Hybrid Flow-Control for CDMA2000

A common ´finite-burst´ mode of wireless links scheduling in CDMA2000 has been shown to cause occupancy oscillations at the bottleneck shared-queue resulting with large overflow-based closely clustered bursts of data-packets drops. The CDMA2000 gateway (PDSN) node is constructed with superior service-rate compared to its downstream core node (PCF). The rate mismatch further allows for traffic load variations and subsequent congestion at the core node. The use of a Xoff/Xon feedback flow control in CDMA2000 was proposed at the 3GPP2. We evaluate the 3GPP2 backpressure proposal for protecting the bottleneck queue during heavy congestion conditions. We devise an adaptive-Xoff/Xon for tandem queues, which extends the traditional Xoff/Xon to provide threshold adaptation according to overflow prediction. The adaptive-Xoff/Xon complements the RED AQM at the bottleneck node, creating a hybrid flow-control model for tandem nodes. Experimental results show that the hybrid flow-control model eliminates packet discards due to overflow at the bottleneck queue, improves throughput, and lowers the overall data packets drop volume. Packets show to not experience backpressure-based delay variation while traversing the tandem queues. An associated cost is low volume of feedback control packets. Larger tandem-queues´ average-delays are observed, which result with lower power-function. Hence, degraded combined performances are delivered by the 3GPP2 proposal for backpressure.