The RT-TCP/IP Filter driver is an extensible interface between the RT-TCP/IP Protocol Stack and the network interface card (NIC) driver. This interface is modified to provide the user the ability to filter all packets at the MAC layer and to send MAC packets directly to the NIC driver. This figure provides an overview of where the filter driver fits into the overall architecture.
RT-TCP/IP Architecture with Filter
The RT-TCP/IP Filter driver is based on RT-TCP/IP's proprietary driver interface, which is broken down into two function sets: the Real Time Network (RTN) functions and the Real Time Network Device (RTND) functions.
The RTN functions are functions provided by the RT-TCP/IP Protocol Stack for use by RT-TCP/IP Filter Drivers. These include functions for allocating frames and passing frames up to the RT-TCP/IP Stack.
The RTND functions are those functions that must be exported by the RT-TCP/IP Filter Driver itself for use by the RT-TCP/IP Protocol Stack. These functions are used to send a packet out to the filter.
RT-TCP/IP Filter drivers are written as RTDLLs that are explicitly linked with the RT-TCP/IP Protocol Stack on an as-needed basis. The RT-TCP/IP Stack uses the information set through the control panel to determine which RTDLL to load.
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