LOS | The Loss of Sync LED lights when the unit |
| loses synchronization with the incoming sig- |
| nal. This may happen when there is a fram- |
| ing mismatch or a loss of signal. In |
| unframed mode, the LOS LED monitors the |
| status of the transmit clock. |
ALM | The alarm LED indicates the presence of a |
| AIS or RAI, or Out of Frame condition. The |
| ALM LED will blink on every |
| Alarms may occur due to: |
| • Loss of Synchronization |
| • Loss of Frame |
| • AIS (Blue Alarm) |
| • RAI (Yellow Alarm) |
ERR | The error LED indicates various error condi- |
| tions, including framing bit errors, excessive |
| zeros, controlled slips, severe errors, or bit |
| errors (when sending V.52 test patterns). |
| When sending a test pattern, the LED will |
| remain lit if the unit does not receive the |
| identical pattern. When it receives the cor- |
| rect pattern, the LED will turn off. If error |
| insertion is on, the LED will blink once a |
| second if everything is operating properly. |
TST | The test indicator LED blinks with a specific |
| pattern depending on the type of test mode. |
| When the unit is in local analog loop, the |
| LED will blink on briefly. When the unit is in |
| remote loop, the TST LED will blink off |
| briefly. When the unit is sending a test pat- |
| tern or is putting the remote unit into V.54 |
| loopback, the TST LED will stay on. These |
| are the test modes: |
| • V.54 Loopback & V.52 Patterns |
PWR | The power indicator LED will remain lit while |
| the unit is powered. It turns off when the |
| unit is not powered. |
5.2 LOOP (V.54 & TELCO) DIAGNOSTICS
The Model 2715 offers three V.54 loop diagnostics. Use these diagnostics to test the NTU and any communication links. These tests can be activated via the software control port (See Section 3.2.3 System Diagnostics) or via signals on the serial port interface.
5.2.1 Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local Model 2715, and is performed separately on each unit. Any data sent to the local Model 2715 in this test mode will be echoed (returned) back to the user device (i.e., characters typed on the keyboard of a ter- minal will appear on the terminal screen).
To perform a LL test, follow these steps:
1.Activate LL. This may be done in one of two ways:
a. Enter a Local Loop from the System Diagnostics/Statistics menu and toggle the <Spacebar> until “LL” appears next to the a Local Loop option.
b.Activate the “LL” signal on the DTE. If you are not sure which lead is the “LL” signal, please refer to Appendix D.
2.Verify that the data terminal equipment is operating properly and can be used for a test.
3.Perform a V.52 BER (bit error rate) test as described in Section 5.3.3. If the BER test equipment indicates no faults, but the data terminal indicates a fault, follow the manufactur- er’s checkout procedures for the data terminal. Also, check the interface cable between the terminal and the Model 2715.
5.2.2Operating Remote Digital Loopback (RDL)
The Remote Digital Loopback (RDL) test checks the performance of both the local and remote Model 2715, as well as the communica- tion link between them. Any characters sent to the remote Model 2715 in this test mode will be returned back to the originating device (i.e, characters typed on the keyboard of the local terminal will appear on the local terminal screen after having been passed to the remote Model 2715 and looped back).
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