Controlling QoS in EPON-based FTTX access networks

Abstract

The Ethernet PON (EPON) is viewed by many as an attractive solution to deliver very high-speed broadband access and is widely deployed in some geographical areas. While downstream traffic is broadcast to all customers, the access of upstream traffic to the fiber has to be arbitrated in order to avoid collisions. This arbitration mechanism and more generally, bandwidth distribution and QoS Provisioning, have been left to the implementer. One solution is to enforce static Time Division Multiplexing Access (TDMA) between end-users. This however precludes an efficient usage of resources. Interleaved Polling with Adaptive Cycle Time (IPACT) is one of the earliest proposed schemes for Dynamic Bandwidth Assignment (DBA) in EPON and has been extensively used as a benchmark by many subsequent allocation schemes. In this paper, we first propose an analytical model which yields approximate values for mean queue length and mean packet delay in an EPON using IPACT with Gated Service (GS) scheme under the assumption of heterogeneous Poisson arrivals. We use the model to demonstrate that all users experiment performance degradation in case of local overload, thus showing the necessity of correcting somehow IPACT-GS in order to avoid this phenomenon. This is achieved by designing a control plane for EPON, which includes a priority based DBA together with a framework for enforcing Service Level Agreements (SLAs), and fairly sharing available resources. The proposed framework is easily configured (all the control being centralized at the OLT or in the backbone) while allowing the support of large varieties of services. It is shown to behave more efficiently than other QoS sensitive DBAs in the literature.