TM 11-7025-221-10
3-3. Description of Loopback Option.
a. Genera/. The Ioopback option allows incoming group and dedicated user data from earth-side users
to be looped back in the TD-1337(V)/G and returned to the users as incoming data. This option can
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be used as a troubleshooting aid for isolating user-reported problems at the system level. The following
operating conditions are present in the TD-1337(V)/G when the Ioopback option is used.
(1) Inputs from earth-side users are still processed in theTD-1337(V)/G and applied as the supergroup
(SG) output to the modem.
(2) In a TD-1337(V)/G that is operating as a nodal, any one or more of the active demux's can
be placed in Ioopback. The demux's not placed in Ioopback continue to operate in their assigned configurations
as described in (3) below.
(3) In a nodal configuration, the demux's not placed in Ioopback still process the SG inputs from
the modems. Earth-side users associated with these active demux's receive their normal data inputs.
(4) The SG input to each demux placed in Ioopback is not processed. Each demux placed in
Ioopback is automatically configured to receive and process the SG output of the local TD-1337(V)/G.
The demux separates the SG back into the original data group inputs. The data groups are applied back
to the users that are associated with the demux as input data. This configuration allows the user to transmit
and receive back his own data for test and fault isolation purposes.
NOTE
In the following discussions, each memory area is referred to as
the "primary memory" or "alternate memory". The primary memory
is the memory area containing the configuration data being used
for your present operating configuration. The alternate memory is
the other memory area. It is the alternate memory that is used
for Ioopback operation. For example, when the TD-1337(V)/G is
operating in memory 1 mode, memory 1 is the primary memory
and memory 2 is the alternate memory. Memory 2 would be con-
figured for Ioopback option.
b. Activate Loopback Option. Paragraph 3-4 contains procedures to activate the Ioopback option. When
these procedures are performed, configuration data necessary to perform Ioopback are entered in the alternate
memory area. Then a system mode change to the alternate memory is performed and the Ioopback option
is active, A general outline of this procedure is listed in (1) through (4) below.
(1) Local mux configuration data are entered in the alternate memory.
(2) Rmux minimum configuration data are entered in the alternate memory for each active demux
not to be placed in Ioopback.
(3) Loopback option procedures are performed for each active demux to be placed in Ioopback
in the alternate memory.
(4) Operator performs system mode change routine to change mode of operation to use alternate
memory. At this time, the TD-1337(V)/G has the Ioopback option in operation.
back to normal operation. The operator performs a system mode change routine to place the TD-1337(V)/G
back to the primary mode of operation. No further operator actions are required unless alternate configuration
dots must be reentered in the alternate memory.
3-4
