Causes the link subentity to transmit an SMT Echo request
    frame and await the response. If a response is received, it is
    displayed.

    echo  [node node-id] fddi station station-name link link-index -
          target lan-address, data octet-string [,timeout integer]

    The Target and Data arguments are required.  Target is the 48-bit
    LAN address of the target node.  Data is the data to transmit in
    the echo request.  The Timeout argument is optional.  It is the
    timeout in seconds in the range of 1 to 65535.  The default
    timeout is 60 seconds.