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

    Default: 1500          Value: 262-65532

    Maximum number of bytes that users of the data link can specify.
    This number applies to both transmit and receive frames.

    The value of this characteristic must be greater than or equal to
    the value of the minimum data size characteristic. You can modify
    this characteristic only when the entity is disabled.