User`s guide

206 DC 900-1340I
BSC Programmer’s Guide
A.5 Station Up/Down Reporting
Station up/down reporting is based on line activity (as opposed to DSR/DCD up/down
reporting, Section A.6, which is based on modem signals). When a link is started, all sta-
tions are assumed down. As stations become active, the BSC 3270 software notifies the
client with the
DLI_PROT_RESP_ERROR error report containing the DLI_ICP_ERR_STATION_UP
information code. When a station down condition is detected, BSC 3270 notifies the cli-
ent with the
DLI_PROT_RESP_ERROR error report containing the DLI_ICP_ERR_STATION_DOWN
error code. Station up/down messages are generated when there is a change in station
status or as a response to a Specific Poll command.
A link configured as a control station considers a remote tributary station (control unit)
to be up when it receives a response to a poll or select sequence. It considers a station
down when the station fails to respond to a general poll sequence within the specified
timeout and retry limits.
A link configured as a tributary station reports its connection to the control station as
an up/down indication. A tributary considers itself up when a poll or select sequence
with the proper control unit number is received. The tributary considers itself down
when a valid poll or select sequence is not received within the time period specified by
the interpoll delay option (Section 4.21 on page 101).
A.6 DSR/DCD Up/Down Reporting
If the data set ready (DSR) or the data carrier detect (DCD) modem signal (depending
on the setting of the modem control option, Section 4.14 on page 95) is lost while a link
is active, BSC 3270 suspends line operations for that link and notifies the client with the
DLI_PROT_RESP_ERROR error report containing the DLI_ICP_ERR_DSR_DOWN error code. At
that time, all ICP message buffers that are queued for transmission are discarded. The
client receives the
DLI_PROT_RESP_LOCAL_ACK data acknowledge with the
DLI_ICP_ERR_DSR_DOWN error code for each discarded message buffer.