User guide

42 DC 900-1303C
Freeway Client-Server Interface Control Document
2.3.4 Protocol Header Format
The Protocol header immediately follows the ICP header for all packets that are for-
warded to the ICP.
The Protocol header is 16 bytes and must remain in the byte order of the machine on
which the header is produced. The use of the Protocol header is protocol-specific. For a
detailed description of each field, refer to the programmer’s guide for the appropriate
protocol. The
DLI_OPT_ARGS structure is defined in the Freeway Data Link Interface Ref-
erence Guide and is used for specifying packet contents when using the “raw” mode of
DLI.
The fields in the Protocol header are as follows:
Command (2 bytes)
This field is equivalent to the
usProtCommand field in the DLI_OPT_ARGS structure.
Modifier (2 bytes)
This field is equivalent to the
usProtModifier field in the DLI_OPT_ARGS structure.
Link ID (2 bytes)
This field is equivalent to the
usProtLinkID field in the DLI_OPT_ARGS structure.
Protocol Header
Command 2 bytes
Modifier 2 bytes
Link ID 2 bytes
Circuit ID 2 bytes
Session ID 2 bytes
Sequence Number 2 bytes
Reserved 1 2 bytes
Reserved 2 2 bytes