323 research outputs found
Wavelength converter sharing in asynchronous optical packet/burst switching: An exact blocking analysis for markovian arrivals
Cataloged from PDF version of article.In this paper, we study the blocking probabilities
in a wavelength division multiplexing-based asynchronous
bufferless optical packet/burst switch equipped with a bank of
tuneable wavelength converters dedicated to each output fiber
line. Wavelength converter sharing, also referred to as partial
wavelength conversion, corresponds to the case of a number
of converters shared amongst a larger number of wavelength
channels. In this study, we present a probabilistic framework for
exactly calculating the packet blocking probabilities for optical
packet/burst switching systems utilizing wavelength converter
sharing. In our model, packet arrivals at the optical switch are
first assumed to be Poisson and later generalized to the more
general Markovian arrival process to cope with very general
traffic patterns whereas packet lengths are assumed to be exponentially
distributed. As opposed to the existing literature based
on approximations and/or simulations, we formulate the problem
as one of finding the steady-state solution of a continuous-time
Markov chain with a block tridiagonal infinitesimal generator. To
find such solutions, we propose a numerically efficient and stable
algorithm based on block tridiagonal LU factorizations. We show
that exact blocking probabilities can be efficiently calculated
even for very large systems and rare blocking probabilities, e.g.,
systems with 256 wavelengths per fiber and blocking probabilities
in the order of 10â40. Relying on the stability and speed of the
proposed algorithm, we also provide a means of provisioning
wavelength channels and converters in optical packet/burst
switching systems
Shared-per-wavelength asynchronous optical packet switching: A comparative analysis
Cataloged from PDF version of article.This paper compares four different architectures for sharing wavelength converters in
asynchronous optical packet switches with variable-length packets. The first two architectures
are the well-known shared-per-node (SPN) and shared-per-link (SPL) architectures,
while the other two are the shared-per-input-wavelength (SPIW) architecture, recently
proposed as an optical switch architecture in synchronous context only, which is extended
here to the asynchronous scenario, and an original scheme called shared-per-output-wavelength
(SPOW) architecture that we propose in the current article. We introduce novel analytical
models to evaluate packet loss probabilities for SPIW and SPOW architectures in
asynchronous context based on Markov chains and fixed-point iterations for the particular
scenario of Poisson input traffic and exponentially distributed packet lengths. The models
also account for unbalanced traffic whose impact is thoroughly studied. These models are
validated by comparison with simulations which demonstrate that they are remarkably
accurate. In terms of performance, the SPOW scheme provides blocking performance very
close to the SPN scheme while maintaining almost the same complexity of the space
switch, and employing less expensive wavelength converters. On the other hand, the SPIW
scheme allows less complexity in terms of number of optical gates required, while it substantially
outperforms the widely accepted SPL scheme. The authors therefore believe that
the SPIW and SPOW schemes are promising alternatives to the conventional SPN and SPL
schemes for the implementation of next-generation optical packet switching systems.
2010 Elsevier B.V. All rights reserved
Exact performance analysis of a single-wavelength optical buffer with correlated inter-arrival times
Providing a photonic alternative to the current electronic switching in the backbone, optical packet switching (OPS) and optical bursts witching (OBS) require optical buffering. Optical buffering exploits delays in long optical fibers; an optical buffer is implemented by routing packets through a set of fiber delay lines (FDLs). Previous studies pointed out that, in comparison with electronic buffers, optical buffering suffers from an additional performance degradation. This contribution builds on this observation by studying optical buffer performance under more general traffic assumptions. Features of the optical buffer model under consideration include a Markovian arrival process, general burst sizes and a finite set of fiber delay lines of arbitrary length. Our algorithmic approach yields instant analytic results for important performance measures such as the burst loss ratio and the mean delay
Queueing Models Performance Analysis in Optical Switching Network Nodes
In optical switching networks, queueing models are often used for modeling, analyzing, and evaluating the performance of switching nodes. These models determine the number of optical packets in the switch and how quickly the switch can serve the traffic. This paper examines the numerical performance of optical switching nodes under various queuing models and simulates a modeling system using the OPNET modeler simulation tool. The study estimates the expected average number of optical packets, the probability of packet loss, and the waiting delay time in an optical switch under different loads and wavelength channels.The study estimates the expected average number of optical packets, the probability of packet loss, and the waiting delay time in an optical switch under different loads and wavelength channels.The study estimates the expected average number of optical packets, the probability of packet loss, and the waiting delay time in an optical switch under different loads and wavelength channels
Performance study of asynchronous/ synchronous optical burst/ packet switching with partial wavelength conversion
Cataloged from PDF version of article.Wavelength conversion is known to be one of the most effective methods for
contention resolution in optical packet/burst switching networks. In this thesis,
we study various optical switch architectures that employ partial wavelength
conversion, as opposed to full wavelength conversion, in which a number of converters
are statistically shared per input or output link. Blocking is inevitable
in case contention cannot be resolved and the probability of packet blocking is
key to performance studies surrounding optical packet switching systems. For
asynchronous switching systems with per output link converter sharing, a robust
and scalable Markovian queueing model has recently been proposed by Akar and
Karasan for calculating blocking probabilities in case of Poisson traffic. One of
the main contributions of this thesis is that this existing model has been extended
to cover the more general case of a Markovian arrival process through
which one can study the impact of traffic parameters on system performance.
