Minimizing delay and packet loss in single-hop lightwave WDM networks using TDM schedules

Abstract

We consider packet-switched lightwave WDM networks with stations equipped with tunable transmitters and fixed receivers. Access to each of the available channels is controlled by a weighted TDM scheme, whereby the channels are not necessarily shared equally among the various sources. While previous work focused on the throughput characteristics of such schemes, in this paper we study the problem of designing TDM frames to minimize the mean packet delay, as well as the mean packet loss probability given a finite buffer capacity. The corresponding optimization problems are shown to be hard allocation problems, and heuristics to obtain near-optimal solutions are developed. For (potentially non-uniform) communication patterns common to parallel and distributed computations, oUI approach represents a significant improvement over I-TDMA*. In addition, the margin of improvement increases with the size of the network.

On the design of optimal TDM schedules for broadcast WDM networks with arbitrary transceiver tuning latencies

“…Proof (of Theorem 4.1). It is easy to see that OSTL is in the class NP, since a nondeterministic algorithm need only (a) guess the optimal set of start slots f ic g satisfying constraints (5), and (b) (6) and verify that the length of the schedule is less than or equal to M.…”

“…We can obtain a di erent lower bound by adopting a transmitter's point of view. Each transmitter i needs a number of slots equal to the number of packets it has to transmit plus the number of slots required to tune to each of C wavelengths 6 . We call this the tuning bound:…”

“…Accordingly, a padding equal to time units can be included within each slot to allow the transceivers su cient time to switch between wavelengths, with minimal e ects on the overall performance. This is re ected in the design of network architectures and protocols for such environments 5,6,7,8,9,10] which has been geared towards improving the delay and throughput characteristics of the network under various tra c assumptions, completely ignoring transceiver tuning times.…”

“…Constraints (34) and (35) are essentially the no-collision constraints (6); they ensure that transmissions by some node i on some channel c start after the end of transmissions by node i ? 1 on the same channel.…”

Adaptive bandwidth allocation schemes for lightwave LANs with asymmetric traffic

“…1 asymmetric traffic is offered to a WDM star network, the available bandwidth must be allocated to the sourcestations in such a way that each station takes a portion of the bandwidth proportional to its needs. When the traffic characteristics are k e d and a priori known [8], then the bandyidth allocation scheme can be based on these characteristics. Unfortunately, the traffic characteristics are often unknown and time-variable.…”