Sizing Buffers of IoT Edge Routers

In typical IoT systems, sensors and actuators are connected to small embedded computers, called IoT devices, and the IoT devices are connected to one or more appropriate cloud services over the internet through an edge access router. A very important design aspect of an IoT edge router is the size of the output packet buffer of its interface that connects to the access link. Selecting an appropriate size for this buffer is crucial because it directly impacts two key performance metrics: 1) access link utilization and 2) latency. In this paper, we calculate the size of the output buffer that ensures that the access link stays highly utilized and at the same time, significantly lowers the average latency experienced by the packets. To calculate this buffer size, we theoretically model the average TCP congestion window size of all IoT devices while eliminating three key assumptions of prior art that do not hold true for IoT TCP traffic, as we will demonstrate through a measurement study. We show that for IoT traffic, buffer size calculated by our method results in 50% lower queuing delay compared to the state of the art schemes while achieving similar access link utilization and loss-rate.