The paper examines the delay performance of multicast switches with multiple input queues per input buffer. Under the assumptions of a Poisson uniform traffic pattern, random packet assigning policy, ...and random packet scheduling policy, we derive the packet delay and service time under different fanouts. To verify this analysis, extensive simulations are conducted with various fanouts, numbers of queues, and packet arrival rates. It is shown that the theoretical results agree well with the simulation results. The analysis proves that it is possible to predict how much the packet delay could be decreased through introducing more input queues per input buffer.
We present a complete analysis of delays for a tandem network of queues with deterministic service and multiple , interfering sources. The model is of a packet-based data collection system consisting ...of some finite, but arbitrary, number of stations connected in tandem by a unidirectional, asynchronous transmission network. Packets, or, more generally, tasks enter the system at every station, are handed from station to station in store-and-forward fashion, and exit at the downstream end; there are no intermediate departures. The stations are provided with infinite storage, and the lines between them operate concurrently and asynchronously. Intermediate sources are Poisson; the source at the head of the network can be somewhat more general than Poisson. Tasks from each source wait at each station downstream of their point of origin. We calculate the joint steady-state moment-generating functions for these waiting times, provided that the line capacities do not increase in the direction of flow; the solution contains as a special case the steady-state moment-generating function for end-to-end delay for each source.
The viability of Xanthobacter autotrophicus strain N34 and its oxygen-resistant segregant, strain Y38, was investigated after freezing and freeze-drying. The maintenance of oxygen-resistance of ...strain Y38 was also estimated by the results of plate cultivation method and liquid cultivation method under high oxygen tension. The viability of both strains immediately after freeze-drying was about 50%, while that after freezing was over 95%. Moreover, the viability of freeze-dried cells of both strains after storage for 24 months decreased markedly, showing that X. autotrophicus is highly sensitive to freeze-drying as already reported. From the result of plate cultivation, oxygen-resistance of strain Y38 seemed to be completely maintained after freezing or freeze-drying. On the other hand, from the result of growth delay analysis in liquid cultivation, only 24% of cells maintained oxygen-resistance immediately after freeze-drying, while almost 100% was maintained after freezing. Moreover, after storage for 24 months oxygen-resistance of frozen or freeze-dried materials was markedly decreased. The difference between the results of two cultivations indicated that many nonlethally injured cells existed among apparent oxygen-resistant cells grown on the plate under high oxygen tension.
We provide a comprehensive delay and queueing analysis for two baseline medium access control protocols for multi-user cognitive radio networks with homogeneous users and channels and investigate the ...impact of different network parameters on the system performance. In addition to an accurate Markov chain, which follows the queue status of all users, several lower complexity queueing theory approximations are provided. Accuracy and performance of the proposed analytical approximations are verified with extensive simulations. It is observed that using an Aloha-type access to the control channel, a buffering MAC protocol, where in case of interruption the CR user waits for the primary user to vacate the channel before resuming the transmission, outperforms a switching MAC protocol, where the CR user vacates the channel in case of appearance of primary users and then compete again to gain access to a new channel. The reason is that the delay bottleneck for both protocols is the time required to successfully access the control channel, which occurs more frequently for the switching MAC protocol. It is thus shown that a clustering approach, where users are divided into clusters with a separate control channel per cluster, can significantly improve the performance by reducing the competitions over control channel.
This paper studies resource scheduling for wireless small cloud assuming that the execution of an application is modeled as a workflow graph. A scheduling method is proposed which consists of two ...parts. For the task-to-computing-unit assignment part which operates on the long-term time-scale, the solution is to partition the workflow into task groups which have loose data transfer constraint and each task group is assigned to the computing unit which can finish executing the task group at the earliest time. For the computing and wireless communication resource scheduling part which operates on the short-term time-scale, we simply use the round-robin principle. A part by part delay component estimation method is presented based on which the average delay performance can be analyzed. Simulation results validate the theoretical analysis and show that the proposed method outperforms existing methods. The impact of different parameter settings on the system performance is also investigated.
ARIES is a workstation-based, schematic-driven software system for circuit design. It is divided into four major subsystems: SIZING, which generates transistor equivalents for logic gates (NMOS & ...CMOS technologies) and calculates their sizes (Widths & Lengths); PATHDELAY, which calculates path delays for circuits designed using standard cells; GRAPHICS, a 2-D plotting package that displays results from simulation programs such as SPICE, SUPREM, GEMINI and SUXES; and CANDETOSPICE, which generates, downloads remotely and executes circuit simulation input text files on a VAX 11/780. SIZING, PATHDELAY and CANDE2SPICE use CANDE, a schematic entry graphics editor and database as their front-end. ARIES runs interactively in a multiple overlapping bitmap window (concurrent processing) environment and is completely menu driven. All workstations and VAX 11/780's are connected together via several 10 MB Ethernet LANs.
The exact analytical model of DQDB is known to have state space explosion problem which makes its analysis intractable. The approximate single-node analytical model, introduced in a paper by ...Bisdikian and extended in a paper by Jing and Paterakis, has been proven to be a tractable model capable of providing valuable insight into the DQDB network behavior. In this paper, we show how to further extend the single-node model to approximately evaluate the average message delay of individual nodes for an entire network. We discuss the difficulties involved in applying the single-node model network-wide and approaches to circumvent these difficulties. We present some representative approximate mean message delay results. Finally, with the help of simulations, we study the effect of an analytical approximation—
Bernoulli Slot Occupancy—on the mean message delay over DQDB networks.
With the rapid proliferation of broadband wireless services, it is of paramount importance to understand how fast data can be sent through a wireless local area network (WLAN). Thanks to a large body ...of research following the seminal work of Bianchi, WLAN throughput under saturated traffic condition has been well understood. By contrast, prior investigations on throughput performance under unsaturated traffic condition was largely based on phenomenological observations, which lead to a common misconception that WLAN can support a traffic load as high as saturation throughput, if not higher, under nonsaturation condition. In this paper, we show through rigorous analysis that this misconception may result in unacceptable quality of service: mean packet delay and delay jitter may approach infinity even when the traffic load is far below the saturation throughput. Hence, saturation throughput is not a sound measure of WLAN capacity under nonsaturation condition. To bridge the gap, we define safe-bounded-mean-delay (SBMD) throughput and safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network capacity users can enjoy when they require finite mean delay and delay jitter, respectively. Our earlier work proved that in a WLAN with multi-packet reception (MPR) capability, saturation throughput scales superlinearly with the MPR capability of the network. This paper extends the investigation to the nonsaturation case and shows that superlinear scaling also holds for SBMD and SBDJ throughputs. Our results here complete the demonstration of MPR as a powerful capacity-enhancement technique for WLAN under both saturation and nonsaturation conditions.
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