Research On The Dynamic Bandwidth Allocation Algorithm Of EPON System

In recent years, optical access network is gradually becoming a mainstream technology in access network field. Ethernet passive optical network (EPON) has become the most promising solution due to its characteristics of fast speed, low cost, low overhead and flexible network structure. The sharing of uplink bandwidth is one of the most research emphases of EPON system, and the key technology of resolving this problem is dynamic bandwidth allocation algorithm. An effective dynamic bandwidth allocation algorithm can guarantee the fairness among all ONUs, improve bandwidth utilization ratio, and reduce delay of every kind of services, as well as improve system throughput. Thus, dynamic bandwidth allocation algorithm plays an important role in performances and efficiency of EPON system.In this paper, some important technologies of EPON system, including topological structure, principles of uplink and downlink data transmission, ranging, MPCP and DBA, was researched in depth. In addition, two kinds of classical dynamic bandwidth allocation algorithms was introduced, so as to some new algorithms proposed recent years. The merits and demerits of these algorithms were analyzed subsequently. On this basis, a novel algorithm, which adapts two-stage scheduling mechanism, was proposed. Based on the fairness of all ONUs, the scheme of authorization in advance was introduced in OLT, which improved the bandwidth utilization ratio to a certain extent. Moreover, ONU adapted the preempted storage mechanism based on limited cycle, and sent data according to the strict priority in uplink direction. This preempted storage mechanism was able to guarantee the delay of high priority service and avoid the low priority packet in the condition of being discarded all the time, thereby reducing delay of low priority service. Thus the performances of EPON system were improved. In the last part, the new algorithm was simulated and analyzed using OPNET simulation software. Meanwhile the performances of new algorithm were compared with the ones of algorithm proposed by J.Zheng. The result proved that the bandwidth utilization rate and time-delay of services of new algorithm put up some degree of superiority.