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8-10
MAINTENANCE AND ALARMS
Blue Alarm
The blue alarm shows that maintenance activities are in progress and that the out-of-service condition
exists for that DS1 facility. This alarm is recognized as a continuous stream of 1s with no provisions
for framing. Depending on the particular NCTE being used, this alarm condition may be treated
differently. This condition may result in the NCTE automatically looping the signal back to the
switch. If the looped facility is providing synchronization, then the synchronization subsystem must
detect that the facility is looped and deal with that condition. Otherwise, synchronization problems
will abound.
Beginning with System 85 R2V4, Generic 1.1, and System 75 R1V5 software, if a blue alarm is
received from the primary synchronization reference facility, the synchronization software will
automatically switch to the secondary reference.
Major and Minor Alarms
The major and minor alarms are relative error performance indicators for a DS1 transmission facility.
They are calculated based on the number of misframes or CRC errors that occurred over a set
interval. The framing mode that is selected determines whether it is misframes or CRC errors that
are counted, and the length of the interval.
Another important performance indicator that is frequently used for determining how well the
transmission facility is functioning is known as the errored second (ES) count. An ES is simply one
second that contained one or more bit errors in the DS1’s signal. Although the ISDN-PRI does not
provide an ES count directly, table 8-1, MINOR/MAJOR Alarm to Errored Seconds Conversions, can
be used to convert between major and minor alarms and the equivalent number of ESs that were
necessary to cause the alarm.
TABLE 8-1. Minor/Major Alarm to Errored Seconds Conversions
Framing Mode Alarm Type Conversion
Minor
10
≥ ES ≥ 2460 in 41 minutes
D4
Major
ES > 2 per second for 15 seconds
Minor
>1.3 errors per second for 10 minutes
ESF
Major
>320 errors per second for 10 seconds