Local Area Transport (LAT)

LAT, another DEC proprietary protocol, is optimized for terminal servers for dumb terminals, printers, and modems. As with LAN, it is based on the 48-bit NIC address. TCP/IP is usually available on terminal servers as well, but LAT is more efficient because it can multiplex several terminal messages into a single network message.

LAT was developed specifically for dumb terminal communication (via terminal servers). LAT was designed to be very fast; hence, it will not tolerate WAN delays of any sort. Furthermore, the protocol has no provision to be routed or bridged. Of course, dumb terminals are not a popular item these days, so LAT's popularity has likewise waned.

LAT is managed with the LAT Control Program (LATCP); however, LAT creates and maintains its own network database through "keep alive" messages that it sends out (and receives) periodically; thus, it does not need a domain name server. Examples in Chapter 5 regarding print queues show examples of LATCP commands. The manager edits LAT$SYSTARTUP.COM, and the script SYS$STARTUP:LAT$STARTUP will start up automatically. Instructions for doing this are embedded in the files.

An example of an LATCP display is as follows. This command lists all nodes on the network running LAT.

     $ MCR LATCP     LATCP> show node /all     LAT Control Program    Node Name             Status       Identification    ----------------      -----------  --------------------------------    BEAVER                On            .HS 104 -- OpenVMS V7.1    CSWWW                 Reachable     .HS 104 -- OpenVMS V7.1    EAGLE                 Reachable     OpenVMS/Alpha, Version V7.1    HERON                 Reachable     OpenVMS/Alpha, Version V7.1    LOON                  Reachable     .HS 104 -- OpenVMS V7.1