Jason Iness

Scheduling variable-length messages in a single-hop multichannel local lightwave network

The design of a medium access control scheme for a single-hop, wavelength-division-multiplexing-(WDM) multichannel local lightwave network poses two major difficulties: relatively large transmitter/receiver tuning overhead and large ratio of propagation delay to packet transmission time. Most schemes proposed so far have ignored the tuning overhead, and they can only schedule fixed-length packet transmissions. To overcome these two difficulties, the authors propose several scheduling algorithms which can reduce the negative impact of tuning overhead and schedule variable-length messages. A separate channel (control channel) is employed for transmission of control packets, and a distributed scheduling algorithm is invoked at each node every time it receives a control packet. By allowing the length of messages to be variable, a long message can be scheduled with a single control packet transmission, instead of fragmenting it into many fixed-length packets, thereby significantly reducing the overhead of control packet transmissions and improving the overall system performance. Three novel scheduling algorithms are proposed, varying in the amount of global information and processing time they need. Two approximate analytical models are formulated to study the effect of tuning time and the effect of having a limited number of data channels. Extensive simulations are conducted. Average message delays are compared for all of the algorithms. >

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.

GEMNET: a generalized, shuffle-exchange-based, regular, scalable, modular, multihop, WDM lightwave network

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied. >

Optimizing amplifier placements in a multiwavelength optical LAN/MAN: the equally powered-wavelengths case

Wavelength division multiplexing (WDM) provides the ability to utilize the enormous bandwidth offered by optical networks, using todays electronics. WDM-based optical networks employing passive-star couplers have been proposed for deployment in local and metropolitan areas. Optical amplification is often required in such networks to compensate for the signal attenuation along the fiber links and the splitting and coupling losses in the network. However, an optical amplifier has constraints on the maximum gain and the maximum output power it can supply; thus optical amplifier placement becomes a challenging problem. A simplifying assumption for analytical tractability requires that all wavelengths, present at a particular point in a fiber, be at the same power level, viz, the equally powered-wavelengths case. However, previous studies did not minimize the total number of amplifiers while achieving power equalization. In this paper, we formulate the minimization of amplifiers with power equalization as a mixed integer linear program (MILP) that can be solved by a linear program solver. Illustrative examples on sample networks are presented, which demonstrate the characteristics and the advantages of our optimal amplifier placement algorithm.

Variable-length message scheduling algorithms for a WDM-based local lightwave network

Two major difficulties in designing a single-hop multichannel local lightwave network are: relatively large transmitter/receiver tuning overhead and large ratio of propagation delay to packet transmission time. The authors propose several scheduling algorithms which can reduce the negative impact of tuning overhead and schedule variable-length messages. Thus, a long message can be scheduled with a single control packet transmission, instead of being segmented into many fixed-length packets, thereby significantly increasing the systems efficiency. Three novel scheduling algorithms are proposed, varying in the amount of global information and processing time. Two approximate analytical models are formulated to study the effect of tuning time and the effect of having a limited number of data channels. The systems performance is found to improve (1) if a simple mechanism is employed to avoid unnecessary transceiver tuning and/or (2) if a predictive transmitter tuning strategy is adopted.<<ETX>>

New modular architectures for regular multihop lightwave networks

By using WDM channels and tunable transceivers, arbitrary virtual topologies can be mapped onto physical-topology optical networks. Regular connectivity patterns with small nodal degree, simple routing, and small network diameter are attractive candidates for logical topologies. ShuffleNet1 and de Bruijn graph2,3 are two such networks, but they are not easily scalable. For example, ShuffleNet and de Bruijn graph must have KP“and P’ nodes, respectively, where D,P= 2, 3,…, and K = 1, 2, 3, .… We propose two new network architectures, GEMNET and MRNET, that are modular and scalable. The modularity of these networks equals the nodal degree P, and generally they both have properties comparable to or better than de Bruijn graph, ShuffleNet, and Manhattan Street Network.4 GEMNET is based on a generalized shuffle-exchange connectivity pattern,4 and MRNET is based on a modification of RegularNet5 for simplified routing. Formal descriptions of GEMNET and MRNET and the comparative performance of various regular multihop network architectures are given below. However, derivations are omitted to conserve space.

New Optical Amplifier Placement Schemes for Broadcast Networks

WDM optical broadcast networks (based on the passive-star coupler) may encounter large splitting and attenuation losses that need to be compensated for using optical amplifiers, such as EDFAs. However, optical amplifiers are costly, so their total count in the network should be minimized. This study will examine three different such amplifier-placement schemes. The first approach utilize fewer amplifiers than previous schemes that do not add special hardware to avoid the near-far effect. The second study considers a bidirectionai-link network and it can use fewer amplifiers than a comparable unidirectional-link network. The third study minimizes the number of amplifiers when the amplifiers are equipped with special hardware to avoid the near-far effect, i.e., amplifiers are equipped with attenuators/filters to equalize amplifier input power on different wavelengths.

Optical interconnects for multiprocessor architectures using wavelength-division multiplexing

Multiprocessor architectures based on optical interconnects employing wavelength division multiplexing (WDM) are considered. WDM is a technique used to divide the tremendous bandwidth of a single strand of fiber into many non-interfering wavelengths. System components (processing, memory, and/or I/O elements) can use these wavelengths as communication channels. The authors present the background needed to understand WDM architecture, outline several categories of single-hop communication protocols, and show how a multihop WDM-based multiprocessor can reconfigure itself to any virtual topology.<<ETX>>