Protection to optical network units (ONUs) against failure of their distribution fibers (DFs) in a long-reach passive optical network (LR-PON) is highly desirable to provide uninterrupted internet services to the users. In practical network scenarios, DFs form shared-risk link groups (SRLGs). The existing SRLG-aware protection schemes depend on residual bandwidth of ONUs. Therefore, they are cost-inefficient and also fail to satisfy high reliability requirements (RRs). We for the first time propose a nonresidual bandwidth based partial protection scheme and related architecture to provide partial protection to ONUs against a single SRLG failure. Following the proposed scheme, we formulate an integer linear programming (ILP)-based optimization problem to provision backup DFs and network components for providing protection with the minimum protection cost. To meet the strict delay requirement for real-time applications, the proposed ILP model restricts the length of backup DFs to be employed to restore the traffic transmission. As the proposed ILP model becomes computationally intractable for large networks, we also propose a heuristic scheme that provides fairly close results to that of the ILP model. We assess the performance of the proposed partial protection scheme in terms of protection cost and total length of backup DFs (TLBDF). Through exhaustive simulation study we show that the proposed partial protection scheme not only satisfies high RRs but also requires much lower protection cost and TLBDF as compared to the existing SRLG-aware protection schemes.

为了向用户提供不间断的互联网服务，非常需要保护光网络单元（ONU）以防止其分布光纤（DF）在长距离无源光网络（LR-PON）中发生故障。在实际的网络场景中，DF形成了共享风险链接组（SRLG）。现有的SRLG感知保护方案取决于ONU的剩余带宽。因此，它们是成本低效的，并且也不能满足高可靠性要求（RR）。我们首次提出了一种基于非剩余带宽的部分保护方案和相关架构，以针对单个SRLG故障向ONU提供部分保护。按照拟议的方案，我们制定了一个基于整数线性规划（ILP）的优化问题，以提供备用DF和网络组件，从而以最低的保护成本提供保护。为了满足实时应用的严格延迟要求，提出的ILP模型限制了用于恢复流量传输的备用DF的长度。由于所提出的ILP模型在大型网络上变得难以计算，因此我们还提出了一种启发式方案，该方案提供的结果与ILP模型相当接近。我们根据保护成本和备用DF（TLBDF）的总长度来评估建议的部分保护方案的性能。