(A) novel energy saving mechanism for TDM passive optical networks

Abstract

Maximizing energy saving in Information and Communication Technology (ICT) becomes an important goal due to rise of energy price (operation expenditure) and environmental impact. Access networks consume significant portion of overall ICT energy consumption. This is principally because the access networks consist of a huge number of components (i.e. Customer Premises Equipment (CPE)).

TDM Passive Optical Networks (TDM-PONs) (e.g. Ethernet PON (EPON) and Gigabit-capable PON (GPON)) are promising access network technologies (in terms of data rate and energy consumption), and thus they have been widely deployed. Equipment of a TDM-PON are: Optical Line Terminal (OLT), Optical Network Unit (ONU), and passive splitter. In a TDM-PON, ONUs are placed at the CPE side which can support number of users

whereas, the OLT is placed at the central office of the service provider. The operation of a TDM-PON is point-to-multipoint network in which the OLT connects multiple ONUs via optical medium through passive splitter. The OLT plays the vital role as the master device and it controls multiple slave ONUs. The main role of the OLT is to assign upstream grant time to connected ONUs to send their traffic.

Most of the energy saving research efforts are centered on maximizing energy saving at ONUs. In this perspective, researchers from academia and industry are attracted to develop and propose energy saving techniques and protocols for ONUs in TDM-PONs. A widely used approaches to reduce an ONU's energy consumption are TRx sleep mode and Tx sleep mode mode. In TRx sleep mode, the transmitter and receiver of the fiber link in an ONU are turned \textit{`off'} and turned \textit{`on'} periodically. Whereas, Tx mode aims to power the transmitter \textit{`off'} in absence of upstream traffic while keeping the receiver always \textit{`on'}. Note that there is an overhead time for ONUs to turn \textit{`on'}/\textit{`off'} its transceiver. The OLT uses an algorithm to decide sleep interval length. However, predicting proper sleep interval lengths is very difficult due to the bursty nature of traffic in access networks.

Recent IEEE and ITU-T standards for TDM-Passive Optical Network (TDM-PON) with sleep mode recommend that the Optical Line Terminal (OLT) in a TDM-PON should be in charge of invoking an Optical Network Units (ONU) to move into sleep state in absence of frames. It is considered that, on upstream frame arrival, a sleeping ONU can leave sleep state, in which an ONU turns off its transmitter or both transmitter and receiver immediately, prior to its assigned sleep interval length. In this dissertation, we refer to this approach as immediate early wake-up (IMEW). According to the standards, the OLT may or may not allow an ONU to trigger early wake-up function (EWF) on upstream frames arrival. If the OLT does not allow EWF (not support early wake-up (NSEW)), an ONU should stay in sleep state during its assigned sleep duration and buffer all the upstream frames while it is in this state. In IMEW, upstream frames experience small delay but ONU's energy consumption increases remarkably. Conversely, in NSEW, an ONU consumes less energy compared to IMEW at the price of increasing upstream frame delay and possibility of its buffer overflow. In this dissertation, the limitations of IMEW and NSEW have motivated us to propose a novel Early Wake-up Decision (EWuD) algorithm which aims at meeting upstream frame delay requirement while reducing ONUs' energy consumption as much as possible. The role of EWuD algorithm is to select an appropriate time for triggering EWF taking into consideration two factors: (1) buffer overflow probability and (2) delay requirement violation of upstream frames. We evaluate EWuD performances using our TDM-PON OPNET Modular based simulation model under wide range of scenarios. Findings demonstrate that our proposed EWuD can successfully meet delay requirement of all upstream frames while reducing ONU's energy consumption significantly. Moreover, energy saving approaches comes with different types of grants that the OLT can assign to an ONU (i.e. upstream, listening and gratuitous grants). We introduced a solution aim at managing different types grants an make sleeping ONUs intelligent by comprehending the time of receiving a gratuitous grants in order to increase their energy saving.