1. A communications network device comprising: a sampler, wherein the sampler is configured to produce a sampled signal characteristic by virtue of being configured to sample a signal characteristic; a comparator, wherein the comparator is configured to compare the sampled signal characteristic and a record characteristic, and the record characteristic is stored in a table of record characteristics; and a controller, wherein the controller is configured to increase an activity value, if the comparator indicates that the sampled characteristic and the record characteristic match, and decrease the activity value, if the comparator indicates that the sampled characteristic and the record characteristic do not match, and the activity value corresponds to the record characteristic.