Installation guide

82 DC 900-1325I
Freeway Server-Resident Application (SRA) Programmer Guide
muxFilterHook function can be called at any time, and any number of times, to begin,
end, or resume filtering of messages.
6.2 SRA Filter Functions
An SRA filter function is declared as follows:
int sraFilter(char *pBuf);
The argument in the call is defined as follows:
pBuf
This is the buffer containing the data to be filtered. The address
is that of a structure referred to as the ICP header.
6.3 Freeway Server Message Buffers
On the Freeway server, data is moved in buffers that are organized as shown in
Figure 6–2. The TSI header, Freeway header, and ICP header (in addition to other infor-
mation) are required for the Freeway server tasks to function properly. The protocol
header and protocol data are available for editing by the SRA filter functions. The
address provided by the message multiplexor (
msgmux) task to the filters points at the
ICP header. The ICP header contains a byte count field that must be modified if the fil-
ters change the number of bytes in the protocol data and header areas. The rest of the
information in the ICP header must not be disturbed by the filters.
The protocol header information depends on the Freeway ICP protocol. For example,
the protocol header information for X.25 is not the same as the protocol header infor-
mation for AWS. It is defined in the programmer’s guide Protogate provides with each
protocol. Please consult the appropriate programmer’s guide for the protocol chosen
for your application.