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Reliability in optical access networks is becoming a crucial issue for both operators and users due to the enormous increase of capacity and the importance of uninterrupted access to network services. Consequently, the growing number of users requesting penalties for connection interruptions is motivating for investing in protection mechanisms in fiber access networks. The investments involved depend on several aspects such as technology and covered area (population density, distance, type of users, etc.). Moreover, the passive optical network is considered one of the most beneficial fiber access solutions from the capital expenditures point of view; in particular, we are witnessing a wide deployment of TDM PONs. Keeping in mind that cost is a major issue in the access part of the network, in this article we propose a cost-efficient way to provide protection in a TDM PON considering different deployment scenarios in respect to population density in the access network area. The cost efficiency is obtained by taking advantage of investment cost reduction caused by sharing the same duct by both working and protection fibers. In order to evaluate the investment associated with the deployment of the proposed protection schemes, we take into account three different approaches: provide protection in the access network from the beginning, invest initially on an unprotected architecture keeping in mind a future upgrade with protection resources, and roll out an unprotected access network and, if needed in the future, invest in deployment of protection resources. The cost parameters considered in this article include investment in the infrastructure and installation, as well as the operational expenditures associated with failure reparation and service interruption penalties. Our results confirm that the proposed reliable PON architectures can achieve significant reduction of service interruption at very low increase in investment cost, leading to a great decrease of the tot- l cost of ownership. Finally, some useful guidance for cost-efficient deployment of protection in fiber access networks is provided along with a sensitivity study to point out the key cost factors.