363-206-285
Administration and Provisioning
8-64 Issue 3 June 2001
In Figure 8-8, the DDM-2000 OC-3 shelf at RT3 supports a single-homed OC-1
interface in function unit B. Signals are connected between the OC-3 interface in
main-1 and the OC-1 interface(s) in fn-B-1, and between the OC-3 interface in
main-2 and the OC-1 interface(s) in fn-B-2. Switching is not done on the
DDM-2000 OC-3 Multiplexer on these interfaces; rather VT1.5 level path
switching is done on the DDM-2000 FiberReach Multiplexer and on the DDM-
2000 OC-3 shelf at the CO node. This allows DDM-2000 FiberReach nodes to
interface with DDM-2000 nodes of an OC-3 ring, providing "ring-on-ring"
architecture. Each OC-1 ring so supported occupies up to 28 VT1.5 time slots on
the OC-3 ring. When single-homing is used, the OC-3 system passes the VT1.5
time slots between the OC-1 interfaces and OC-3 interfaces without terminating
them or performing any path protection switching on them. Up to six OC-1 rings
can be supported by one DDM-2000 OC-3 shelf in this way. Since the signals
from the OC-1 ring(s) are sent as two copies (one clockwise, the other counter-
clockwise) on the OC-3 ring, the OC-3 ring capacity is limited to the OC-3 line rate
(84 VT1.5 signals). So, although one DDM-2000 OC-3 shelf can support up to six
OC-1 rings, the full capacity of all six OC-1 rings cannot be carried on the OC-3
ring.
The OC-1 lines between an OC-3 node and an OC-1 node behave like the OC-1
lines between the nodes on an OC-1 ring and do not perform line level protection
switching. Instead, the DDM-2000 FiberReach shelves perform the normal path
protection switching functions.
Some points to note for this application are:
â– Single-homing can be thought of as a "ring on ring" with many of the
characteristics of a single ring.
â– Pass-through cross-connections may be required at the VT level on both
theOC-1andOC-3rings.
â– The OC-1 ring can be composed of up to 28 VT1.5 signals from the OC-3
ring.
â– More DDM-2000 FiberReach wideband shelves could be added to the
OC-1 ring. A cross-connection from the OC-1 interface to a DS1 interface
would be required at one of the DDM-2000 FiberReach wideband shelves
on the OC-1 ring, and pass-through cross-connections would be required
at all other DDM-2000 FiberReach wideband shelves on the OC-1 ring.
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