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

    Default: 512           Value: 0-65535

    Size, in octets, of each receive buffer for the link. You can
    modify this characteristic only when the entity is disabled.
    Also, you can only increase the characteristic value.