The increased propagation delay of future long-reach passive optical networks (LR-PONs) may lead to a significantly increased idle time and delay if optical network units (ONUs) use conventional report-grant mechanisms. Sophisticated and efficient bandwidth allocation mechanisms are required to cope with the imposed propagation delay in LR-PONs. In this study, we evaluate three dynamic bandwidth allocation (DBA) frameworks in terms of frame (packet) delay; namely, we consider conventional (interleaved) polling for traditional PON and two recently introduced scheduling paradigms for next generation LR-PON, i.e., multi-thread polling (MT-P) and real-time polling (RT-P). We enhance MT-P and RT-P by applying the just-in-time framework. Next, we provide an analytical framework for evaluating the end-to-end frame delay in our enhanced MT-P and RT-P frameworks. We compare their performance with conventional polling and double-phase polling and investigate their shortcomings and advantages in an LR-PON setting. The simulation results closely match the analysis for this framework. Also, our results indicate that RT-P significantly reduces frame delay in LR-PONs compared to MT-P and conventional polling frameworks.

Designing low latency polling schemes is one of the most important parts for passive optical networks (PONs), particularly for long-reach PONs (LR-PON) which suffer from long propagation delays. Sophisticated and efficient bandwidth allocation mechanisms are required to cope with the imposed transmission delay in LR-PONs. In this work, we evaluate three dynamic bandwidth allocation methods in terms of transmission delay. Namely, we consider conventional or interleaved polling for traditional PON and two recently introduced scheduling paradigms for next generation LR-PON, i.e., multi-thread polling (MT-P) and real-time polling (RT-P). We examine various flavors of each scheduling method and investigate their shortcomings and advantages in a LR-PON setting. Furthermore, we provide an analytical framework for obtaining packet delay in an enhanced version of RT-P method. The simulation results highly match the analysis for this framework. Also, our results indicate that RT-P method significantly reduces frame delay in LR-PONs compared to MT-P and conventional polling methods.

Dynamic bandwidth allocation and grant scheduling are among the major issues in the design of passive optical networks. In this paper, we investigate the problem of optimal scheduling and bandwidth allocation in next generation 10GEPON coexisting with 1G WDM-PONs. We first propose a network architecture for providing this coexistence. Then, we derive an ILP model for offline joint scheduling and bandwidth assignment for 10G-TDM and 1G-WDM ONUs. In order to address the scalability of the ILP model, we introduce a Tabu Search based heuristic for obtaining near optimal solutions while the computation time is remarkably reduced. We further explore the tradeoff which exists in terms of delay, scheduling length, and channel utilization, when separate or the same DBA modules are used for 1G- and 10G-ONUs.

Survivability is a key issue in the design of optical mesh networks. Various survivability schemes have been introduced among which p-cycle has been attracting quite a lot of attention because of its fast and efficient protection capability. The concept of p-cycle was later generalized to pre-cross-connected trails or p-trails, by noting to the fact that providing pre-cross-connected protection paths and obtaining fast restoration does not require a cyclic structure. In this paper, we investigate the capability of p-trails in protecting traffic demands in a mesh-based survivable network. By taking the sharing capability of p-trails into account, we introduce optimization models to verify the remarkable efficiency of p-trails. We derive two ILP models for survivable network design using p-trails. In our first model, the optimal solution is obtained from a candidate set constructed by exhaustive enumeration of all simple trails. We observe that the size of our ILP model, and therefore the computation time, become prohibitively large making the model unpractical for larger network instances. Therefore, to overcome this scalability issue, we develop a better model for this complex optimization problem using a primal-dual decomposition of the original problem based on the column generation (CG) optimization method. Our developed design approach is shown to be very scalable, as opposed to other prior p-trail design methods; further, we show that p-trails are more efficient than p-cycles in terms of resource redundancy in the network.

Network survivability is a key design issue for optical transport mesh networks. Various survivability schemes have been introduced among which p-cycle has (and continues) attracted quite a lot of attention because of its fast and efficient protection capabilities. The concept of p-cycle has been generalized to pre-cross-connected trails, or p-trails, by exploiting the fact that providing pre-cross-connected protection paths and obtaining fast restoration do not necessarily require a cyclic structure as in p-cycles. In this paper, we investigate the benefits and sharing capabilities of p-trails and observe that non-simple p-trails and p-cycles can be built from merging simple trails. We derive two ILP models for survivable network design using p-trails. Our first design model is a simple ILP whose optimal solution relies on the exhaustive enumeration of all simple trails in the network. We observe that the size of our ILP model, and therefore the computation time, become prohibitively large making the model unpractical for larger network instances. Therefore, to overcome this scalability issue, we develop an enhanced model for this complex optimization problem using the column generation (CG) decomposition technique. Our developed design approach is shown to be very scalable, as opposed to other prior p-trail design methods; further, we show that p-trails are more efficient than p-cycles in terms of protection resource redundancy in the network.

Bandwidth allocation and transmission grant scheduling are problems of particular interests to multichannel Passive Optical Networks (PONs). While a number of studies have been carried out on each of these subproblems separately, to the best of our knowledge a study on the joint problem has been lacking. In this paper, we investigate the joint problem of bandwidth allocation and transmission grant scheduling in multichannel optical access networks using a scheduling theoretic approach. We formulate the problem as an ILP model and compare it with the sequential model presented in pervious work. Our experiments declare that the joint scheduling and sizing algorithm achieves a reduction of up to 28% in scheduling cycle length when compared to the non-joint models. Since the model has shown to be very hard to solve, except for small sized network instances, we introduce a Tabu search heuristic for the joint problem that provides near optimal solutions in significantly shorter times. We also illustrate that the choice of buffer size of ONUs has a critical rule in the performance of our joint scheduling and bandwidth allocation solutions.