and thus significantly improve the conversion efficiency, making it a low-loss and low-noise conversion. As a result, the total noise figure of the wavelength converter is reduced to 6.2 dB which is comparable to an EDFA. The cascaded operation of the wavelength converter is also investigated in a wavelength translating loop, showing negligible impacts of the phase noise transferred from pump signals on the idlers, or residual phase noise induced by the counter-dithering scheme. The obtained high cascadability as that of an EDFA indicates the true practicality of the developed wavelength converter for real system use.

It is true that in all-optical networks, network performance can be improved by wavelength conversion. However, the switching node with wavelength conversion capability is still costly, and the number of such nodes should be limited in the network. In this paper, a performance optimization problem is treated in all-optical networks. We propose a heuristic algorithm to minimize an overall blocking probability by properly allocating a limited number of nodes with wavelength conversion capability. The routing strategy is also considered suitable to the case where the number of wavelength convertible nodes are limited. We validate the minimization level of our heuristic algorithm through numerical examples, and show that our algorithm can properly allocate nodes with conversion for performance optimization.

A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion

Dynamic wavelength assignment in a WDM all-optical network with sparse wavelength conversion is discussed in this paper. The performance of unidirectional and bidirectional ring networks in terms of blocking probability, conversion gain and fairness are evaluated under various types of offered traffic patterns. Smooth and peaked patterns have been considered in addition to the classical Poisson traffic type. It is shown how the use of wavelength converters affects the blocking performance of connections and, more importantly in terms of network fairness, its dependence on the source-destination distance.

This paper examines wavelength translation in all-optical wavelength-routed networks. Previous studies have shown that wavelength translation can improve the blocking performance of these networks. However, all the previous work has assumed that wavelength translators can translate from any input wavelength to any output wavelength. In contrast, all-optical wavelength translators demonstrated in the laboratory to date are, in general, only capable of limited translation. We assess, for the first time, the network performance improvements offered by realistic all-optical wavelength translators with a limited translation range. In particular, we consider all-optical wavelength translators based on four-wave mixing in semiconductor optical amplifiers. Using a simple model for their function, we consider the blocking performance of two-hop and multiple-hop paths, and unidirectional ring and mesh-torus networks. In all the cases we consider, significant improvement in the blocking performance of the network is obtained when limited-range wavelength translators with as little as one quarter of the full range an introduced. We also find that almost all of the network performance improvement observed by an ideal wavelength translator can be gained from a translator with only half of the full translation range.