The LAPB module implements one of the protocols in the Link layer
    described by the Digital Network Architecture.

                                NOTE

    For Tru64 UNIX, the WAN Device Drivers are provided as an
    installable subset within the product HP Wide Area Network Support
    for Tru64 UNIX.  You must install this subset before you can refer
    to LAPB module entities in an NCL command.

    For OpenVMS, you must install the WAN Device Drivers from the
    HP X.25 for OpenVMS product before you can refer to the LAPB
    module entities in an NCL command.