Causes a Physical layer to place the line in loopback mode

    startloop [node node-id] modem connect line line-name -
              mode mode-type

    The Mode argument is required.  It specifies the type of loopback
    used on the line.  The possible mode-types are:

    connector        Data is looped through a loopback connector
                     attached to the communications device.

    device           Data is looped in the communications device.

    driver           Data is looped in the driver of the
                     communications device.

    external         Data is looped through a null modem or a modem in
                     loopback mode.

    local            The communications device switches its local
                     modem into loopback mode by asserting the local
                     loopback signal. Data is then looped through that
                     modem.

    remote           The communications device switches the remote
                     modem into loopback mode by asserting the remote
                     loopback signal. Data is then looped through that
                     modem.

1  –  Exception Messages

 o  already in loopback

    The modem connect line entity specified in the command is already
    in loopback mode. Check that you specified the correct entity.
    Reissue the command with the correct name.

 o  line not connected

    You have specified the value remote for the mode argument, yet the
    line is not connected. Connect the line (using the dial command)
    and the reissue the startloop command.

 o  line disabled

    The line entity must be enabled before loopback.

 o  constraint violation

    A startloop mode constraint has been violated.