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Ask the Wizard Questions

UCX: Telnet questions

The Question is:

Telnet sessions from HP workstations or  PC's using KEATERM.

VMS 6.1 does not drop the telnet session if abruptly logged
off, such as a power failure or PC reboot. The user can log
in again but he has two sessions active although only one is
valid.  I would think vms would be able to determine an inactive
session and terminate. This is causing a frequent trouble
of user limit exceeded. I cannot increase the user limit due
to system resources. The proper fix would be for VMS to idendify
that the lost TELNET session  and kill that process. Any ideas??

The Answer is:

      The behaviour you describe is a feature of IP protocol. One of the
    reasons IP is often claimed to be "more efficient" than DECnet is that,
    unlike DECnet, IP does not "monitor" the link, periodically checking
    that both ends are still alive.  If an application attempts to use the
    link, after it's broken, it will receive an error. It's then up to the
    application to do somethine about it. However if there are no requests
    made, the application doesn't know the link has gone. In your case, an
    I/O has been posted, but it won't time out. This is both an advantage and
    a disadvantage. For example, you may be able to break a link (say hang up
    a  modem), then later reestablish it, without the "participants" knowing.

      The disadvantage is that all applications which use the network must
    implement their own timeout/retry/abort/whatever algorithms or you can
    end up with processes which hang around unaware that their network
    partner has gone away. TELNET is an example of an application which
    doesn't perform such checks.

      However, all is not lost if you are using UCX for TCP/IP. You can
    configure your TELNET sessions to use virtual terminals with the


    The effect is that your physical TNAxx terminals will be placed
    "behind" a VTAxx device. OpenVMS will detect any disconnections. The
    TNAxxx process will be deleted after (SYSGEN) TTY_TIMEOUT seconds
    unless the user logs in again, in which case they will be given the
    option to reconnect to their existing session and pick up where they
    left off (very handy if your PC crashes or modem drops in the middle of
    a 2 hour edit session!).

      The default TTY_TIMEOUT is 15 minutes. You can adjust it up or down
    dynamically according to your needs.