User guide

9: Client Applications — Commands and Responses
DC 900-1338I 171
9.2.5.1 X21bis Line Status Reports (Optional)
X21bis line status reports are an optional ICP notification of changes in the connection
status of the physical circuits on the link. To enable X21bis line status reports, use the
DLI_ICP_CMD_BIND command message specifying DLI_PROT_SEND_BIND (instead
of 0) in the
usProtXparms[0] field of the DLI_OPT_ARGS. The ICP returns the standard
DLI_ICP_CMD_BIND response message (see Figure 9–9 on page 170), then begins
monitoring the modem signals on the link to determine the connection status of the
physical circuits on the link.
After the ICP detects that the physical link connection can support data transfer, it
reports a
DLI_PROT_RESP_BIND status for the link. If the ICP subsequently detects loss
of the physical link connection, it reports a
DLI_PROT_RESP_UNBIND status for the
link. The ICP reports each such physical line status change by means of a
DLI_ICP_CMD_BIND response message in which the usProtXparms fields of the
DLI_OPT_ARGS contain information. The usProtXparms[0] field contains
DLI_PROT_SEND_BIND to identify the message as an unsolicited X21bis line status
report. The
usProtXparms[1] field reports the new line status as DLI_PROT_RESP_BIND
(online) or DLI_PROT_RESP_UNBIND (offline).