363-206-295
Administration and Provisioning
8-30 Issue 1 December 1997
Single Homed OC-3/OC-12 VT1.5 Path Switched
Ring (0x1) 8
Figure 8-4 shows an example of an OC-3/OC-12 VT1.5 path switched ring (0x1)
single homing application. The figure is placed after the example explanation and
can be removed for reference.
The DDM-2000 OC-12 ring supports ring (0x1) OC-3/IS-3 interfaces in its function
unit slots. These interfaces must be provisioned as ring (0x1). Signals pass
through the DDM-2000 OC-12 transport ring and exit to the DDM-2000 OC-3 ring.
OC-12 function unit slot fn(x)-1 is connected to OC-3 main-1 and OC-12 function
unit slot fn(x)-2 is connected to OC-3 main-2. Switching is not done on the DDM-
2000 OC-12 Multiplexer on these lines, or paths on these lines; rather VT1.5 or
STS-1 level path switching is done on the DDM-2000 OC-3 Multiplexer. This
allows DDM-2000 OC-3 nodes running ring software to interface with DDM-2000
nodes of an OC-12 ring in such a way as to provide ring-on-ring architecture.
Each OC-3 ring so supported occupies up to three STS-1 time slots on the OC-12
ring. Each OC-12 node can provision the same STS-1 time slots as other OC-12
nodes to drop to the OC-3 shelf (to share STS-1s among several OC-3 shelves) or
the OC-12 node can provision different STS-1s at different sites. When ring (0x1)
is used, the OC-12 ring passes the contents of these STS-1 time slots between
the low-speed OC-3/IS-3 lines and OC-12 high-speed lines without terminating
them or performing any path protection switching on them. Up to four OC-3 rings
can be supported in this fashion by an OC-12 ring to maximize the OC-12
bandwidth utilization. This allows access to any and all VT1.5 signals at an OC-12
site. Since the high-speed signals from the OC-3 ring(s) are sent as two copies
(one clockwise, the other counterclockwise) on the OC-12 ring, the OC-12 ring
capacity is limited to the OC-12 line rate.
The OC-3/IS-3 lines between an OC-12 node and an OC-3 node connected in a
ring 0x1 fashion behave like the OC-3 lines between the nodes on an OC-3 ring
and do not perform line level protection switching. Instead, the OC-3 shelves
perform the normal path protection switching functions.
Some points to note for this application are:
■ Ring (0x1) can be thought of as a "ring on ring" with many of the
characteristics of a single ring.
■ Pass-through cross-connections may be required at the VT and STS level.
■ The OC-3 ring can be composed of any three STSs in the OC-12.
■ An OC-12 STS may be the first STS in one extension, the second STS in
another, and the third STS in another.
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