Protection Architectures for WDM Passive Optical Networks

Introduction

Passive optical networks (PONs) are used to provide last mile connectivity, thereby fulfilling the rising bandwidth (BW) needs of home users and the industry (Lam, 2007). A PON is a point-to-multipoint network in which a single optical fiber supports high data rates while connecting multiple users. The components used along the transmission path are passive in nature, i.e. they do not consume any electrical power. This passive property of the network is considered as its biggest asset when compared to other networks which use active components. This significantly reduces the operational cost of the overall network by eliminating the need for running power cables alongside transmission cables. Current generation PONs support up to 64 customers spread over a distance of 20 Km from the central office. They support data rates of the order of Gbps. Factors such as energy efficiency, increased number of customers per central office port, unused bandwidth capacity of optical fibers and low-cost optical components employed in PON make it a better access network compared to others like WiMAX, Wi-Fi and traditional DSL based networks.

There are different PON types such as ATM PON defined in ITU-T G.983.1 (ITU-T, 1998, 2000), Broadband PON defined in ITU-T G.983.3 (ITU-T, 1998, 2001, 2002), Ethernet PON defined in IEEE 802.3ah (IEEE 802.3Ethernet in the First Mile Study Group, 2001), Gigabit PON defined in ITU-T G.984 (ITU-T, 2003), 10G-EPON defined in IEEE 802.3av and Wavelength Division Multiplexed (WDM) PON (Banerjee et al., 2005). A-PON refers to ATM PON wherein ATM is used as the signaling protocol. B-PON refers to broadband PON. Ethernet PON makes use of IEEE 802.3 Ethernet frames for data transmission and G-PON refers to gigabit PON where in the data rates are of the order of Gbps. APON, BPON, EPON and GPON use Time Division Multiple Access (TDMA) protocol for data transmission between the Optical Line Terminal (OLT) and the Optical Network Units (ONU). In TDM PON a power splitter (PS) acts as a remote node (RN), where each ONU is allocated a part of the total bandwidth available for the PON network. All the ONUs in the TDM PON network need to be time synchronized and the data rate of all the ONUs should also be the same. Such constraints are overcome by WDM PONs.