We further study the same problem but with the converters being of limited range type. Although an analytical model is hard to build for this problem, we
show through simulations that the so-called far conversion policy in which the
optical packet is switched onto the farthest available wavelength in the tuning
range, outperforms the other policies we studied. We point out the clustering
effect in the use of wavelengths to explain this phenomenon. Finally, we study a
synchronous optical packet switching architecture employing partial wavelength
conversion at the input using the per input line converter sharing. For this architecture,
we first obtain the optimal wavelength scheduler using integer linear
programming and then we propose a number of heuristical scheduling algorithms.
These algorithms are tested using simulations under symmetric and asymmetric
traffic scenarios. Our results demonstrate that one can substantially reduce the
costs of converters used in optical switching systems by using share per input
link converter sharing without having to sacrifice much from the low blocking
probabilities provided by full input wavelength conversion. Moreover, we show
that the heuristic algorithm that we propose in this paper provides packet loss
probabilities very close to those achievable using integer linear programming and
is also easy to implement.DoÄan, KaanM.S
Simulation and analytical performance studies of generic atm switch fabrics.
As technology improves exciting new services such as video phone become possible and economically viable but their deployment is hampered by the inability of the present networks to carry them. The long term vision is to have a single network able to carry all present and future services. Asynchronous Transfer Mode, ATM, is the versatile new packet -based switching and multiplexing technique proposed for the single network. Interest in ATM is currently high as both industrial and academic institutions strive to understand more about the technique. Using both simulation and analysis, this research has investigated how the performance of ATM switches is affected by architectural variations in the switch fabric design and how the stochastic nature of ATM affects the timing of constant bit rate services. As a result the research has contributed new ATM switch performance data, a general purpose ATM switch simulator and analytic models that further research may utilise and has uncovered a significant timing problem of the ATM technique.
The thesis will also be of interest and assistance to anyone planning on using simulation as a research tool to model an ATM switch
A method for analyzing the performance aspects of the fault-tolerance mechanisms in FDDI
The ability of error recovery mechanisms to make the Fiber Distributed Data Interface (FDDI) satisfy real-time performance constraints in the presence of errors is analyzed. A complicating factor in these analyses is the rarity of the error occurrences, which makes direct simulation unattractive. Therefore, a fast simulation technique, called injection simulation, which makes it possible to analyze the performance of FDDI, including its fault tolerance behavior, was developed. The implementation of injection simulation for polling models of FDDI is discussed, along with simulation result
Retrial Queuing Models of Multi-Wavelength FDL Feedback Optical Buffers
Cataloged from PDF version of article.Optical buffers based on Fiber Delay Lines (FDL) have been proposed for contention resolution in optical packet/burst switching systems. In this article, we propose a retrial queuing model for FDL optical buffers in asynchronous optical switching nodes. In the considered system, the reservation model employed is of post-reservation type and optical packets are allowed to re-circulate over the FDLs in a probabilistic manner. We combine the MMPP-based overflow traffic models of the classical circuit switching literature and fixed-point iterations to devise an algorithmic procedure to accurately estimate blocking probabilities as a function of various buffer parameters in the system when packet arrivals are Poisson and packet lengths are exponentially distributed. The proposed algorithm is both accurate and fast, allowing one to use the procedure to dimension optical buffers in next-generation optical packet switching systems
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