Library /sys$common/syshlp/nclhelp.hlb set, llc2, sap, link, maximum_data_size  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: 1027          Value: 1-65531

    Specifies the largest frame size, in octets, the link can use to
    send or receive data. This value does not include the size of the
    frame header.