Browsing by Subject "Packet switching."

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Open Access
Flow control and service differentiation in optical burst switching networks
(2005) Boyraz, Hakan
Optical Burst Switching (OBS) is being considered as a candidate architecture for the next generation optical Internet. The central idea behind OBS is the assembly of client packets into longer bursts at the edge of an OBS domain and the promise of optical technologies to enable switch reconfiguration at the burst level therefore providing a near-term optical networking solution with finer switching granularity in the optical domain. In conventional OBS, bursts are injected to the network immediately after their assembly irrespective of the loading on the links, which in turn leads to uncontrolled burst losses and deteriorating performance for end users. Another key concern related to OBS is the difficulty of supporting QoS (Quality of Service) in the optical domain whereas support of differentiated services via per-class queueing is very common in current electronically switched networks. In this thesis, we propose a new control plane protocol, called Differentiated ABR (D-ABR), for flow control (i.e., burst shaping) and service differentiation in optical burst switching networks. Using D-ABR, we show with the aid of simulations that the optical network can be designed to work at any desired burst blocking probability by the flow control service of the proposed architecture. The proposed architecture requires certain modifications to the existing control plane mechanisms as well as incorporation of advanced scheduling mechanisms at the ingress nodes; however we do not make any specific assumptions on the data plane of the optical nodes. With this protocol, it is possible to almost perfectly isolate high priority and low priority traffic throughout the optical network as in the strict priority-based service differentiation in electronically switched networks. Moreover, the proposed architecture moves the congestion away from the OBS domain to the edges of the network where it is possible to employ advanced queueing and buffer management mechanisms. We also conjecture that such a controlled OBS architecture may reduce the number of costly Wavelength Converters (WC) and Fiber Delay Lines (FDL) that are used for contention resolution inside an OBS domain.
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.