The impact of master–slave bridge access mode on the performance of multi-cluster 802.15.4 network

Individual IEEE 802.15.4 clusters with separate coordinators can be interconnected to form larger networks. In this paper, we investigate the performance of 802.15.4 beacon enabled network which consists of κ source clusters interconnected to a sink cluster in a master–slave manner. The bridging function is performed by the coordinator of the source cluster, which periodically visits the sink cluster as an ordinary node. The bridge can deliver its data to the sink coordinator either by competing with other nodes in the sink cluster using the CSMA-CA access mechanism, or by using the dedicated GTS slots allocated by the sink coordinator. We compare the performance of these approaches under varying cluster size and packet arrival rate, and also consider both acknowledged and non-acknowledged transmission in the CSMA part of the superframe. We have presented numerical and simulation results for κ = 1 and κ = 2 and discussed the performance trend when κ further increases. The results for single source cluster show that under variable and low to moderate network loads, the CSMA approach is more adaptable to traffic conditions than GTS; under moderate to high loads, the use of acknowledged traffic leads to drastic performance deterioration of the CSMA bridge, whereas the GTS bridge is still able to provide reasonable performance. When number of source clusters increases, acknowledged CSMA-CA bridge mode shows larger performance deterioration in the inter-cluster traffic than in the local sink traffic. GTS interconnection in the presence of multiple source clusters, preserves the intensity of inter-cluster interconnections but it sacrifices the performance of the local sink traffic. In non-acknowledged mode with multiple source clusters, CSMA-CA interconnection performed in a more balanced way than GTS one, by deteriorating inter-cluster traffic and local traffic almost equally. The use of non-acknowledged transfer is preferred in all cases where the requirements of the sensing application allow it.