Library /sys$common/syshlp/ncphelp.hlb SET, MODULE, X25-PROTOCOL, KNOWN_DTES, INTERRUPT TIMER seconds  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 This is the interrupt timer (ISO T26 timer). This parameter can
 only  be used with the ISO8208 profile. Specify a value in the
 range 1 to  255. If you do not specify a value there is no time
 limit on interrupt  acknowledgments.