IBM 3708 Description page 75

SDLe
Inactivity Time Out
The 3708 supports the use of an inactivity timeout on its SOLC links. The timeout
is defined in half seconds and can be set to 0 or any number between 60 and 16383.
Zero is the default. If you enter a number between 0 and 60, the 3708 displays an
error message stating that the input is invalid.
The SOLC Inactivity Time Out option is useful in providing host system backup in
environments where constant availability of a host is required. It is often difficult to
determine whether the upstream connection is still active because certain cabling
configurations and modems always present active EIA 232C leads to the 3708 even if
the host is not active. Specifying an SDLC Inactivity Timeout value other than zero
allows the 3708 to detect host failures independent of cabling and modem
configurations.
How the Timer Works
The timer starts when the SOLC link enters an information transfer state, that is,
when a valid SNRM has been received. The length of the timer is half that of the
SOLC Inactivity Time Out value. While it is in an information transfer state, the
3708 checks if any valid frames are received. Frames with errors, such as FCS
errors, are not considered valid frames.
The link is declared inactive if two consecutive timers expire and the 3708 has not
received at least one valid frame. Because the 3708 checks for valid frames only
after a timer expires, it can take a length of time equal to one or one and a half
times the SDLC Inactivity Time Out value before the SOLC link is declared inactive.
When the SDLC link is declared inactive, the 3708 does the following:
• Notifies users that the host connection is lost
• Disconnects all downstream ports connected to the SOLC line that exceeds the
timer
• Generates an error log entry
• Generates and stores an alert AlOi.
When the SDLC link exits the information transfer state, the timer stops.
Whenever the upstream SNA connections are lost because of a malfunction, the
terminal users are notified by a short message. The message consists of the current
3708 10 line followed by the HOST UNAVAILABLE, RETRY LATER message. The port is
then disconnected.
For users operating in protocol conversion mode, the screen is cleared before the
message is displayed.
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IBM 3708
Description