Multicast routing with end-to-end delay and delay variationconstraints

We study the problem or constructing multicast trees to meet the quality of service requirements of real-time interactive applications operating in high-speed packet-switched environments. In particular, we assume that multicast communication depends on: (1) bounded delay along the paths from the source to each destination and (2) bounded variation among the delays along these paths. We first establish that the problem of determining such a constrained tree is NP-complete. We then present a heuristic that demonstrates good average case behavior in terms of the maximum interdestination delay variation. The heuristic achieves its best performance under conditions typical of multicast scenarios in high speed networks. We also show that it is possible to dynamically reorganize the initial tree in response to changes in the destination set, in a way that is minimally disruptive to the multicast session     

JumpStart: a just-in-time signaling architecture for WDMburst-switched networks

We present an architecture for a core dWDM network which utilizes the concept of optical burst switching coupled with a just-in-time signaling scheme. It is a reservation-based architecture whose distinguishing characteristics are its relative simplicity, its amenability to hardware implementation, and the ability to support multicast natively. Another important feature is data transparency-the network infrastructure is independent of the format of the data being transmitted on individual wavelengths. We present the signaling protocol designed for this architecture, as well as an unified signaling message structure to be used in conjunction with the protocol. We also present the future directions of this research     

Reconfiguration and Dynamic Load Balancing in Broadcast WDM Networks*

In optical WDM networks, an assignment of transceivers to channels implies an allocation of the bandwidth to the various network nodes. Intuition suggests, and our recent study has confirmed, that if the traffic load is not well balanced across the available channels, the result is poor network performance. Hence, the time-varying conditions expected in this type of environment call for mechanisms that periodically adjust the bandwidth allocation to ensure that each channel carries an almost equal share of the corresponding offered load. In this paper we study the problem of dynamic load balancing in broadcast WDM networks by retuning a subset of transceivers in response to changes in the overall traffic pattern. Assuming an existing wavelength assignment and some information regarding the new traffic demands, we present two approaches to obtaining a new wavelength assignment such that (a) the new traffic load is balanced across the channels, and (b) the number of transceivers that need to be retuned is minimized. The latter objective is motivated by the fact that tunable transceivers take a non-negligible amount of time to switch between wavelengths during which parts of the network are unavailable for normal operation. Furthermore, this variation in traffic is expected to take place over larger time scales (i.e., retuning will be a relatively infrequent event), making slowly tunable devices a cost effective solution. Our main contribution is a new approximation algorithm for the load balancing problem that provides for tradeoff selection, using a single parameter, between two conflicting goals, namely, the degree of load balancing and the number of transceivers that need to be retuned. This algorithm leads to a scalable approach to reconfiguring the network since, in addition to providing guarantees in terms of load balancing, the expected number of retunings scales with the number of channels, not the number of nodes in the network.     

Traffic adaptive WDM networks: a study of reconfiguration issues

This paper studies the issues arising in the reconfiguration phase of broadcast optical networks. Although the ability to dynamically optimize the network under changing traffic conditions has been recognized as one of the key features of multi-wavelength optical networks, this is the first in-depth study of the tradeoffs involved in carrying out the reconfiguration process. We develop and compare reconfiguration policies to determine when to reconfigure the network, and we present an approach to carry out the network transition by describing a class of strategies that determine how to retune the optical transceivers. We identify the degree of load balancing and the number of retunings as two important, albeit conflicting, objectives in the design of reconfiguration policies, naturally leading to a formulation of the problem as a Markovian decision process. Consequently, we develop a systematic and flexible framework in which to view and contrast reconfiguration policies. We show how an appropriate selection of reward and cost functions can be used to achieve the desired balance among various performance criteria of interest. We conduct a comprehensive evaluation of reconfiguration policies and retuning strategies and demonstrate the benefits of reconfiguration through both analytical and simulation results. The result of our work is a set of practical techniques for managing the network transition phase that can be directly applied to networks of large size. Although our work is in the context of broadcast networks, the results can be applied to any wavelength-division multiplexing network where it is necessary to multiplex traffic from a large user population into a number of wavelengths