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dc.contributor.authorYang, Shuna
dc.date.accessioned2016-01-11T12:58:32Z
dc.date.available2016-01-11T12:58:32Z
dc.date.issued2015
dc.identifier.isbn978-82-326-1003-7
dc.identifier.issn1503-8181
dc.identifier.urihttp://hdl.handle.net/11250/2373275
dc.description.abstractThe advance in wavelength-division multiplexing (WDM) technology, which propagates closer to the network edge, enables the proliferation of applications with very high bandwidth and stringent performance requirements. However, today’s core networks, which mainly employ electronics for bulk processing and switching, eventually will become strained in both capacity and flexibility. The introduction of optical technologies in switching functions is a major evolution of core network. To relieve electronics switching, optical concepts like wavelength, waveband, and even fiber switching were developed and are currently introduced, e.g. by reconfigurable optical add-drop multiplexers (i.e. ROADM) and all-optical cross-connects (i.e. OXC). Optical switching methods have many distinct advantages compared with electrical switches: removing the expensive Optical-Electronic-Optical (OEO) conversion; providing high switching speed; benefiting environment with reduced power consumption; being independent with protocol and bit rates of the network. However, the clear and concrete solution of the switching architecture for the next generation optical networks has not been decided. In this thesis, a switching architecture named 3- Level-Integrated-Hybrid-Optical-Network (i.e. 3LIHON) is introduced as a potential candidate for the next-generation optical networks. Its virtue is related to the combination of merits of three different switching paradigms, which have different switching granularities. Accordingly three different traffic transport types (i.e., service classes) are transmitted on the same wavelength in a time-interleaved way. Thus, 3LIHON network can utilize the network resources efficiently while supporting a wide range of service classes with different service demands. 3LIHON concept is first proposed in proceedings of international conference IEEE GLOBECOM in 2011. Its novel concept opens wide variable research scenarios, ranging from the architecture realization and implementation (e.g. the detailed switching subsystem architectures definition and the respective working principles), to performance and availability evaluation (e.g. the performance metrics of each service class under the employed working principles and the architecture), as well as overall network architecture cost and power consumption analysis. The 3LIHON concept is the starting point of this PhD thesis. This thesis focuses on three research directions based on 3LIHON concept: first is the 3LIHON subsystem architecture design; second is the performance evaluation of the considered architecture; third is the performance modelling of employed working principles inside 3LIHON network (e.g. the preemptive scheduling which is widely used inside 3LIHON network-queue scheduling and part of output contention resolution mechanism). The ten included papers respond to these three directions and form the main contributions of this thesis. Among these contributions three concrete topics are treated in this thesis, i.e. the architecture design of 3LIHON edge node, OPS subsystem definition and improvement, the scheduling algorithm inside 3LIHON network and the respective performance modelling. The 3LIHON concept defines three service classes which are served by different switch subsystems: Guaranteed Service Type (i.e. GST); Statistically Multiplexing/Real-Time service type (i.e. SM/RT); Statistically Multiplexing/Best- Effort service type (i.e. SM/BE). GST service, which covers high real-time and bandwidth demands applications, is handled by OXC. OXC is the best choice for large scale high performance demands applications, due to its resource reservation and monopoly. By being handled by OXC, the strict performance of GST service can be guaranteed. SM/RT service, corresponding to very low bandwidth but very high real time demands applications, is switched by OPS equipped with limited or no buffer, due to its high switching speed and extremely short delay time. SM/BE service, which covers low real time demands applications, is served by EPS (i.e. electronic packet switching) which employs electronic buffers to reduce the respective packet loss as much as possible. However, how to map the incoming traffic into the three predefined service classes, which is operated by 3LIHON edge node, is not given by 3LIHON concept. Thus the first research topic of this PhD thesis is to design the 3LIHON edge node. The respective architecture (e.g. how to add up the traffic into 3LIHON network) and detailed working principles (e.g. the assembly algorithm of the GST traffic, the queueing scheduling for each buffer subsystem and the output contention resolution mechanism) are given in this thesis. The proposed architecture employs multiple electronic buffers to add up the local traffic into 3LIHON network whereas whether the cross traffic go through the electronic buffers depends on the service type. For GST, which is transmitted in circuit switched mode, no contention exists between local and transit GST traffic. Thus only the local GST traffic goes through the electronic buffers. We introduce the MBMAP (e.g. Max-Burstlength-Max-Assembly-Period) assembly algorithm to produce the GST burst. For SM/RT, which is very sensitive to packet delay and packet loss, we give the high priority to transit SM/RT traffic which is not buffered. The local SM/RT traffic goes through very limited electronic buffers in the 3LIHON edge node to reduce the packet loss introduced in the switch input. For SM/BE, which has high tolerance toward delay time, the sufficient size electronic buffers are employed in edge node to reduce its packet loss. For the switch output, where three service classes compete for the same wavelengths, the hierarchical contention resolution mechanism is applied. The GST service has the non-preemptive priority over SM/RT service, whereas both GST and SM/RT have preemptive priority over SM/BE service. For the performance evaluation of this proposed edge node architecture, six source types and two traffic types are applied to model the traffic inside the network as realistic as possible. This thesis mainly applies Demos/Simula to execute the simulations. The results showed that the proposed 3LIHON edge node architecture provides desirable performance for each service class. The detailed architecture and parameters’ design guidelines are given according to the results. The second topic in this thesis is the OPS subsystem definition. For 3LIHON network, the OPS subsystem is mainly used for switching very high real-time and low bandwidth demand SM/RT traffic. Thus the potential OPS candidate should have no/limited buffers to reduce the introduced delay. And the economic cost of OPS (e.g. the small physic size and the mature optical components) should be made as cheap as possible due to its extremely low requirement of throughput. Till now a lot of OPS architectures have been proposed. However, most of them focus on the packet contention