Dynamic Wavelength And Bandwidth Allocation Algorithms Based On Network Coding In TWDM-PONs

Time and Wavelength Division Multiplexing Passive Optical Networks(TWDM-PON)combine the advantages of Wavelength Division Multiplexing PON(WDM-PON)and Time Division Multiplexing PON(TDM-PON),which has become a more competitive solution for the next generation of PON.In recent years,with the popularity of social network applications and point-to-point(P2P)communication services,the demand for data communication between Optical Network Units(ONU)in PON is constantly increasing,which leads to the bandwidth bottleneck of the access network being more and more serious.Network Coding(NC)technology is introduced into TWDM-PON,which can effectively support P2 P services in access network and improve network resource utilization.However,the application of NC technology to this architecture will bring new influences on its resource scheduling strategies undoubtedly.Therefore,it is necessary to investigate the Network Coding Based Dynamic Wavelength and Bandwidth Allocation(DWBA)algorithms in TWDM-PON.Firstly,we introduce the evolution of PON in this thesis,present the architecture and technical characteristics of TWDM-PON,and investigate the resource scheduling problems of TWDM-PON in details.On this basis,some typical network coding based dynamic bandwidth allocation(NC-DBA)algorithms in TDM-PON are further analyzed,and the research status of NC technology in TWDM-PON are summarized.Secondly,a Network Coding Based Dynamic Wavelength and Bandwidth Allocation(NC-DWBA)algorithm is proposed for TWDM-PON,which supports P2 P services.In this algorithm,by adopting the off-line scheduling mode and with a comprehensive consideration of the Round Trip Time(RTT)of ONUs and the communication requirements of encoding ONU groups,wavelength and bandwidth are reasonably allocated to each ONU.After receiving the Report frames of each ONU,the Optical Line Terminal(OLT)tries to meet the bandwidth requirements of encoded ONUs as much as possible according to the bandwidth requests of each ONU and the current wavelength occupation situation.In order to improve resource utilization,the remaining bandwidth of the non-encoded ONUs is allocated to the encoded ONUs.In addition,considering the delay caused by the introduction of NC for P2 P communication,OLT will adjust the upstream transmission sequence reasonably according to the bandwidth requirement of ONUs,the differences of RTT and the encoding needs when dispatching the ONUs within the encoding group.And meanwhile the principle of the earliest available wavelength is followed to upload the data of the encoding ONU groups with different wavelengths as soon as possible,that can reduce the delay differences between ONUs’ data packets within the encoding group reaching OLT.This algorithm can reduce the queuing delay and end-to-end delay of data packets and improve the network throughput.Then,for TWDM-PON which supports P2 P services,considering different QoS requirements of users,a Network Coding Based Dynamic Wavelength and Bandwidth Allocation with Differentiated Services is proposed(NC-DWBA-DS).The algorithm adopts a hybrid scheduling method and divides each polling cycle into two sub-cycles: online and offline sub-cycle.OLT uses online scheduling to grant uploading time-sensitive Expedited forwarding(EF)service for each ONU in online sub-cycle,while offline scheduling to grant uploading time-sensitive Assured Forwarding(AF)/Best Effort(BE)services in offline sub-cycle,so as to meet users’ different Qo S requirements.The off-line sub-cycle first grants non-encoded ONUs to upload AF/BE services.The use of wavelength gap filling enables AF/BE services of non-encoded ONUs to upload data by the wavelength gaps created by transmitting EF service as much as possible,which is helpful to improve resource utilization.After OLT has allocated the bandwidth of all the AF/BE services of the non-encoded ONUs,the remaining bandwidth of the non-encoded group of light-loaded ONUs will be allocated to the AF/BE services of the encoded ONUs,which is helpful to further improve the network throughput.In addition,OLT sorts the AF/BE services of ONUs according to the ascending order of RTT.By changing the scheduling order of AF/BE services of ONUs and uploading the data of the same encoding ONU group with multiple wavelengths,the queuing delay of AF/BE services in encoding ONU group at OLT could be reduced.The proposed algorithm can reduce the queuing delay and end-to-end delay of data packets and improve the network throughput while guaranteeing the different Qo S requirements of users.Finally,the TWDM-PON network is built based on OPNET simulation software.The two proposed algorithms are simulated and analyzed,and compared with several typical algorithms.The simulation results verify the effectiveness of the proposed algorithms.