Verilink APS 2000 T1 Line Protection (880-502411-001) Product Manual - Manual (Page 76)

Diagnostics
5-12 Verilink APS 2000 User Manual
CSU alarms
The CSU is capable of detecting various equipment and network
trouble conditions, including loss of frame (LOF), and loss of signal
(LOS). It reports each condition as an alarm if the trouble continues
for an operator-specified time interval.
Loss of Signal The CSU goes into a loss-of-signal (LOS) state upon detecting
approximately 175 (
± 75) milliseconds of consecutive ZEROs
(231,600 bits) on the incoming signal from the equipment. The CSU
sends a 511 pattern keep-alive to the network 3 milliseconds later.
Otherwise, it continues to perform network density enforcement.
The signal sent by the CSU to the network upon occurrence of an
equipment-side LOS is selectable by the user.
The CSU clears an LOS alarm upon detecting a period of 10 seconds
(default time interval) in which no LOSs or OOFs occur. The alarm
clearing interval is user-programmable from 0 to 255 seconds.
Out-of-frame and
Loss of Signal
The CSU goes out of frame when the incoming network or
equipment signal is lost, or when it cannot frame up on the
incoming signal. The out-of-frame condition occurs when the CSU
detects errors in any two of four consecutive framing bits.
If the OOF condition persists for two to three seconds, the CSU
enters a loss-of-frame (LOF) state. It reports an LOF alarm after an
additional user-defined delay of 0 to 255 seconds (default = 3
seconds).
Loss-of-frame When the CSU detects LOF on the incoming network signal, it sends
either the LOF alarm-causing signal or a 511 pattern to the
equipment, as configured by the operator. It also passes the DS-1
signal from the equipment to the network.
Figure 0-1
Loss of Frame and Yellow Alarm Processing
CSU CSU
DS-1
EQPT DS-1
EQPT
XMT RCV
RCV XMT
(NETWORK)
LOF detected here
1. CSU passes LOF-
causing signal or
AIS to equipment
2. Equipment sends
Yellow Alarm to CSU
3. CSU sends RAI
to network; also
transcodes to ESF
format if necessary 4. Far-end CSU sends
RAI to equipment;
transcodes to SF if
necessary