User`s guide

Test Mode Operation
Modem 3600 7-5
Testing the Remote Modem
Use LDL, RDL, and RDL/TP in the online data mode to test the remote
modem and phone line. Enter the escape sequence after making a
connection to return to command mode. The appropriate test command,
&T3, &T6, or &T7, can then be entered to initiate an online test.
Local Digital Loopback &T3
After making the data connection, enter the escape sequence to return to
command mode. Entering &T3 puts the local modem in digital
loopback. The remote operator can now send a test message which is
looped back to the remote terminal screen.
If the test timer (S18) was loaded before issuing the &T3 command the
local modem exits the test after the specified number of seconds and
returns to command mode. If not, enter &T to exit the test. Enter the
command to return to online data mode.
The local modem receiver connects to its transmitter so received data is
retransmitted to the remote site.
If Digital Bilateral Loopback is enabled locally, the local DTE is looped
back to itself (Figure 7-3). If disabled, the local DTE receives a constant
mark.
Figure 7-3. Local Digital Loopback with Bilateral Loopback
Enabled