User`s manual

Local Loopback (LL)
Data received from the network passes through the line receiver and loops back through the line driver to the network. The
LL is bilateral. Data from the DTE passes through the the transmit logic (Tx) and the receive logic (Rx) back to the DTE.
Figure 10, LL (Local Loopback)
Remote Terminal (RT)
Data from the network passes through the interface, the transmit and receive logic, back to the network.
Figure 11, RT (Remote Terminal)