Stop ftp from closing control connection after 900 seconds?

[Lewis Stiller]

SunOS4.1 and various Ultrix (that I use) has variety of inter-site ftp
characterized by ftp "closes control connection" after about 900
seconds idle time according to the error message. How can I turn this
off?  It is not in either the Ultrix or SunOS man pages that I can
find.

The application is when debugging remotely, but editing locally for
response time reasons, when one wants to retain the ftp connection
after long periods of ftp idleness, say while using rlogin to the
remote site to debug. Now each new file transfer requires a new login
to the remote site.

Thanks--this is the first time I have used this particular posting
program so I hope it works.

lewis
stiller at cs.jhu.edu