Library /sys$common/syshlp/ncphelp.hlb SET, CIRCUIT, DYING THRESHOLD number  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies to DDCMP CONTROL circuits.  It specifies the number of
 times to poll the active or inactive tributary before changing
 that tributary's polling state to DYING because of receive
 timeouts.  Number must be a decimal integer in the range 0  to
 255. The default number is 2.