Bandwidth Allocation and Control Message Scheduling Algorithms for Improving the QoSs of High Priority Traffic in PON

The passive optical network (PON) is the most promising candidate for supporting multiple service classes, i.e., high priority (HP) traffic and best-effort (BE) traffic, in the next-generation broadband access networks. Providing an efficient dynamic bandwidth allocation (DBA) algorithm is the most important issue for supporting multiple service classes of traffic simultaneously. This paper presents a new DBA algorithm, which is the modified version of the hybrid slot-size/rate (HSSR) scheme, and is called the modified HSSR (MHSSR) algorithm. We have also modified the control message scheduling algorithm to fit it to the proposed scheme. In the proposed MHSSR scheme, each cycle time, i.e., the length of a time cycle, is equally divided into two parts. In the 1st part of the cycle time, the bandwidth is dynamically allocated to the HP traffic of all the optical network units (ONUs). In contrast, in the 2nd part of the cycle time, the bandwidth is dynamically allocated to the BE traffic of one or multiple ONUs. Furthermore, to ensure guaranteed service for the HP traffic, the 1 st part of the cycle time is extended while the 2nd part of the cycle time is compressed if the demand of the HP traffic is very high. However, the 1 st part of the cycle time will never be compressed, even at the lightly loaded condition of the HP traffic. The modified control message-scheduling algorithm effectively coordinates the timing sequence between the two parts of the cycle time and ensures the synchronization between two Gate messages to each ONU. We have evaluated the performance of the proposed schemes through numerical simulations in terms of end-to-end packet delay, bandwidth wastage, remaining bytes per time cycle, jitter, and throughput for different offered loads. From the comparative analysis, it can be seen that the proposed scheme provides better performance than the existing HSSR and delay variation-guaranteed schemes.