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

 Applies only to DDCMP CONTROL circuits.  It defines the number of
 times to poll the active, inactive, or dying tributary before
 changing that tributary's polling state to DEAD because of
 receive timeouts.  Count must be a decimal integer in the range 0
 to 255.  The default count is 8.