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Applications
Issue 1 December 1997 2-13
Folded Ring 2
DDM-2000 OC-3 and OC-12 rings offer several benefits in addition to service
assurance. Economically, a ring network minimizes overall network cost by
requiring fewer optical transmit/receive units than a comparable linear add/drop
network. Operationally, a ring network provides significant flexibility to increase
bandwidth at existing nodes and to add new nodes at locations where
unanticipated bandwidth is required.
These benefits make rings highly desirable even when fiber route diversity is not
available. When route diversity is not available on part or all of the ring, ring
technology can be used to support split and tapered feeder routes to derive
economic benefits, provide bandwidth flexibility, ease the process of adding and
deleting nodes and supply survivability against single-node failures.
When route diversity is not available or fiber cable cuts are not a driving concern,
the two-fiber path switched ring feature can be applied in a "folded" (a folded ring
is a single path ring) configuration (Figure 2-7). This use of DDM-2000 OC-3,
OC-12, and
SLC
-2000 access resource manager (ARM) path switched rings
applies in particular to hubbing and linear topologies where there is no return path
from the end remote site to the central office (CO). While a complete cut through
the fiber cable cannot be protected, single-node equipment failures are still
protected. Furthermore, a two-fiber ring ARM uses only one optical transmitter/
receiver in each direction (two per remote shelf), in contrast to a 1+1 line
protection arrangement that requires four optical transmitter/receivers per remote
shelf. Thus the ring configuration reduces equipment costs, a benefit independent
of its survivability advantage. The ring topology also makes node addition/deletion
straightforward.
Figure 2-7. Folded Ring Configuration
OC-3
DDM-Plus
DDM-2000
OC-3
SLC
2000
T1
QUAD
DS1
VF, DS0,
ISDN
DS1
Access
System RT
SLC
2000
MSDT
VF, DS0,
ISDN
DS1
OC-3
RT Site
OC-3
DACS IV 2000
Central Office
DDM-2000
OC-3
OC-3
TO:
5ESS
RT Site
DDM-Plus VF,
DS0
RT
DS1
SLC
2000
Access System
T1
QUAD
DS1
Switch etc.
DS1,
EC-1
R
R
R
R
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