Library /sys$common/syshlp/nclhelp.hlb loop, loopback_application, length  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The optional argument Length specifies the length, in octets,
    of the data field in each loop message.  The default is 40,
    and the value must be 0-65534.

    loop [node node-id] loopback application name full-name, -
         length integer [,optional arguments...]

    loop [node node-id] loopback application address tower-set, -
         length integer [,optional arguments...]

    Example:

    loop loopback application name DEC:.SCH.LAMCHP, length 80