ion of layer(s) (SONET/ATM) will ease the job of network management and will be cost effective. 2 The erbium-doped fiber amplifier (EDFA) is the most deployed fiber amplifier as its amplification window coincides with the third transmission window of silica-based optical fiber. Next Generation Mobile Communications Ecosystem SONET/SDH SONET/SDH DWDM ring OC-192 ring OC-192 ring Figure 7.11 SONET DWDM hybrid architecture DWDM systems can be planned for a large number of channels, however, pay-as-you-grow strategy can be employed and channels added according to demand. The amplifier distance and overall power budget of the system needs to be calculated for the final number of channels from the beginning. 7.4.1.4 CWDM Coarse WDM (CWDM) is a standard by ITU-T called G.694.2 where the WDM channel spacing is increased to 200 GHz. It typically supports 16 or less channels for metro networks. The main characteristic of the ITU G.694.2 CWDM standard is that the signals are not spaced appropriately for amplification by EDFAs. This therefore limits the total CWDM optical span to somewhere near 60 km for a 2.5 Gbps signal, which is suitable for use in metropolitan applications. The relaxed optical frequency stabilization requirements allow the associated costs of CWDM to approach those of non-WDM optical components. 7.4.1.5 NGSDH Although SDH has established itself as the predominant optical fiber transmission transport technique, the increased amount of data traffic has revealed its weaknesses. The SDH does not provide efficient transport of packet-based traffic and to combination of TDM and IP traffic. One viable solution came in the form of Next Generation SDH that enables the delivery of both TDM and packet based services in a cost effective manner. NGSDH enables Ethernet transport that is referred to as Ethernet over SONET/SDH. NGSDH comprises of three traffic concatenation strategies: Virtual Concatenation (VCAT) allows for a more arbitrary assembly of lower order multiplexing containers, building larger containers of 