Multinode broadcast in hypercubes and rings with randomlydistributed length of packets

Multinode broadcast (MNB) in a hypercube and in a ring network of processors is considered. It is assumed that the lengths of the packets that are broadcast are not fixed, but are distributed according to some probabilistic rule, and the optimal times required to execute the MNB are compared for variable and for fixed packet lengths. For large hypercubes, it is shown, under very general probabilistic assumptions on the packet lengths, that the MNB is completed in essentially the same time as when the packet lengths are fixed. In particular, the MNB is completed by time (1+δ)T_s with probability at least 1-ϵ, for any positive ϵ and δ, where T _s is the optimal time required to execute the MNB when the packet lengths are fixed at their mean, provided that the size of the hypercube is large enough. In the case of the ring, it is proved that the average time required to execute a MNB when the packet lengths are exponentially distributed exceeds by a factor of ln n the corresponding time for the case there the packet lengths are fixed at their mean, where n is the number of nodes of the ring     

Multi‐cost routing for energy and capacity constrained wireless mesh networks

We propose a class of novel energy‐efficient multi‐cost routing algorithms for wireless mesh networks, and evaluate their performance. In multi‐cost routing, a vector of cost parameters is assigned to each network link, from which the cost vectors of candidate paths are calculated using appropriate operators. In the end these parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. We evaluate the performance of the proposed energy‐aware multi‐cost routing algorithms under two models. In the network evacuation model, the network starts with a number of packets that have to be transmitted and an amount of energy per node, and the objective is to serve the packets in the smallest number of steps, or serve as many packets as possible before the energy is depleted. In the dynamic one‐to‐one communication model, new data packets are generated continuously and nodes are capable of recharging their energy periodically, over an infinite time horizon, and we are interested in the maximum achievable steady‐state throughput, the packet delay, and the energy consumption. Our results show that energy‐aware multi‐cost routing increases the lifetime of the network and achieves better overall network performance than other approaches. Copyright © 2011 John Wiley & Sons, Ltd.     

Fair Scheduling Algorithms in Grids

In this paper, we propose a new algorithm for fair scheduling, and we compare it to other scheduling schemes such as the earliest deadline first (EDF) and the first come first served (FCFS) schemes. Our algorithm uses a max-min fair sharing approach for providing fair access to users. When there is no shortage of resources, the algorithm assigns to each task enough computational power for it to finish within its deadline. When there is congestion, the main idea is to fairly reduce the CPU rates assigned to the tasks so that the share of resources that each user gets is proportional to the users weight. The weight of a user may be defined as the users contribution to the infrastructure or the price he is willing to pay for services or any other socioeconomic consideration. In our algorithms, all tasks whose requirements are lower than their fair share CPU rate are served at their demanded CPU rates. However, the CPU rates of tasks whose requirements are larger than their fair share CPU rate are reduced to fit the total available computational capacity in a fair manner. Three different versions of fair scheduling are adopted in this paper: the simple fair task order (SFTO), which schedules the tasks according to their respective fair completion times, the adjusted fair task order (AFTO), which refines the SFTO policy by ordering the tasks using the adjusted fair completion time, and the max-min fair share (MMFS) scheduling policy, which simultaneously addresses the problem of finding a fair task order and assigning a processor to each task based on a max-min fair sharing policy. Experimental results and comparisons with traditional scheduling schemes such as the EDF and the FCFS are presented using three different error criteria. Validation of the simulations using real experiments of tasks generated from 3D image- rendering processes is also provided. The three proposed scheduling schemes can be integrated into existing grid computing architectures.     

An analysis of oblivious and adaptive routing in optical networkswith wavelength translation

We present an analysis for both oblivious and adaptive routing in regular, all-optical networks with wavelength translation. Our approach is simple, computationally inexpensive, accurate for both low and high network loads, and the first to analyze adaptive routing with wavelength translation in wavelength division multiplexed (WDM) networks while also providing a simpler formulation of oblivious routing with wavelength translation. Unlike some previous analyses which use the link independence blocking assumption and the call dropping (loss) model (where blocked calls are cleared), we account for the dependence between the acquisition of wavelengths on successive links of a session's path and use a lossless model (where blocked calls are retried at a later time). We show that the throughput per wavelength increases superlinearly (as expected) as we increase the number of wavelengths per link, due both to additional capacity and more efficient use of this capacity; however, the extent of this superlinear increase in throughput saturates rather quickly to a linear increase. We also examine the effect that adaptive routing can have on performance. The analytical methodology that we develop can be applied to any vertex and edge symmetric topology, and with modifications, to any vertex symmetric (but not necessarily edge symmetric) topology. We find that, for the topologies we examine, providing at most one alternate link at every hop gives a per wavelength throughput that is close to that achieved by oblivious routing with twice the number of wavelengths per link. This suggests some interesting possibilities for network provisioning in an all-optical network. We verify the accuracy of our analysis for both oblivious and adaptive routing via simulations for the torus and hypercube networks     

Statistical Simulation Modeling of 3-D HAP-MIMO Channels

High altitude platforms (HAPs) have been designated as an alternative wireless infrastructure for facilitating next generation high-speed mobile communications services. This paper deals with the design and performance evaluation of a three-dimensional (3-D) sum-of-sinusoids statistical simulation model for HAP multiple-input?Cmultiple-output Ricean fading channels. The performance of the simulation model is investigated with respect to the temporal and spatial correlation functions. The results indicate that the simulation model accurately and efficiently approximates the statistical properties of a recently proposed non-realizable reference model.     

