Study On DBA Algorithm For The Coexistence Of Heterogeneous ONUs In Multi-wavelength Optical Access Networks

Passive Optical Network(PON)smoothly evolves in a pay-as-you-grow way.For the past few decades,TDM-PONs have occupied the dominant position of the access network market.TDM-PONs,such as EPON and GPON,are all singlewavelength systems.In TDM-PONs,ONUs have fixed upstream and downstream wavelengths,and the Point-to-Multi Point(P2MP)manner is adopted for the communication connection between OLT and ONUs.With the increasing bandwidth demands of users and services,WDM technology begins to be used in access network.In WDM-PONs,the wavelength number equals to the ONU number,and all ONUs adopt wavelength-tunable transceivers,so that OLT and ONUs can commuicate in the Point-to-Point(P2P)manner.In the process of smooth evolution from TDM-PON to WDM-PON,due to the upgrade on demand,the upgraded and un-upgraded network devices will inevitably exist in the same PON,resulting in different structures of hybrid WDM/TDM-PONs.Hybrid WDM/TDM-PONs are multi-wavelength systems,and its wavelength number is between the wavelength number of TDM-PON and WDM-PON.In WDM/TDMPONs,parts of ONUs are preferentially upgraded by adopting tunable transceivers,expanding tuning ranges,or increasing transceiver numbers,etc.These ONUs with different transmission capacity are defiend as heterogeneous ONU.In other words,with the advance of PON smooth evolution,hybrid WDM/TDM-PON will face with multiple types of coexistence situations of heterogeneous ONUs.The coexistence of heterogeneous ONUs is the essential way of PON evolution.Therefore,the Dynamic Bandwidth Allocation(DBA)algorithms for the full and fair bandwidth allocation among heterogeneous ONUs is the key to support the smooth evolution of PONs.The coexistence scenarios of heterogeneous ONUs are classified as follows: the first type is the coexistence of the ONUs with and without wavelength tunability;the second type is the coexistence of the ONUs with different wavelength tuning ranges;the third type is the coexistence of the ONUs with different numbers of transceivers.The DBA study for the three different coexistence scenarios of heterogeneous ONUs are as follows:1)For the coexistemce scenario of the heterogeneous ONUs with/without wavelength tunability in hybrid WDM/TDM-PONs,a corresponding mathematical model for bandwidth allocation is built.According to the different network bandwidth demands of the heterogeneous ONUs,a differentiated grant sizing algorithm is proposed to acheive the fairness of bandwidth allocation among not only the heterogeneous ONUs but also the heaveliy-loaded and lightly-loaded ONUs.Considering the flexibility difference of the heterogeneous ONUs,a wavelength and time-slot assignment algorithm aiming at load balancing among wavelengths is proposed,the algorithm can greatly shorten the scheduling cycle time and transmission delay level;2)For the coexistence scenario of multi-type users and multi-type services(MUMS)in NG-EPONs composed of multi-transceiver ONUs,a MUMS two-dimensional priority queue is proposed to conduct buffer differentiated management.A novel grant sizing algorithm is proposed to meet the differentiated SLA requirements of multi-type users and the differentiated Qo S requirements of multi-type services.Two grant scheduling algorithms,time-order filling and wavelength-order filling,are proposed and scheduled collaboratively to meet the MUMS's different needs and realize load balancing among wavelengths;3)For the coexistence scenario of the heterogeneous ONUs with different tunning ranges in hybrid WDM/TDM-PONs,a bandwidth allocation model is established.Based on the mathematical model,the ONU aggregation problem is mapped into the knapsack-constrainted multiknapsack problem.Then,a novel ONU aggregation algorithm is proposed.The ONU aggregation algorithm is based on the framework of a branchand-bound sub-algorithm,and adopts a relaxation algorithm and a greedy algorithm respectively as its upper/lower bound approximation subalgorithms.At low loads,the algorithm can greatly reduce the number of occupied wavelengths,and maintain the ONUs' bandwidth satisfaction rate at a higher level.At high loads,the algorithm provides higher network throughput by improving bandwidth utilization per wavelength.