Library /sys$common/syshlp/ncphelp.hlb SET, LINE, HOLDBACK TIMER milliseconds  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies only to X.25 lines.  Specifies the maximum delay before this
 X.25 software acknowledges successful receipt of data.  If you do not
 specify this parameter, then the acknowledgment is sent immediately.
 If you specify a holdback timer, performance may be improved by
 allowing the acknowledgment to be included with a subsequent data
 message transmitted.  This parameter cannot be set to a value larger
 than one half the value of the RETRANSMIT TIMER parameter.