To support bursty traffic on the Internet (and especially WWW) efficiently, optical burst switching (OBS) is proposed as a way to streamline both protocol and hardware in building the future generation Optical Internet. By leveraging the attractive properties of optical communications and at the same time, taking into account its limitations, OBS combines the best of optical circuitswitching and packet/cell switching. In this paper, the general concept of OBS protocols and in particular, those based on Just-Enough-Time (JET), is described, along with the applicability of OBS protocols to IP over WDM. Specific issues such as the use of fiber delay-lines (FDL) for accommodating processing delay and/or resolving conflicts are also discussed. In addition, the performance of JET-based OBS protocols which use an offset time along with delayed reservation to achieve efficient utilization of both bandwidth and FDLs as well as to support priority-based routing is evaluated.

This paper considers the problem of routing connections in a reconfigurable optical network using wavelength division multiplexing, where each connection between a pair of nodes in the network is assigned a path through the network and a wavelength on that path, such that connections whose paths share a common link in the network are assigned different wavelengths. We derive an upper bound on the carried traffic of connections (or equivalently, a lower bound on the blocking probability) for any routing and wavelength assignment (RWA) algorithm in such a network. The bound scales with the number of wavelengths and is achieved asymptotically (when a large number of wavelengths is available) by a fixed RWA algorithm. Although computationally intensive, our bound can be used as a metric against which the performance of different RWA algorithms can be compared for networks of moderate size. We illustrate this by comparing the performance of a simple shortest-path RWA (SP-RWA) algorithm via...

This study focuses on the routing and Wavelength-Assignment (RWA) problem in wavelength-routed optical WDM networks. Most of the attention is devoted to such networks operating under the wavelength-continuity constraint, in which lightpaths are set up for connection requests between node pairs, and a single lightpath must occupy the same wavelength on all of the links that it spans. In setting up a lightpath, a route must be selected and a wavelength must be assigned to the lightpath. If no wavelength is available for this lightpath on the selected route, then the connection request is blocked. We examine the RWA problem and review various routing approaches and wavelengthassignment approaches proposed in the literature. We also briefly consider the characteristics of wavelength-converted networks (which do not have the wavelength-continuity constraint), and we examine the associated research problems and challenges. Finally, we propose a new wavelengthassignment scheme, called Distributed Relative Capacity Loss (DRCL), which works well in distributed-controlled networks, and we demonstrate the performance of DRCL through simulation. 1

This paper studies the problem of designing a logical topology over a wavelengthrouted all-optical network physical topology. The physical topology consists of the nodes and fiber links in the network. On an all-optical network physical topology, we can set up lightpaths between pairs of nodes, where a lightpath represents a direct optical connection without any intermediate electronics. The set of lightpaths along with the nodes constitutes the logical topology. For a given network physical topology and traffic pattern (relative traffic distribution among the source-destination pairs), our objective is to design the logical topology and the routing algorithm on that topology so as to minimize the network congestion while constraining the average delay seen by a sourcedestination pair and the amount of processing required at the nodes (degree of the logical topology). We will see that ignoring the delay constraints can result in fairly convoluted logical topologies with very...

We study a class of all-optical networks using wavelength division multiplexing and wavelength routing in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: Fixed Routing and Least Loaded Routing. 1 Introduction We study a class of all-optical networks using wavelength division multiplexing and wavelength routing [4] in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. While we will refer to this type of network as the 'wavelength routing' model we should point out that a routing scheme for the connections through the the network is not implied, ...

We consider large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed (WDM) channels, called lightpaths, between node pairs. We propose a practical approach to solve routing and wavelength assignment (RWA) of lightpaths in such networks. A large RWA problem is partitioned into several smaller subproblems, each of which may be solved independently and efficiently using wellknown approximation techniques. A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths. Wavelength assignments for lightpaths are performed based on graph-coloring techniques. Representative numerical examples indicate the accuracy of our algorithms. 1 Introduction Wavelength division multiplexing (WDM) can divide the tremendous bandwidth of a fiber (potentially a few tens of terabits per second) into many non-overlapping wavelengths (WDM channels). Each channel can be oper...

In the past few years, there has been growing interest in wide area "All Optical Networks" with wavelength division multiplexing (WDM), using wavelength routing. Due to the huge bandwidth inherent in optical fiber, and the use of WDM to match user and network bandwidths, the wavelength routing architecture is an attractive candidate for future backbone transport networks. A virtual topology over a WDM WAN consists of clear channels between nodes called lightpaths, with traffic carried from source to destination without electronic switching "as far as possible", but some electronic switching may be performed. Virtual topology design aims at combining the best of optical switching and electronic routing abilities. Designing a virtual topology on a physical network consists of deciding the lightpaths to be set up in terms of their source and destination nodes and wavelength assignment. In this survey we first describe the context and motivations of the virtual topology design ...

In this paper, we consider routing and wavelength assignment in wavelength-routed alloptical networks with circuit-switching. The conventional approaches to address this issue consider the two aspects of the problem sequentially by first finding a route from a predetermined set of candidate paths and then searching for an appropriate wavelength assignment. We adopt a more general approach in which we consider all paths between a source-destination pair and incorporate network state information into the routing decision. This approach performs routing and wavelength assignment jointly and adaptively, and outperforms fixed routing techniques. We present adaptive routing and wavelength assignment algorithms and evaluate their blocking performance. We obtain an algorithm to compute approximate blocking probabilities for networks employing fixed and alternate routing techniques. That algorithm can also accommodate networks with multiple fibers per link. The blocking performance of the propo...

Wavelength division multiplexing technology is emerging as the transmission and switching mechanism for future optical mesh networks. In these networks, it is desired that a wavelength can be routed without electrical conversions. Two technologies are possible for this purpose: Wavelength Selective Cross-Connects (WSXC), and Wavelength Interchanging Cross-Connects (WIXC) which involve wavelength conversion. It is believed that wavelength converters may improve the blocking performance, but there is a mix of results in the literature on the amount of this performance enhancement. In this paper, we use two metrics to quantify the wavelength conversion gain: the reduction in blocking probability and the increase in maximum utilization, compared to a network without converters. We study effects of wavelength routing and selection algorithms on these measures for mesh networks. We use the Overflow Model to analyze the blocking probability for wavelength selective mesh networks using the Fir...

This paper proposes optical wavelength division multiplexed (WDM) networks with limited wavelength conversion that can efficiently support lightpaths (connections) between nodes. Each lightpath follows a route in the network and must be assigned a channel along each link in its route. The load max of a set of lightpath requests is the maximum over all links of the number of lightpaths that use the link. At least max wavelengths will be needed to assign channels to the lightpaths. If the network has full wavelength conversion capabilities then max wavelengths are sufficient to perform the channel assignment. We propose ring networks with fixed wavelength conversion capability within the nodes that can support all lightpath request sets with load max at most W \Gamma 1, where W is the number of wavelengths in each link. We also propose ring networks with selective pairwise wavelength conversion capability within the nodes that can support all lightpath request sets with l...