1. Introduction

Exponential growth in Internet traffic has significantly increased the demand for high bandwidth connectivity at both business and residential premises. Internet service providers are deploying passive optical network (PON) at the access domain to provide the required capacity

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in terms of reach, bandwidth, and the number of subscribers. In PON, all services are originated from an optical line terminal (OLT) at the central office (CO). End-face of the OLT is connected to a 15–20 km feeder fiber (FF) that extends the network toward the subscriber premises called optical distribution network (ODN). Remote node (RN) receives the FF at ODN, which houses a 1 : N bidirectional passive optical coupler (POC). N output ports from the POC are fed into short-branched distribution fibers (DFs) that connect the RN to individual optical network unit (ONU) transceiver modules [1].

PON has emerged as a promising candidate to resolve the last-mile bottle, owing to its significant advantages like:


With the rapid increase in PONs capacity, fault detection and restoration at satisfactory costs have turned the network reliability to a new challenge for Internet service providers. Each subscriber is interested in seamless reception of maximum bandwidth at minimum possible cost. However, the conventional PON architecture has limited protection, which results in significant data loss at the event of failure in optical components including OF medium. Therefore, it is imperative to devise an architecture, which is capable of maintaining a seamless flow of upstream and downstream traffic at required capacity and acceptable costs for a common end subscriber [1, 2].

Two techniques are readily adapted to provide fault detection and restoration in PON, namely pre-planned and dynamic protection. The latter relies on fault detection and restoration through diagnosis at the higher levels and dynamically allocates resources at the event of failure. Such technique requires more time for traffic restoration between OLT and ONU modules, as upper layer recovery techniques usually utilize routing tables, topology recalculations, and slow convergence time. Yet there is no guarantee for fault restoration at the physical layer [1–3]. Therefore, for the facilitation of an effective and prompt fault detection and restoration, it is highly desirable to provide protection measures at the optical layer.

Pre-planned protection utilize an optical-layer approach by providing dedicated backup paths for components including OF medium. This type of protection is planned at the network design phase, owing to the fact that topology of PON remains same, and the proposed solution can address fault restoration at both feeder and ODN. This type of protection provides high reliability at minimum recovery time in the event of failures at both optical components and OF medium. However, path and resources duplication significantly elevates the CAPEX at the network deployment phase [4, 5]. Therefore, it is imperative to encompass the following considerations while designing a pre-planned protection architecture.