The “packing” and the “scheduling packet”switch architectures for almost all-optical lossless networks

This paper proposes two almost all-optical packet switch architectures, called the “packing switch” and the “scheduling switch” architecture, which when combined with appropriate wait-for-reservation or tell-and-go connection and how control protocols provide lossless communication for traffic that satisfies certain smoothness properties. Both switch architectures preserve the order of packets that use a given input-output pair, and are consistent with virtual circuit switching, The scheduling switch requires 2klogT+k² two-state elementary switches (or 2klogT+2klogk elementary switches, if a different version is used) where k is the number of inputs and T is a parameter that measures the allowed burstiness of the traffic. The packing switch requires very little processing of the packet header, and uses k²logT+klogk two-state switches. We also examine the suitability of the proposed architectures for the design of circuit switched networks. We find that the scheduling switch combines low hardware cost with little processing requirements at the nodes, and is an attractive architecture for both packet-switched and circuit-switched high-speed networks     

Wideband HAP-MIMO Channels: A 3-D Modeling and Simulation Approach

High-altitude platforms (HAPs) are considered as an alternative technology to provide future generation broadband wireless communications services. This paper proposes a three-dimensional (3-D) geometry-based reference model for wideband HAP multiple-input–multiple-output (MIMO) channels. The statistical properties of the channel are analytically studied in terms of the elevation angle of the platform, the antenna arrays configuration, and the angular, the Doppler and the delay spread. Specifically, the space-time-frequency correlation function (STFCF), the space-Doppler power spectrum, and the power space-delay spectrum are derived for a 3-D non-isotropic scattering environment. Finally, a sum-of-sinusoids statistical simulation model for wideband HAP-MIMO channels is proposed. The results show that the simulation model accurately and efficiently reproduces the STFCF of the reference model. The proposed models provide a convenient framework for the characterization, analysis, test, and design of wideband HAP-MIMO communications systems with line-of-sight and non-line-of-sight links.     

Pathogenesis and characterization of hyperglucagonemia in the uremic rat

The pathogenesis of hyperglucagonemia and of the alterations in the pattern of circulating immunoreactive glucagon (IRG) associated with renal insufficiency was studied in rats in which a comparable degree of uremia was induced by three different methods, i.e., bilateral nephrectomy, bilateral ureteral ligation, and urine autoinfusion. Nephrectomized and ureteral-ligated rats were markedly hyperglucagonemic (575 +/- 95 pg/ml and 492 +/- 54 pg/ml, respectively), while IRG levels of urine autoinfused animals (208 +/- 35 pg/ml) were similar to those of control rats (180 +/- 26 pg/ml), indicating that uremia per se does not account for the hyperglucagonemia observed in renal failure. Similarly, plasma IRG composition in this group of animals was indistinguishable from that of controls, in which 88.2 +/- 5.9% of total IRG consisted of the 3,500-mol wt fraction. The same component was almost entirely responsible (82.6 +/- 4.1%) for the hyperglucagonemia observed in ligated rats, while it accounted for only 57.6 +/- 5.0% of the circulating IRG in nephrectomized animals. In the latter group, 36.8 +/- 6.6% of total IRG had a mol wt of approximately 9,000, consistent with a glucagon precursor. This peak was present in samples obtained as early as 2 h after renal ablation and its concentration continued to increase with time reaching maximal levels at 24 h. These results confirm that the kidney is a major site of glucagon metabolism and provide evidence that the renal handling of the various circulating IRG components may involve different mechanisms. Thus, the metabolism of the 3,500-mol wt fraction is dependent upon glomerular filtration, while the uptake of the 9,000-mol wt material can proceed in its absence, as long as renal tissue remains adequately perfused. This finding suggests that the 9,000-mol wt component may be handled by peritubular uptake.     

A Bandwidth Monitoring Mechanism Enhancing SNMP to Record Timed Resource Reservations

The efficient use of resources and the lossless transfer of data bursts in future optical networks requires the accurate knowledge of the available bandwidth for each network link. Such information is important in monitoring congestions and can be used by appropriate load balancing and congestion avoidance mechanisms. In this paper we propose a mechanism for monitoring and subsequently managing bandwidth resources, using the Simple Network Management Protocol (SNMP). In the proposed mechanism, link bandwidth availability is not a scalar parameter, but a function of time that records the future utilization of the link. For every output port, each agent-node maintains a simple data structure in the form of a table that records the utilization profile of that outgoing link. With the addition of new objects in the Management Information Base (MIB) of each agent-node and proper synchronization, SNMP can be used to update and retrieve the reservations made on the links in order to obtain an instant picture of the network traffic situation.