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doi: 10.1177/0037549707080605pmid: N/A
The number of households and businesses using hybrid fiber coaxial cable networks for Internet access is rapidly approaching 40 million in the United States. The cable industry has standardized on a single medium access control (MAC) and physical layer standard, the Data Over Cable Service Interface Specification (DOCSIS). The MAC layer of the emerging IEEE 802.16 broadband wireless access standard is also based upon DOCSIS. Thus, the performance of DOCSIS is now and will remain a critical element in the overall performance of shared medium broadband access networks. Despite this fact, public domain tools that may be used to assess and improve the performance of DOCSIS have been slow to emerge. To address this problem, we have implemented a simulation model of the DOCSIS MAC layer for the `ns' network simulation tool. Due to the complexity of DOCSIS and because the specifications are purposely incomplete, developing an accurate simulation is quite challenging. In this paper we present analytic and live network evidence that the simulation accurately reflects the behavior of a DOCSIS network under a limited set of workloads.
Viswanath, Kumar; Obraczka, Katia; Kottas, Athanasios; Sansó, Bruno
doi: 10.1177/0037549707080610pmid: N/A
Statistical Equivalent Models, or SEMs, have recently been proposed as a general approach to study computer simulators. By fitting a statistical model to the simulator's output, SEMs provide an efficient way to quickly explore the simulator's result. In this paper, we develop a SEM for random waypoint mobility, one of the most widely used mobility models employed by network simulators in the evaluation of communication protocols for wireless multi-hop ad hoc networks (MANETs). We chose the random waypoint mobility model as a case study of SEMs due to recent results pointing out some serious drawbacks of the model (e.g., [1]). In particular, these studies show that, under the random waypoint mobility regime, average node speed tends to zero in steady state. They also show that average node speed varies considerably from the expected average value for the time scales under consideration in most simulation analysis. In order to investigate further the behavior of the random waypoint model, we developed a SEM that captured speed decay over time under random waypoint mobility using maximum speed and terrain size as input parameters. A Bayesian approach to model fitting was employed to capture the uncertainty due to unknown parameters of the statistical model. The SEM is given by the posterior predictive distributions of the average node speed as a function of time. A direct result from our model is that, by characterizing average node speed as a function of time, our approach provides an accurate estimate of the “warm-up” period required by simulations using the random waypoint mobility model. Simulation data from the “warmup” period can then be discarded to obtain accurate protocol performance results. Given that random waypoint mobility is still, by far, the most widely used mobility model in the evaluation of MANETs, the contribution of this work is potentially significant as it allows network protocol designers to continue to use the original random waypoint mobility model and yet obtain accurate results characterizing MANET protocol performance.
Boudriga, Noureddine; Lazzez, Amor; Obaidat, Mohammad S.
doi: 10.1177/0037549707080603pmid: N/A
Among the promising solutions for next generation Internet backbone, one can consider optical burst switching (OBS) technology. This technology does not, however, provide suitable quality-of-service (QoS) support. Several schemes have been proposed to provide QoS differentiation in OBS networks. The majority of these schemes are based on a relative QoS model in which the performance of a given traffic class is defined in comparison with other classes. A set of mechanisms have been proposed to provide an absolute traffic loss guarantee, but no mechanism has been proposed to handle absolute transmission delay in OBS networks. The aim of this paper is to propose a solution to provide an absolute transmission delay guarantee over an OBS network and thus support emerging multimedia applications with delay and bandwidth constraints based on a network architecture that is suitable for OBS switching and QoS provisioning. We also develop an analytic model based on a queuing system of the proposed solution. Finally, simulation experiments are conducted to validate the proposed scheme and study its features.
doi: 10.1177/0037549707080608pmid: N/A
Many core-stateless mechanisms have been proposed to resolve the scalability problem in the core routers. However, they place considerable reliance on the edge routers or anterior core routers to mark correct flow information in corresponding packets. As a result, the condition of incorrect flow information may severely degrade the fairness among different flows. To achieve the robust fairness, an approximately core-stateless fair sharing mechanism, self-configured fair queuing (SCFQ) is proposed in this paper. This mechanism is mainly composed of two rate estimators; one estimator is used to estimate the arrival rate of the malicious flows that can be adopted to emend the incorrect flow information of the arrival packets. The other one is used to estimate the fair share rate. Computer Simulation is applied to compare the fairness of the SCFQ, core-stateless fair queuing (CSFQ), linear fair sharing estimation (LFSE), deficit round robin (DRR), and first in first out (FIFO). From the simulation results, the SCFQ is capable of supporting much better fairness than that of other compared mechanisms under a variety of traffic conditions. Also, the overhead of the SCFQ is low, so it is very suitable to be deployed in high-speed core routers.
Stafford, Shad; Jun Li, ; Ehrenkranz, Toby
doi: 10.1177/0037549707080753pmid: N/A
Once a host is infected by an Internet worm, prompt action must be taken before that host does more harm to its local network and the rest of the Internet. It is therefore critical to quickly detect that a worm has infected a host. In this paper, we enhance our SWORD system to allow for the detection of infected hosts and evaluate its performance. This enhanced version of SWORD inherits the advantages of the original SWORD: it does not rely on inspecting traffic payloads to search for worm byte patterns or setting up a honeypot to lure worm traffic. Furthermore, while acting as a host-level detection system, it runs at a network's gateway and stays transparent to individual hosts. We show that our enhanced SWORD system is able to quickly and accurately detect if a host is infected by a zero-day worm. Furthermore, the detection is shown to be effective against worms of different types and speeds, including polymorphic worms
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