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Alarm Definitions
Network and Cascade Alarms
Network/Cascade Out Of Frame
An Out Of Frame (OOF) alarm event occurs when the DSU misses two out of four framing bits in
an incoming T1 signal, a condition that results in loss of synchronization with the signal. A Network
OOF alarm, caused by framing loss at the network interface, also lights the front panel OOF
indicator. A Cascade OOF reflects conditions at the Cascade port. The count for an OOF alarm
increments by one each time framing is lost, regardless of the number of frames affected.
Network/Cascade Loss Of Signal
A Loss of Signal (LOS) alarm event occurs when the DSU senses an absence of incoming signal at
the interface. Absence of signal for a time equivalent to 175 bits (± 75) is considered no signal. A
Network LOS alarm, caused by signal loss at the network interface, also lights the front panel No
Signal (NS) indicator. A Cascade LOS reflects conditions at the Cascade port.
Network/Cascade Alarm Indication Signal
An Alarm Indication Signal (AIS) alarm event occurs when the DSU receives an AIS. A Network
AIS alarm, caused by reception of AIS at the network interface, also lights the front panel AIS
indicator. A Cascade AIS indicates reception of AIS at the Cascade port.
Network/Cascade Unavailable Signal State
An Unavailable Signal State (USS) alarm event occurs when 10 consecutive severely errored sec-
onds occur in the signal being received. It ends when the DSU has processed 10 consecutive sec-
onds of data without the occurrence of a severely errored second. The count for this alarm
increments by one each time the alarm state occurs, regardless of how long it persists. Network USS
reflects conditions at the network interface; Cascade USS reflects conditions at the Cascade port.
Network/Cascade Bipolar Violations
A Bipolar Violation (BPV) alarm event occurs when the T1 signal received by the DSU does not
alternate between signal levels as required for Alternate Mark Inversion (AMI) or Bipolar with 8
Zero Substitution (B8ZS) data encoding. A Network BPV alarm, caused by conditions at the net-
work interface, also lights the front panel BPV indicator. A Cascade BPV reflects conditions at the
Cascade port.
Network/Cascade Cyclic Redundancy Checksum
A Cyclic Redundancy Checksum (CRC) error alarm event occurs when ESF framing is in use and
the CRC-6 code the DSU calculates for the received signal does not match the CRC-6 code cal-
culated by the unit that transmitted the signal. The DSU performs the CRC check on every ESF
frame to detect errors in the T1 signal. Network CRC reflects conditions at the network interface;
Cascade CRC reflects conditions at the Cascade port.
Network/Cascade Received Yellow
A Received Yellow (RYEL) alarm event occurs when the DSU receives a Yellow alarm at its T1
interface. Network RYEL reflects conditions at the network interface; Cascade RYEL reflects
conditions at the Cascade port.
C-2
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Network and Cascade Alarms
076R155-000
Issue 7
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