th in Chapter 3 the low-loss window of optical fiber between 1,528 and 1,560 nm. Both the S/DMS TransportNode OC-12 TBM and OC-48 product lines permit wide- band WDM implementations using currently available wavelength options. An example bidirectional wideband WDM configuration based on the TBM's 1,310- and 1,550-nm wavelengths appears in Figure 3-61. Narrowband WDM As with wideband WDM, the narrowband method provides a twofold increase in fiber span capacity. It employs two low-loss wavelengths, typically 1,533 and 1,557 nm. S/DMS TransportNode's OC-48 and OC-192 product lines both offer wavelength options that fully support bidirectional narrowband WDM, as depicted in Figure 3-62. On long-haul routes where system reach is an important consideration, narrowband WDM is usually a better choice relative to wideband WDM. In addition, narrowband WDM offers total compatibility with Nortel's S/DMS TransportNode's optical amplifier product line on both single-hop and mul- tihop OC48/192 routes. This means the economic advantages of expanded fiber capacity and extended reach can be achieved in the same application. Outside Plant Figure 3-61 OC-12 TBM shelves 11+12 Mixed deployed in a Tributaries Mixed bidirectional Single-Fiber Tributaries OC-12 Bidirectional Channel wideband WDM S/DMS TransportNode Wave Division Wave Division S/DMS TransportNode application. OC-12 TBM Multiplex Coupler Multiplex Coupler OC-12 TBM 11 = 1310 nm 12 = 1550 nm 11+12 = 1310 + 1550 nm Outside Plant Figure 3-62 Nortel's S/DMS 11+12 Mixed TransportNode Mixed Tributaries Tributaries OC-48/192 network Single-Fiber OC-48/192 Bidirectional Channel elements deployed in S/DMS TransportNode Wave Division Wave Division S/DMS TransportNode a typical bidirectional OC-48/192 Multiplex Coupler Multiplex Coupler OC-48/192 narrowband WDM Network Element Network Element application. 11 = 1310 nm 2 = 1550 nm 11-12 = 1310 + 1550 nm Traditional SONET Architectures Dense WDM (DWDM) Advanced DWDM technology employs many wavelengths to increase fiber span capacity.