Packet filter engine

Abstract

A data processor is connected to a digital communication system such that information packets broadcast on the system are examined to determine if the contents of each packet meet selection criteria, whereupon the packet is coupled to the processor. A state machine or interface processor is connected between the processor and the network, and compares packets to the selection criteria, passing accepted packets and blocking rejected ones. The selection criteria are programmed into the state machine as a decision tree of any length, configuration or data requirements, preferably by the attached data processor, and can include examination of arbitrary sections of the packet for equality/inequality, greater-than/less than, signed and unsigned comparisons and bit mask comparisons. Thus content is variably examined, as opposed to checking for an address or key code at a given byte position. The state machine operates on recognition instructions including byte offset and content specifics. The recognition instructions can include plural distinct criteria, determined by the data processor to serve applications programs running in a multitasking environment. Thus, the data processor compiles a series of recognition instructions that are passed to the state machine as tasks in the multitasking environment are added or deleted, or when a task decides to change selection requirements. Preferably, signaling lines allow the data processor to determine the reason for selection of a packet, for example by the state machine reporting to the data processor its program count upon acceptance.