Browsing by Subject "Wavelength conversion"

Now showing 1 - 8 of 8

Open Access
Effect of burst length on loss probability in OBS networks with void-filling scheduling
(2006) Kamçı, Ahmet Kerim
Optical burst switching (OBS) is a new transport architecture for the next generation optical internet infrastructure which is necessary for the increasing demand of high speed data traffic. Optical burst switching stands between optical packet switching, which is technologically difficult, and optical circuit switching, which is not capable of efficiently transporting bursty internet traffic. Apart from its promising features, optical burst switching suffers from high traffic blocking probabilities. Wavelength conversion coupled with fiber delay lines (FDL) provide one of the best means of contention resolution in optical burst switching networks. In this thesis, we examine the relation between burst loss probability and burst sizes for void filling scheduling algorithms. Simulations are performed for various values of the processing and switching times and for different values of wavelengths per fiber and FDL granularity. The main contribution of this thesis is the analysis of the relationship between burst sizes and processing time and FDL induced voids. This in turn creates a better understanding of the burstification and contention resolution mechanisms in OBS networks. We show that voids generated during scheduling are governed by the FDL granularity and the product of the per-hop processing delay and residual number of hops until the destination. We also show that differentiation between bursts with different sizes is achieved for different network parameters and a differentiation mechanism based on burst lengths is proposed for OBS networks.
Open Access
On dynamic wavelength assignment in WDM optical networks
(Springer, 2001) Alanyalı, Murat; Ruan, L.; Du, D. Z.
Optical fiber has been used as the physical medium for high rate data transmission since late 1960s. Early applications of optical fiber communications modulated data onto a single optical carrier frequency that is commonly referred to as a wavelength. The carried data rate is therefore limited by the speed of electronics that generate the signal, thereby grossly underutilizing the tens of THz of useful bandwidth available on the fiber[1]. The Wavelength Division Multiplexing (WDM) technology now allows multiplexing everal optical carriers on the same fiber, opening up the available potential. Current deployments of WDM are based on point-to-point links. This entails demodulating the optical signal at each switching node and carrying out switching electronically. Remarkable increase in the carried data rates due to the WDM technology make these switches inherent bottlenecks in the network. One promising approach to solve this problem is optical switching which entails switching entire wavelengths without any electronic processing.
Open Access
Performance of WDM transport networks
(Institute of Electrical and Electronics Engineers, 1998-08) Karasan, E.; Ayanoglu, E.
Wavelength division multiplexed point-to-point transport is becoming commonplace in wide area networks. With the expectation that the next step is end-to-end networking of wavelengths (in the optical domain without conversion to electronics), there is a need for new design techniques, a new understanding of the performance issues, and a new performance evaluation methodology in such networks. This paper describes approaches to that end, summarizes research results, and points to open problems.
Open Access
Performance study of asynchronous/ synchronous optical burst/ packet switching with partial wavelength conversion
(2006) Doğan, Kaan
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.
Open Access
Rate-controlled optical burst switching for both congestion avoidance and service differentiation
(Elsevier, 2005) Boyraz, H.; Akar, N.
Optical Burst Switching (OBS) has recently been proposed as a candidate architecture for the next generation optical Internet. Several challenging issues remain to be solved to pave the way for the OBS vision. Contention arises in OBS networks when two or more bursts are destined for the same wavelength, and a wide variety of reactive contention resolution mechanisms have been proposed in the literature. One challenging issue in OBS is proactively controlling the traffic flowing through the OBS network so that the network does not stay in a persistent state of contention, which we call the congestion avoidance problem. Another challenging issue is the need for service differentiation, which is common today in electronically switched networks via the use of advanced buffer management and scheduling mechanisms. However, such mechanisms cannot be used in OBS networks due to the limited use, or total absence, of buffering. One of the popular existing approaches to service differentiation in OBS networks is the use of larger offset times for high-priority bursts which, however, increases the delays and may adversely affect application-level performance. In this paper, we propose a feedback-based rate control protocol for the control plane of the OBS network to both address the congestion avoidance and service differentiation issues. Using this protocol, the incoming traffic is dynamically shaped at the edge of the OBS network in order to avoid potential congestion in the burst-switched core. Moreover, the traffic shaping policies for the low and high priority traffic classes are different, and it is possible using the proposed protocol to isolate high-priority and low-priority traffic almost perfectly over time scales on the order of a few round-trip times. Simulation results are reported to validate the congestion avoidance and service differentiation capabilities of the proposed architecture. © 2006 Elsevier B.V. All rights reserved.
Open Access
Shared-per-wavelength asynchronous optical packet switching: a comparative analysis
(Elsevier, 2010-03-23) Akar, N.; Rafaelli, C.; Savi, M.; Karasan, E.
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.
Open Access
Simultaneous optical parametric oscillation and sum-frequency generation within a single crystal for converting 1064 nm into 627 nm
(IEEE, 2005-07) Figen, Z. Gürkan; Aytür, Orhan
We report a 1064-nm pumped optical parametric oscillator based on a single KTiOAsO4 crystal that simultaneously generates the sum frequency of the pump and signal wavelengths, providing a 627 nm output with a high conversion efficiency.
Open Access
Wavelength converter sharing in asynchronous optical packet/burst switching: an exact blocking analysis for markovian arrivals
(IEEE, 2006-12-11) Akar, N.; Karasan, E.; Doğan, K.
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 10−40. 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.