A user equipment (UE) passively determines the presence of a cellular network bottleneck in a downlink channel and may take appropriate actions to mitigate the bottleneck. The UE may analyze the transport block size (TBS) of slots of received downlink traffic and assign states the to various slots based on this analysis. Based on these assigned states, the UE may identify a burst of network traffic from network traffic received from the cellular network, and the UE may also determine the burst duration as well as a busy estimation. The UE may determine that the cellular network is experiencing a bottleneck based at least in part on the burst duration and the busy estimation.