Energy-saving Protocol For Hybrid Optical-Wireless Broadband Access Networks (HOWBAN)

Fusing the advantages of the optical access technology and the wireless technology, the Hybrid Optical Wireless Broadband Access Network (HOWBAN) can provide users with flexible, convenient and highly cost-effective broadband access service, and is the inevitable trend of access network. The traffic of the access networks presents volatility in day. When the network load is low, some of the nerwork’s equipments are idle and wasting much energy. Besides, the back-end of HOWBAN—EPON asks that each ONU has to monitor and detect the downward data. This also wastes energy. However, in today’s society, energy is shortage and saving energy is very important. Therefore, how to design a reasonable energy-saving mechanism is a critical problem to be solved in HOWBAN.In this paper, the basic concept and the development trend of HOWBAN are firstly introduced. Based on these, it deeply analyzes the existing energy-saving mechanisms in EPON which is the back-end of HOWBAN, and focuses on discussing a Downstream Centric Scheduling (DCS) algorithm which is based on the dynamic bandwidth allocation algorithm of EPON. In the DCS algorithm, when it’s not time to transfer the upstream data but ONU has to receive downstream data, it directly switches ONU into operation mode from sleep mode. However, equipments that complete the uplink transmission are idle and wasting energy. On the other hand, DCS algorithm doesn’t indicate who controls ONU’s sleep. So according to these deficiencies of DCS algorithm, an improved DCS energy-saving algorithm is proposed. It controls the transmitter of ONU opened and closed based on the beginning and end of the uplink time. When the transmitter of ONU is closed, it controls the receiver of ONU opened and closed based on whether there is downward data to receive. The improved algorithm tries to make free equipments in ONU into sleep mode to reduce the network energy consumption. The simulation results show that the improved algorithm can save more energy and also ensure the quality of network service.Then, based on analyzing the existing routing protocols in HOWBAN, and direct at the shortage that these routing protocols just consider the wireless delay, but ignore that ONU’load has important implications for group delay in EPON, a risk-aware energy-efficiency routing protocol considering the whole network’s delay is proposed, which is also based on the improved DCS energy-saving algorithm. It not only considers the front of hybrid network—wireless network’s delay, but also the back-end of hybrid network—EPON’s delay. The simulation results show that the improved algorithm can improve network’s throughput and reduce the network group delay.