SPARCstation UART, dialup session security

[ruck at beach.cis.ufl.edu]

I've attached a US Robotics Courier 2400 modem to ttyb on a Sun
SPARCstation 1+ running SunOS 4.1.  I am a novice administrator.

We've become concerned about the following security issue: A user will not
be automatically logged out when his telephone call is interrupted.  I've
heard the hypothesis that this problem is unsolvable because it is the
result of hardware limitations of the SPARCstation's UART.  Would someone
please be kind enough to confirm or contradict that explanation?  If there
is an easy solution to my problem, please let me know, and direct me to
the appropriate reference.

Thank you for your responses,

John R Ruckstuhl, Jr
University of Florida		ruck at cis.ufl.edu, uflorida!ruck