Library /sys$common/syshlp/nclhelp.hlb set, x25_access, template, calling_address_extension  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: No NSAP address                     Value: NSAP address

    Calling Network Service Access Point (NSAP) address is to be
    passed to a higher-level entity within the called DTE. A null
    address indicates that this facility is not included in the
    outgoing call.