core network of a large carrier; it supports longer distances, 10 and 40 Gbit/s, and there is a possibility of supporting pure transparent branching via a fixed OADM. Tunable OADM is also supported, in order either to drop a few channels in an interme- diate site of a point-to-point link or to build optical transparent rings on long distances. Both optical channel and optical multiplex section (OMS) protections are supported. Finally, the third system is a long-haul system also proposed for particularly high traffic regional areas. 6.3.3 Design of Ultra-Long-Haul Transmission Systems If it is needed to design a DWDM system with a reach far greater than the number reported in Table 6.5, refining the design cannot help. Nevertheless, the reach limitations of long-haul systems can be overcome by the com- bined use of EDFA and Raman amplification. There are several possible architectures to use distributed or concentrated Raman ampli- fication to design ultra-long-haul systems, each of which has its own design rules. Raman amplification, can be used to provide distributed amplification as a complement to lumped EDFAs in the hybrid approach or all Raman amplification can be used, poten- tially both distributed and lumped. TABLE 6.6 Characteristics of Realistic Long-Haul Systems Designed for Different Applications Channels Number of Channel Reach (Only Optical Application Speed Channels Spacing EDFAs) Bands OADMs Notes Real Estate Long haul 100 Mbit/s Up to 128 50 GHz 1200 km From 4 to 40 1 + 1 OChP 1 standard rack-64 Regional wavelength per channels 10 Gbit/s Long haul 10 or 40 Up to 96 @ 10 50 GHz 2500 km @ Fixed OADM Line dispersion Rack dimensions: Gbit/s Gbit/s 10 Gbit/s for passive compensation Height: 2200 mm Up to 80 @ 40 Gbit/s 1600 km @ branching per band Width: 600mm Gbit/s in the 200 GHz 40 Gbit/s configuration dispersion Depth: 300 mm C-band Wavelength compensation Gbit/s Selective 1 +1 OCH 10G/40G mix Switch protection supported (WSS)-based technology protection Long haul 10 or 40 192 @ 10 25 GHz 5000km @