The present invention may be used to estimate operational characteristics of devices that transmit and receive streams of information in a communication system. In one application, the level of occupancy of a FIFO buffer in a processing device such as a router or wireless access point is estimated by monitoring packets transmitted by the processing device. Estimates of the operational characteristics can be used to control communications in the system so that the overall performance is improved. Techniques that can be used to mitigate effects of low signal-to-noise ratio conditions are also disclosed.