395.0 OPERATIONOnce the NetLink-T1™ is installed and configured properly it isready to place into operation. This section describes the function ofthe LED indicators, and the use of the loopback and pattern testmodes.5.1 LED DESCRIPTIONSThe NetLink-T1™ is equipped with nine LED indicators that monitorthe status of communication. Figure 12 shows the location of the LEDs.TXD When the unit sends a one, the TXD LED isgreen. When it sends a zero, the TXD LEDis orange. Moreover, the TXD LED is activeonly in active DS0 channels. In inactivechannels, the TXD LED is off.RXD When the unit receives a one, the RXD LEDis green. When it receives a zero, the RXDLED is orange. Moreover, the RXD LED isactive only in active DS0 channels. In inac-tive channels, the RXD LED is off.LOS The Loss of Sync LED lights when the unitloses synchronization with the incoming sig-nal. This may happen when there is a fram-ing mismatch or a loss of signal. Inunframed mode, the LOS LED monitors thestatus of the transmit clock.ALM The alarm LED indicates the presence of aBlue or Yellow Alarm, or Out of Frame con-dition. The ALM LED will blink on every half-second.40Alarms 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, excessivezeros, controlled slips, severe errors, or biterrors (when sending V.52 test patterns).When sending a test pattern, the LED willremain lit if the unit does not receive theidentical pattern. When it receives the cor-rect pattern, the LED will turn off. If errorinsertion is on, the LED will blink once asecond if everything is operating properly.TST The test indicator LED blinks with a specificpattern depending on the type of test mode.When the unit is in local analog loop, theLED will blink on briefly. When the unit is inremote loop, the TST LED will blink offbriefly. When the unit is sending a test pat-tern or is putting the remote unit intoV.54/CSU loopback, the TST LED will stayon. These are the test modes:• V.54/CSU Loopback & V.52 Patterns• D4 Line Loop (CO initiated)• ESF Line Loop (CO Initiated)• ESF Payload Loop (CO Initiated)PWR The power indicator LED will remain lit whilethe unit is powered. It turns off when theunit is not powered.5.2 LOOP (V.54 & TELCO) DIAGNOSTICSThe NetLink-T1™ offers three V.54 loop diagnostics and is compat-ible with two Telco loop diagnostics. Use these diagnostics to test theCSU/DSU and any communication links. These tests can be activatedvia the software control port (See Section 3.2.3 System Diagnostics),via signals on the serial port interface or the front panel switch.5.2.1 Operating Local Loopback (LL)The Local Loopback (LL) test checks the operation of the localNetLink-T1™, and is performed separately on each unit. Any data sentFigure 12. Model 2710RC front panel, showing LED indicators.Model 2710RC