Novel Architectures to Enhance QoS in Long-Reach Passive Optical Networks

Future access networks need to withstand high traffic demand of users as well as to ensure certain degree of reliability to data transmission against network failures. Long-reach passive optical networks (LR-PONs) are being envisioned as one of the best emerging future networks due to their capability to offer very high data rate at low cost. In a LR-PON, an optical line terminal (OLT) in central office is used as a master node to control upstream and downstream traffic from/to the users. The OLT allocates bandwidth to users for their upstream traffic transmission through executing a dynamic bandwidth allocation scheme. However, traffic congestion occurs when users need more than the allocated bandwidth due to their high traffic load in some time periods of a day. The high traffic congestion severely increases traffic delay, thereby degrading quality of service (QoS) performance in the network. Since, LR-PONs carry high traffic, backup OLTs may need to be used to facilitate service recovery in case of failure of any working OLT. A backup OLT remains idle until a failure occurs. In this paper, we explore two novel architectures wherein we utilise the idle backup OLTs to serve the users requesting for high bandwidth and providing protection to users to ensure certain degree of reliability to traffic in case of any failure. Our simulation results show that the proposed architectures minimize the traffic delay in congestion hours by efficiently utilising the backup OLTs; they also enhance reliability to traffic transmission by providing protection against failures, thereby significantly improving QoS performance in the network.