A Study Of Bandwidth Allocation Algorithms In EPON

With the rapid development of the Internet,demend of a high-speed accesss network is getting higher and higher.EPON,the most popular access network solutions,is deployed massively and worldwidely.As Time Division Multiplexing(TDM)is used in the uplink in EPON to avoid conflict,bandwidth allocation algorithm is a key parameter for system performance.The design of bandwidth allocation algorithm with high channel utilization,low data delay and good energy-saving effect is of great significance to promote the development of EPON technology.At present,the dynamic bandwidth allocation algorithm is widely used by many network operators.IPACT Gated Service and Limited Service have attracted much attention due to their simple scheduling rules and high channel utilization.Although there are many theories to analyze the Gated Service,no perfect mathematic model has been setup to analyse IPACT Limited Service.The difficulty in modeling lies in the restriction on the transmission number in every cycle and the uncertain cycles a packet may be delayed if the cached packet number is large when it arrives.In this paper,from the perspective of an ONU,we consider the Limited Service uplink as an M/G/1 with vacation queue which is gated and limited.The Markov chain is established by selecting the end point of the vacation period(starting point of the work period)and the end point of the busy period as the embedding points.The states transition between embedded points is studied,and the system steady-state equation is established.By solving the steady-state equation,we get the steady-state probability of all embedded point.So we can slove the problem that a packet may be delayed uncertain cycles if the cached packet number is large when it arrives.And a numerical formula for the average delay of data packets is obtained by using concerning knowledge of queuing theory.The accuracy of the theoretical model is verified by simulation.In addition to packet delay and channel utilization,the energy efficiency of the bandwidth allocation algorithm is increasingly becoming an important criterion.However,the IPACT bandwidth allocation algorithm requires the ONU to maintain high power operation during idle periods and under low traffic load.Whether it is for energy-saving or reducing the cost of operators,energy-efficient design and bandwidth allocation algorithm is very important.This paper extends the idea of the Energy Efficient Ethernet standard to achieve energy saving in Ethernet passive optical networks.We proposed an ONU-initiated and terminated sleep scheme.The sleep scheme prevents the ONUs wasting energy on frequent states transitions.If the buffer is empty at the end of upload,the ONU enters the sleep mode.By setting the wake-up threshold or the time threshold,the ONU initiates the wake-up and restores the signaling interaction.Simulation results show that our scheme can save a great deal of energy at the expense of a light increase in packet delay.