Library /sys$common/syshlp/nclhelp.hlb set, x25_protocol, dte, extended_packet_sequencing  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: False         Value: True or false

    Specifies whether the extended packet sequencing facility is
    subscribed to, in which modulo 128 packet numbering is used. If
    false, extended packet sequencing is not used. The profile may
    provide overriding default or legal values.

    Example:

    set x25 protocol dte dte-1 extended packet sequencing false