1. In a system for monitoring and controlling a data communications network which communicates a serial stream of binary bits having a characteristic pattern, comprising: a base Event Driven Interface having an input coupled to said data communications network, programmed to process the serial stream and identify event bit patterns in said serial bit stream whose occurrence is an event to be counted, for outputting an event signal in response to identifying and selecting an event bit pattern; an extension Event Driven Interface having an input coupled to said data communications network, programmed to process the serial data stream simultaneously and in parallel with the event driven interface to identify category bit patterns in said serial bit stream, which are significant bit patterns for one of a plurality of categories of data frames in said serial bit stream, for outputting a selection signal in response to identifying a one category bit pattern; a plurality of event vector counters in levels, each level corresponding to a respective one of said plurality of categories, each counter thereof having an event input selectively coupled to said output of said base Event Driven Interface, for receiving said event signal, and each counter having a selection input coupled to said output of said extension Event Driven Interface, for enabling the counter to receive said event signal in response to said selection signal.