Applications
2-14 Issue 8.0 July 2002
!
CAUTION:
The primary node should be connected directly to a node in the other ring.
No intervening transmission equipment (for example, DACS III-2000
Cross-Connect System) should be present. If intervening transmission
equipment is present and a loss-of-signal (LOS) condition occurs, the
intervening equipment may transmit alarm indication signals (AIS) toward
the primary node. In Releases 7.0 and earlier, an incoming AIS will falsely
NOT trigger a DRI protection switch causing service to be dropped. With
Releases 7.1 and later, an AIS will cause a DRI protection switch. The
secondary node can be connected through intervening transmission
equipment to a node in the other ring.
Figure 2-7 shows a DRI application using OC-3 interfaces between a
line-switched ring equipped with FT-2000 OC-48 Add/Drop-Rings Terminals and a
path-switched ring equipped with DDM-2000 OC-3 Multiplexers. There is a direct
intra-office connection between the primary node in the FT-2000 OC-48 two-fiber
ring and Node 2 in the DDM-2000 ring. There is also a direct interoffice
connection, using an OC-3 optical extension, between the secondary node in the
FT-2000 OC-48 two-fiber ring and Node 4 in the DDM-2000 ring.
The DRI application supports synchronous optical network (SONET) path
connectivity between rings with EC-1 and OC-3 interfaces. For example, a DS3
signal may enter a node in a ring, be transported from the primary node to the
other ring as a DS3-based EC-1 signal, then emerge from a node in the other ring
in the original DS3 format. A line-switched ring equipped with FT-2000 OC-48
Add/Drop-Rings Terminals may also accept VT1.5-based EC-1 signals from a
path-switched ring equipped with DDM-2000 Multiplexers. This allows VT1.5 level
cross-connections in the path-switched ring. The OC-3 interfaces may be used
between rings to transport DS3-based and Virtual Terminal (VT)1.5-based EC-1
signals, or STS-3c signals in broadband service applications. DS3 interfaces may
be used between rings; however, DS3 interfaces do not support SONET path
connectivity between rings. DS3 interfaces terminate the SONET path.
A circuit with one termination in the line-switched ring and the other termination in
the other ring (path-switched ring or another line-switched ring) is protected by
two identical input low-speed signals and two identical output low-speed signals.
In the line-switched ring, the primary node and secondary node accept an
identical low-speed signal from the other ring. The primary node selects the
low-speed signal from the other ring as the active low-speed signal and the
low-speed signal from the secondary node as the standby low-speed signal.
The primary and secondary nodes of the line-switched ring also provide two
identical output low-speed signals to the other ring. The primary node bridges the
STS-3 or STS-1 tributary using its drop and continue capability to the secondary
node.
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