First off, if the telco DDS circuit is not plugged into the DSU IV then it should be in alarm. If it isn't in alarm with no telco circuit then something is wrong.
The TD LED on the front of the DSU indicates it is detecting a voltage on the transmit pin(s) of the serial connection from the DTE equipment (indicating the end equipment is transmitting data). If TD never comes on then the DSU is not detecting the transmit data from the end equipment.
If you are not getting the data traffic then you should go through the configuration and verify everything is configured properly.
You can use a DDS loopback plug connected to the TELCO port to verify your DTE signal is going through the DSU out the TELCO interface and back again, but your DTE equipment would have to be able to tell the signal was looped and give any reading on the signal that comes back. This would test continuity through the local DSU.
You can run a 2047 test pattern from the DSU to the loopback plug and verify there are no errors detected in the test pattern. This tests the transmit and receive capability of the DDS interface.
Good afternoon Patrick,
Thank you for your quick response.
One question that I have in response is that the TD light is blinking as soon as the telco cable is plugged back in. But the TD does not blink when the telco cable is unplugged.
We are trying to determine where our communication issue is coming from. If it is from the communication between our facilities which is through AT&T or if it is from our DCS.
Both sides are blaming eachother and the modem is in the middle. This one small TD light not blinking on one modem with the telco cable unplugged we are hoping will give us a good direction to persue. Do you have any advice?
Thank you for your time
That really depends on what the DTE equipment requires in order to start transmitting data. If it needs the CD (carrier detect) then that is a signal received from across the DDS circuit, but it can be configured as FORCED ON. If it needs CS (clear to send) you can configure that as follows:
FORCED ON (it will always be on)
FOLLOWS RS (comes on after the DTE equipment raises RS - request to send)
FOLLOWS CD (comes on after CD is detected from the DDS circuit)
FOLLOWS RS+CD (comes on after both RS and CD are detected)
OFF WITH LOCD (turns off 5 seconds after LOCD - switch 56 circuits only)
If the end equipment indicates it is transmitting data, but the DSU doesn't show a TD LED, then either the transmit on the DTE equipment is bad, the cable is bad, or the port on the DSU is bad, or misconfigured. Verify the DSU has the correct DTE CONNECTOR TYPE configured (either EIA 232, or V.35).