363-206-285
Maintenance Description
Issue 3 June 2001
9-25
the protection OLIUs are the protection fibers. Fibers and OLIUs shown in bold
are active and carrying service.
In Figure 9-12(a), transmitted optical signals in each direction are permanently
bridged to the service and protection fibers. The same signal is transmitted on
both fibers. Each service and protection fiber and its associated OLIU are
monitored as a set. The fiber/OLIU set selected by the receiving location is the
active set and the ACTIVE LED, which in this figure is on the service OLIU circuit
packs, is lit. The fiber/OLIU set not selected is the standby set, and the ACTIVE
LED on its corresponding OLIU is not lit.
Contrary to other transmission circuit packs, ACTIVE LEDs on both OLIUs may be
litatthesametimeonthesameshelf.Forexample,inFigure9-12(b)thereceive
fiber going to location C has been cut. Location C selects the protection fiber/
OLIU set as active, resulting in the lighting of ACTIVE LEDs on both the OLIUs at
location C. Location A did not switch to its protection set but continues to remain
on the service set. This example illustrates the SONET standard of unidirectional
APS. Since each location sends APS information to the other end, both ACTIVE
LEDs on the OLIUs at location A are also lit.
After the cut service fiber is repaired, location C does not switch back (revert) and
select the service set as its active fiber/OLIU set. This example, Figure 9-12(c),
illustrates the SONET standard of nonrevertive APS.
Figure 9-12(d) and Figure 9-12(e) illustrate a second fiber failure and the resulting
changes to the active OLIUs thus showing that both protection sets could be
active and carrying service.
APSInitiationCriteria 9
The APS is initiated by signal fail and signal degrade conditions on the received
optical signal. The BER of the received optical signal is calculated from violations
in the SONET line overhead B2 parity bytes. Signal fail is declared for:
— OC-3 incoming LOS
— OC-3 LOF
— OC-3 line AIS
— OC-3 line BER exceeding 10
-3
.
An OC-3 line BER exceeding a provisionable 10
-5
to 10
-9
threshold causes the
signal degrade condition. An APS is completed within 60 milliseconds of the
beginning of a hard failure such as a fiber cut. The DDM-2000 OC-3 Multiplexer
APS is "span independent." In multispan applications an automatic or manual
protection switch on one span does not cause a protection switch on any other
span.
To Next Page
Loading...
Need help?
General
