25 26The Model 2720 receiving a RL can be in one of the following states:RxPr The Model 2720 is receiving a preparatory pattern.Sack The Model 2720, upon receiving a preparatory pattern,sends an acknowledgement message.RL The Model 2720 is in remote loopback mode.RxTr The Model 2720 is receiving a terminate loopback mes-sage.Wt1s The Model 2720 is waiting for a sequence of all ones andwill time out if it does not receive it.IdleP The Model 2720 is sending a QRSS, 511 or 2047 pattern.Off The Model 2720 is in local loopback.Test Pattern Idle(default)Options: Idle or SendingTo send a pattern, press the ‘c’ key and press to sendthe test pattern. The “OK” message indicates the received test patternis error-free. The “BE” message indicates errors in the received pat-tern.Idle Indicates that Model 2720 is not sending a pattern.Sending Indicates that 2720 is sending a pattern.Error Insertion Off(default)Options: On, OffYou may inject intentional errors into the test pattern by turningError Insertion ON. The Error (ERR) LED will blink once per second.Selected Pattern QRRSS (default)Options: QRSS, 511, or 2047Use this option to select the test pattern used to test the link.Note: The front panel test pattern switch will initiate the test patternselected in this menu (default QRSS).Network Interface (NI) STATUSThe Network interface (NI) status is shown inthe middle of the Diagnostics/Statistics screen. The brackets areempty when the link is operating normally. In this example, various twoor three-letter messages are displayed within the brackets, illustratingwhat you may see if the Model 2720 is not connected at all or is in aloss of signal condition. Here are the eight status messages.Excessive zeros [EXZ], i.e., lack of pulses, detected. This conditionmay occur if the unit is not connected to the network, in which case theEXZ is displayed continuously. If EXZ comes on intermittently, theremay be a frame, line code or data rate mismatch between the near andfar-end units.Receiver Carrier Loss [RCL] occurs when 192 consecutive zeroshave been detected at the network interface. RCL clears when a pulseis detected.Frame Bit Error [FE] occurs when there is an error in the framing bitsequence. This may happen due to a disconnected line, mismatchedframing formats or severe errors in the data stream. This error mayindicate a noisy line or cable condition. This error may indicate a noisyline or cable connection if the frames appear to be set correctly.Severe Frame Error [SE] occurs when the framing error exceeds acertain threshold of errors. This may happen due to a disconnectedline, an extremely noisy connection, or mismatched framing.Loss of Sync [LOS] occurs when the T1 framer in the unit cannotsynchronize itself to the received data stream. This may happen due toa disconnected line.Out of Frame [OOF] occurs when no valid frame structure can befound. This may happen due to a disconnected line or mismatchedframing or mismatched framing.Alarm Indication Signal [AIS] indicates that the remote unit or thecentral office is sending a Blue Alarm, because it is not receiving a sig-nal; the alarm is an unframed all-ones signal, mainly used to keep theline alive and to indicate that it is not receiving any signal. This mayindicate that the local unit is receiving a good signal, but that the trans-mit link may be broken.cde
