NISCS_PORT_SERV provides flag bits for PEDRIVER port services:

    o  Setting bits 0 and 1 (hex bitmask value 3) enables data
       checking.

    o  Setting bit 2 (hex bitmask value 4) enables data compression
       on all virtual channels (VCs) to nodes that support
       compression.

    The remaining bits are reserved for future use.

    Starting with OpenVMS Version 7.3-1, you can use the SCACP
    command SET VC/CHECKSUMMING to specify data checking on the VCs
    to certain nodes. You can do this on a running system. (For more
    information, see the SCACP documentation in the VSI OpenVMS System
    Management Utilities Reference Manual.

    Starting with OpenVMS Version 8.3, you can also use the SCACP
    command SET VC/COMPRESSION to specify data compression on the
    on the VCs to certain nodes. You can use SCACP to enable either
    data checking or data compression on a running system. (See the
    SCACP documentation in the the VSI OpenVMS System Management
    Utilities Reference Manual for more information. Also starting
    with OpenVMS Version 8.3, the NISCS_PORT_SERV system parameter
    is dynamic, that is, changing the setting of this parameter no
    longer requires a reboot. Furthermore, this parameter applies
    to all virtual circuits between the node on which it is set and
    other nodes in the cluster.

    NISCS_PORT_SERV has the DYNAMIC and AUTOGEN attributes.