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In time division, multiple access (TDMA)-based passive optical network (PONs), a dynamic bandwidth assignment (DBA) is necessary for efficient utilization of the available bandwidth of the upstream link. An efficient DBA scheme can improve the upstream performance of a traffic class of an ONU in two ways. First, it can increase the bandwidth assignment to it by efficiently utilizing the available bandwidth. Secondly, it can reduce the channel and frame idle time by increasing the polling frequency and by assigning extra surplus bandwidth not used by the other ONUs. Many DBA schemes have been reported for both ITU PONs (GPON and XGPON) and IEEE PONs (EPON and 10 G EPON). In this study, we explain the impact of DBA scheme on the upstream performance of PON and then do a thorough survey of both PON standards, categorize the DBA schemes and review them critically. Based on the literature review we also give our opinion on the most suitable DBA scheme for both type PONs on the basis of upstream delays, frame loss and bandwidth utilization efficiency. [ABSTRACT FROM AUTHOR]

The time division multiplexed (TDM) based passive optical networks like GPON/XGPON and EPON/10G-EPON use broadcast mechanism for downstream (DS) communication. This results in any DS frame being received and processed by all optical network units (ONUs), leading to significant processing energy wastage. Specifically, the ITU compliant PONs (GPON/XGPON) frame structure further aggravates this problem due to its inefficient frame structure and synchronous nature which requires sending of DS frames every 125 μs. This frame structure requires an ONU to completely process every DS frame completely, even if it is not destined for it. The bit interleaved PON (Bi-PON) resolves this problem by changing the frame structure to a bit interleaved pattern and introduce a decimator unit that enables an ONU to tune to its concerned bits only. However, due to additional hardware requirement, this solution is not applicable to current ONU architecture. Consequently, this study presents a processing efficient version of GPON frame that helps an ONU to identify an unrelated DS frame at its start and thus discard it without complete processing. A processing efficient strategy for the medium access layer (MAC) processor of an ONU is also presented. The simulation results show a processing energy saving of 88%, 89% and 89.47% with proposed frame structure for a split ratio of 16, 32 and 64 respectively. [ABSTRACT FROM AUTHOR]

For an efficient utilization of the upstream bandwidth in passive optical network, a dynamic bandwidth assignment mechanism is necessary as it helps the service providers in provisioning of bandwidth to users according to the service level agreements. The scheduling mechanism of existing schemes, immediate allocation with colorless grant and efficient bandwidth utilization (EBU), does not assign the surplus bandwidth to a specific traffic class and only divides it equally among the optical network units (ONUs). This results in overreporting of ONU bandwidth demand to the optical line terminal and causes wastage of bandwidth and increase in delays at high traffic loads. Moreover, the EBU also assigns the unused bandwidth of lightly loaded ONU queues to the overloaded queues through an Update operation. This Update operation has a flaw that it borrows the extra bandwidth to a queue in the current service interval, if the queue report is higher than its service level agreement and refunds in next service interval. This borrow-refund operation causes reduced bandwidth allocation to the lower priority classes and increases their delay and frame loss. This study improves both these weaknesses. The simulation results show that the proposed scheme uses bandwidth efficiently and reduces mean upstream delay of type-2 (T2) traffic class by 38% and type-3 (T3) up to 150% compared to immediate allocation with colorless grant at a cost of up to 10% higher delay for T2. However, T4 performance improves by 400% compared to EBU with slight increase in delay for T2 traffic class. Overall, it shows a balanced performance for all the traffic classes and minimizes the bandwidth waste per cycle as well as the frame loss rate. [ABSTRACT FROM AUTHOR]