Bandwidth Borrowing Technique for Improving QoS of Cluster-Based PON System

Abstract

The usage of online polling-based dynamic bandwidth allocation (DBA) algorithms in a passive optical network (PON) substantially decreases the granting, back-off delays and end-to-end latency when compared to offline polling-based DBA algorithms. One of the major drawbacks of these DBA scheme is lack of fairness in bandwidth allocation for the ONUs connected to a PON system under different load conditions. To improve the quality of services (QoSs) of the PON system cluster-based polling algorithm was introduced. Where the optical line terminal (OLT) separates all active ONUs into several clusters then performs DBA algorithm cluster by cluster in each time cycle and excess bandwidth from one cluster is added as surplus bandwidth to the next cluster once available. But the problem occurs when the initial clusters are exhausted. In this situation, apart from sharing the surplus bandwidth with the next cluster, the initial clusters themselves would need some extra bandwidth to be served. In this paper, cluster-based PON with bandwidth borrowing scheme is introduced to improve the QoSs of the PON system when the initial clusters are highly loaded. Where the OLT separates all active ONUs into several clusters throughout each time cycle, but here apart from sharing the surplus bandwidth, the highly loaded initial clusters will borrow bandwidth from the next cluster, and continue it up to the last cluster in each time cycle to fit the boundary of a time cycle. For this scheme, performances are evaluated through simulation for three different performance parameters and the computer simulated results are also compared with the existing cluster-based PON system. The simulation results reveal that the proposed algorithm outperforms the existing one.