Issue 1 December 1997 GL-1
Glossary
0x1
See Ring (0x1) Low Speed Interface.
1+1
The 1+1 protection switching architecture protects against failures of the optical transmit/
receive equipment and their connecting fiber facility. One bidirectional interface (two
fibers plus associated OLIUs on each end) is designated "service," and the other is
designated "protection." In each direction, identical signals are transmitted on the service
and protection lines ("dual-fed"). The receiving equipment monitors the incoming service
and protection lines independently, and selects traffic from one line (the "active" line)
based on performance criteria and technician/OS control. In 1+1 both service and
protection lines could be active at the same time (service in one direction—protection in
the other).
1xN, 1x1
1xN protection switching pertains to circuit pack protection that provides a redundant
signal path through the DDM-2000 (it does not cover protection switching of an optical
facility; see "1+1"). In 1xN switching, a group of N service circuit packs share a single
spare protection circuit pack. 1x1 is a special case of 1xN, with N=1. In 1x1 only one is
active at a time.
A
ABN
Abnormal (status condition)
ACO
Alarm Cutoff — A pushbutton switch available on the user panel that can be used to
retire an audible office alarm.
ACO/TST
Alarm Cutoff and Test — The name of a pushbutton on the user panel.
Active
Active identifies a 1+1 protected OC-N line which is currently selected by the receiver at
either end as the payload carrying signal or a 1x1 or 1xn protected circuit pack that is
currently carrying service. (See Standby.)
ADM
Add/Drop Multiplexer.
AIS
Alarm Indication Signal — A code transmitted downstream in a digital network that
shows that an upstream failure has been detected and alarmed.
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