2). Moreover, intense market competition continues to drive price reductions,
about 20 percent per year [2], offering genuine prospects for capital (CAPEX)
and operational (OPEX) expense reduction. These new paradigms are detailed in the
following sections.
Point-to-Point DWDM Transport The first commercial DWDM deployments took place
in the mid-1990s and were primarily aimed at point-to-point ???fiber-relief??? on congested
long-haul spans, i.e., first-generation DWDM (see Figure 8.3) [3]. These build-outs used
optical terminal multiplexer (OTM) systems to improve cost-per-bit-per-mile by exploiting
the multichannel transmission/amplification economics of DWDM. Although these
systems were very costly at the time, they saw strong uptake due to the large amortization
base of the long-haul sector. Over the years, more cost-optimized OTM renditions
were also evolved for the metro/regional sectors in order to relieve congestion on heavily
Figure 8.3 Optical network evolutions and optical network elements (ONE) designs
Reconfigurable OADM,
Optical Cross-connect (OXC)
Third-Generation DWDM
Dynamic optical DWDM
ring-mesh topologies
Static Optical Add-Drop Mux
Second-Generation DWDM
Static optical DWDM
linear/ring topologies
??? Developed mid-1990s
??? Point-to-point fiber relief
??? Staged filters, amplifiers
??? Short-reach client interfaces
??? Up to 160 wavelengths/fiber
Optical Terminal Multiplexer
SONET
OC-48/192
DWDM
SONET
OC-3/12
ADM
Point-to-point capacity
expansion
Laser
transponders
Post-amp
Modular
filter
OXC
SPRING
(32-128 ?»)
Pre-amp
Demux
Post-amp
Mux
??? Ring, multiring, mesh topologies
??? Dynamic switching, add/drop
??? Power balancing / AGC
??? Intelligent control plane (GMPLS)
??? Dedicated/shared protection,
restoration
Pre-amp Post-amp
Optical
fabric
??? Mid-1990s-early 2000s
??? Static ring, multiring
??? Fixed routing/channel assignment
??? Manual provisioning, VOA tuning
??? 1+1 UPSR channel protection
Manual
patching
Laser
transponders
Tunable laser
transponders
Tunable filters
Fixed
OADM
DCS
UPSR ring
(16-32 ?»)
ROADM
Client
interfaces
First-Generation DWDM
x
x
Fiber and WDM 203
loaded interoffice fiber (IOF) spans.
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