As such, 1+1 protection doubles fiber requirements but halves
power budgets (distance reach). Alternatively, 1:1 or 1:N shared protection can improve
fiber efficiency and span reach. These setups use active switching and rapid protection
signaling and allow for lower priority users to share idle protection fibers. However,
there are no standards for optical fiber/span protection and most offerings are vendorproprietary.
Albeit nonselective at the service layer, fiber protection can significantly
lower higher-layer protection costs.
Fixed Add-Drop Rings As point-to-point DWDM systems proliferated, the next logical
step for carriers was the extension of wavelength channels across fiber rings, i.e., secondgeneration
DWDM [3]. In essence, the goal was to leverage entrenched ring-fiber plants
in incumbent carrier networks. This evolution yielded transparent optical add-drop
multiplexer (OADM) designs, as shown in Figure 8.3, which implemented all-optical
wavelength bypass at intermediate ring sites, creating multihop lightpath connections.
OADM designs proved much more cost-effective than back-to-back OTM configurations,
as they obviated the need for service-specific electronics to retransmit bypass channels.
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