2-18
UAS 7001 NIU
GDC 087R706-000-02
Declared Alarms
Loss of Signal (LOS) – occurs when the unit senses the absence of T1 signal. Absence of
signal for a time equivalent to 175 bits (± 75) is considered no signal.
Loss of Framing (LOF) – occurs when the NIU misses two out of four T1 framing bits
Alarm Indication Signal – reported when the unit receives an AIS at its T1 interface
Received Yellow – reported when the unit receives a Yellow alarm at its T1 interface
Timing Loss – occurs when the unit loses timing from its configured primary Transmit
Clock Source
Performance Alarms
Bipolar Violations – a Bipolar Violation occurs when the signal the unit receives at its T1
interface does not alternate between signal levels as required for Alternate Mark Inversion
(AMI) or Bipolar with 8 Zero Substitution (B8ZS) data encoding; the alarm occurs when
Bipolar Violations exceed the configured interval and threshold limits
CRC Errors – a CRC Error occurs when ESF framing is in use and the CRC-6 code, which
the unit calculates on each 24-frame block it receives, does not match the CRC-6 code
calculated by the unit that transmitted the signal; the alarm occurs when CRC Errors exceed
the configured interval and threshold limits
Errored Seconds – an Errored Second contains at least one CRC error or Out of Frame
(OOF) event; the alarm occurs when Errored Seconds exceed the configured interval and
threshold limits
Bursty Errored Seconds – a Bursty Errored Second contains between 1 and 320 CRC
errors; the alarm occurs when Bursty Errored Seconds exceed the configured interval and
threshold limits
Severely Errored Seconds – a Severely Errored Second contains more than 320 CRC
errors or an OOF event; the alarm occurs when Severely Errored Seconds exceed the
configured interval and threshold limits
Unavailable Seconds – an Unavailable Second is one that contains at least 10 consecutive
Severely Errored Seconds; the alarm occurs when Unavailable Seconds exceed the
configured interval and threshold limits
