5-10
SYNCHRONIZATION OF DIGITAL FACILITIES
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Loss of signal (LOS) at the (SCS) circuit for more than 200 ms. A switch is made to the high-
accuracy clock (HAC) on the SCS by the SCS. A further analysis is then made to determine if
the LOS is network related or switch related. A switch to a healthy reference is done if
appropriate.
Blue alarm means that the switch cannot be used as a reference.
Out-of-lock (OOL) condition means that the HAC is unable to lock onto the incoming clock
from the current DS1 reference. A switch to a healthy reference is done if one is available.
Otherwise, a switch to the HAC is performed.
Red alarm means that two out of four (or worse) framing patterns were received.
Slip rate of selected DS1 facilities (with respect to the primary reference) exceeds a given
threshold
Misframes at the primary reference exceed a given threshold
Reception of a yellow alarm (or a blue alarm for R2V4, 1.1 and later)
Health of SCS circuit pack
Insane condition of the board processor on a DS1 circuit
Table 5-1, SCS References Switches, summarizes these conditions:
TABLE 5-1. SCS References Switches
Primary Secondary Reference Indicators
Reference
Indicators RED BLUE YEL GOOD LOS MISF BO
RED HACHACSEC SEC HACSEC HAC
BLUE HAC HACSEC SEC HACSEC HAC
YEL PRI PRI PRI SEC PRIPRI PRI
GOOD PRIPRIPRIPRI PRIPRI PRI
LOS HAC HACSEC SEC HACSEC HAC
MISF PRI PRI SEC SEC PRI PRI PRI
BO HACHAC SEC SEC HAC SEC HAC
BLUE
RED
YEL
LOS
HAC
BO
MISF
GOOD
Blue alarm
Red alarm
Yellow alarm
Loss of signal
System 85's internal high-accuracy clock
Maintenance busied out
Misframe
No alarms
The SCS circuit pack's health is examined when the system clock's health is evaluated. Error
conditions of varying severity can exist on the SCS. If the fault is minor and the SCS can still lock on
the current DS1 reference, a low-priority request for a soft switch to the offline side is made after an
unsuccessful attempt to clear up the error condition on the SCS. If the SCS cannot lock onto the
current DS1 reference clock, a high-priority request for a soft switch is made. The offline SCS is also