resolution, fast packet switching and QoS. Not much attention is paid regarding the maturity of optical components and the corresponding economic cost, which are also major issues for the OPS subsystem of 3LIHON network. In order to achieve the best OPS candidate, we first evaluate the existing OPS architectures. Among them, the well-known OPS architecture equipped with limited range wavelength converters (i.e. OPS-LRWC) attracts research efforts. Compared with the general OPS with full wavelength converters (i.e. OPS-FWC), it is more promising due to its smaller physical size, less economic cost and easier implementation. To evaluate its performance, two separate Markov models are built to evaluate the packet loss of OPSLRWC under different network scenarios. The upper and lower packet loss values are derived directly by these two models. The results show that these two models provide desirable packet loss bounds for OPS-LRWC, independent of the employed conversion policies. Furthermore, the applicability of the proposed models depends on the normalized system load, the conversion range of the LRWCs, and the employed conversion policy. In addition, the results show that the packet loss decreases as the conversion range increases. However, different from the synchronous OPS networks, which have a threshold of the conversion range for limiting the performance improvement, no choice of the best wavelength conversion range exists in the asynchronous OPS networks. In order to find the best candidate, we also propose a novel OPS architecture equipped with input concentrators before the switch fabric. Multiple cascaded fiber delay lines are used to build the input concentrators, the main function of which is to aggregate the incoming traffic from same wavelength into only one input link of switch fabric. Accordingly, the physical size and the respective economic cost of OPS are reduced significantly, whereas the link utilization increases dramatically. This architecture is designed special for very low incoming traffic scenario, e.g. 3LIHON network scenario. However, the employment of input concentrators would introduce the additional delay time in the switch input. In order to evaluate its performance, we build a one-dimensional Markov model according to the packet departure process from the input concentrator. The packet loss and mean packet delay introduced by input concentrators can be given by Markov model directly. The results show that the additional delay time is far less than the tolerant delay time. Meanwhile a learning curve model is introduced to analyze its economic cost, which is expressed as a function of time. The proposed OPS architecture is firstly compared with OPS without input concentrators based on AWG, and then compared with the OPSLRWC architectures based on B&S switch fabric (i.e. broadcast and select). Both results show that the proposed OPS architecture is much cheaper while providing same performance as these architectures. Some more works has been done to improve the proposed OPS architecture, in which the input concentrators dominate the performance of whole OPS node. We generalize the input concentrators as multiple input single output delay-line optical buffers. A novel modeling approach is developed to denote the delay time evolution of each new arrival to the buffer. Both fixed (all packets’ length is constant) and variable length (the packet length follows n.e.d. distribution) incoming traffic are considered. This approach is validated by simulations under different network scenarios. The results show that the basic FDL length is a very important parameter for the buffer performance. The optimal FDL length value is dominated by incoming traffic load and the packet length (mean packet length for case-n.e.d. incoming packets), and independent of the buffer size offered by buffer. These results validate that setting the FDL length same as the packet length is not the best choice for delay-line buffers. Meanwhile, this approach gives the guidelines for designing the optical buffer with the best performance under different scenarios. By adjusting the basic FDL length value, the performance of the whole OPS node can be improved significantly. It is noticeable that all results achieved from this topic can not only be used in 3LIHON network, but also very useful for general optical network scenarios, e.g. the proposed OPS architecture can widely be employed in the access networks with low entrance traffic; the evaluation results from the proposed input concentrators can generally be used for improving the general optical networks with such delay-line buffers. The third topic of this thesis is the evaluation of preemptive scheduling, which is widely used in optical networks as service differentiation. In 3LIHON network, the hierarchical contention resolution mechanism is employed at the switch output, in which both of GST and SM/RT classes have the preemptive priority over SM/BE. Meanwhile, the preemptive scheduling is generally used as contention resolution in pure OPS/OBS networks. Thus in this thesis we pay special attention to study the preemptive scheduling. Its performance and operations are evaluated in both optical networks and the general multi-service systems. Three included papers (i.e. P6, P7 and P8) contribute to this topic. For performance modeling, a novel approximation model-hierarchical Markov model is proposed. According to the priority of each class, the model is built as multiple levels. Each level presents all the transmission states of the respective service class. When calculating the blocking probabilities, conditional probability principles are used to weigh and sum contributions from each one-dimensional Markov chain in each level. This model only needs to increase the number of levels when modeling the larger system with more classes, thus it shows excellent extensibility. Compared with the general analytical modeling, which use the multi-dimensional Markov model to analyze the small system with less classes and resources, the proposed model has several major advantages: applicability of analyzing the general multi-service systems, closed-form expressions of the blocking probabilities and the significantly decreased computational complexity. Furthermore, this thesis validates the accuracy of the proposed hierarchical model. For the service class with highest priority, this model always provides the accurate packet loss. However for other services, this model provides the satisfactory approximate results. The respective discrepancy decreases as the relative load allocation of all higher service classes (compared with the studied service class) decreases. In addition, it is noticeable that, all results obtained from the proposed hierarchical Markov model are applicable for the general multi-service systems with preemptive schedulingnb_NO
dc.language.isoengnb_NO
dc.publisherNTNUnb_NO
dc.relation.ispartofseriesDoctoral thesis at NTNU;2015:173
dc.titlePerformance Evaluation and Improvement of Next-generation Optical Switching Architecturenb_NO
dc.typeDoctoral thesisnb_NO
dc.subject.nsiVDP::Technology: 500::Information and communication technology: 550::Telecommunication: 552nb_NO


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