With add-drop traffic averaging almost 25 percent per site these ???transponderless???
designs enable sizeable CAPEX reduction, particularly at higher 10 Gbps speeds.
Static OADM nodes augment basic OTM designs by adding wavelength/wavelength
band bypass-and-add-drop filters (see Figure 8.3). These designs lower insertion losses
for transit channels (by about 2 dB per node) and deliver commensurate increases in
ring diameters. Most OADM designs are also complemented with pre- and post-amplifiers
in order to handle transmission and nodal losses, respectively. Nevertheless, fixed
OADM rings have sizeable manual overheads (OPEX) and require skilled technical
staff. Careful preplanning is required to ensure wavelength connectivity for all node
demands, i.e., static routing and wavelength assignment (RWA) [1]. In addition, complex
amplifier preengineering is needed to maintain lightpath signal-to-noise ratios (SNR).
Finally, careful power-balancing is also required between bypass and add-drop channels
within an OADM to ensure proper EDFA operation. This is commonly done using
advanced EDFA gain equalization features and placing a variable optical attenuator
(VOA) along channel paths.
Pages:
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513