In a long-reach passive optical network (LR-PON), protection for optical network units (ONUs) against their distribution fiber (DF) failures is highly desirable to ensure uninterrupted Internet access to the associated users. In the distribution section of the LR-PON, shared-risk link groups (SRLGs) are formed by DFs due to sharing fiber cables and conduits. Most of the existing SRLG-aware DF protection schemes require residual bandwidth with ONUs. Therefore, they fail to provide protection to all ONUs under high reliability requirements (RRs) and result to be very cost-inefficient as well. We first propose a SRLG-aware reliability framework to compute the connection reliability of every ONU and joint reliability of every ONU-ONU pair and ONU-node pair. Thereafter, we propose two different SRLG-aware nonresidual bandwidth based partial protection schemes and their compatible architectures to provide partial DF protection to ONUs against SRLG failures to satisfy the given RR. Following the proposed schemes, we formulate two different integer linear programming (ILP) based optimization problems to set up backup connections by using backup DFs and other backup optical resources with the minimum protection cost. The proposed ILP-based protection planning models restrict the backup DF lengths to bound the propagation delay to satisfy the strict delay requirement for real-time applications. Since the proposed ILP-based models turn out to be computationally intractable for large network problems, we also propose two heuristic schemes that provide comparable results to that of the ILP-based models. We evaluate the performance of the proposed partial protection schemes with reference to the protection cost and total length of backup DFs (TLBDF). The exhaustive simulation results show that the proposed partial protection schemes not only satisfy high RRs, but also require a much lower protection cost, TLBDF, and optical power margin in comparison to the existing SRLG-aware protection schemes.

在长距离无源光网络 (LR-PON) 中，非常需要保护光网络单元 (ONU) 免受其分布光纤 (DF) 故障的影响，以确保相关用户不间断地访问互联网。在 LR-PON 的分布部分，由于共享光缆和管道，由 DF 形成共享风险链路组 (SRLG)。大多数现有的 SRLG 感知 DF 保护方案都需要 ONU 的剩余带宽。因此，它们无法在高可靠性要求 (RR) 下为所有 ONU 提供保护，并且成本效率也非常低。我们首先提出了一个 SRLG 感知的可靠性框架来计算每个 ONU 的连接可靠性以及每个 ONU-ONU 对和 ONU-节点对的联合可靠性。此后，我们提出了两种不同的基于 SRLG 感知的非剩余带宽的部分保护方案及其兼容架构，为 ONU 提供部分 DF 保护，防止 SRLG 故障，以满足给定的 RR。根据所提出的方案，我们制定了两个不同的基于整数线性规划 (ILP) 的优化问题，以使用备份 DF 和其他备份光资源以最小的保护成本建立备份连接。所提出的基于 ILP 的保护规划模型限制备份 DF 长度以限制传播延迟，以满足实时应用的严格延迟要求。由于提出的基于 ILP 的模型在计算上难以解决大型网络问题，因此我们还提出了两种启发式方案，它们提供了与基于 ILP 的模型相当的结果。我们参考保护成本和备份 DF (TLBDF) 的总长度来评估所提出的部分保护方案的性能。详尽的仿真结果表明，与现有的 SRLG 感知保护方案相比，所提出的部分保护方案不仅满足高 RR，而且需要低得多的保护成本、TLBDF 和光功率裕度。