Fiber and WDM 207
Another challenge in all-optical rings is optical-layer performance monitoring.
Currently, there are no standards in this area, and most vendors provide their own proprietary
schemes such as fiber/wavelength powers, optical SNR, and so on. However, it
is well-understood that these offerings can only detect hard faults??”not degenerative
conditions??”because they lack the bit-level resolution of SONET/SDH. Regardless,
these features still suffice for ROADM applications [3]. For example, trunk power
monitoring can rapidly isolate hard failures (fiber cuts and node faults) in order to
support protection switching. Note that transparent ROADM rings use more specialized
outband control setups with separated data and control planes; most vendors
use the 1510 nm optical supervisory channel (OSC) wavelength for control signaling.
Nevertheless, there are no standards for OSC signal formats and vendors either
use SONET/SDH or Ethernet framing. In general, this yields lower levels of vendor
interoperability.
ROADM rings can easily implement UPSR protection. In addition, these nodes can
also facilitate more advanced shared protection ring (SPRING) schemes [4].
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