he grid by extending the upper or lower bounds or by spacing the wavelengths more closely, typically at 50 GHz, to double the number of channels. Figure 5-28 depicts the usage of the fre- quency bands in 8-, 16-, 24-, or 32-lambda systems. However, interworking will suffer if vendors utilize variants of the basic standard. Dense Wavelength Division Multiplexing (DWDM) Systems Frequency Wavelength Frequency Wavelength Frequency Wavelength Figure 5-26 (THz ¹ (nm2) (THz) (THz) ITU-T G.692 grid. 196.1 1528.77 194.6 1540.56 193.1 1552.52 196.0 1529.55 194.5 1541.35 193.0 1553.33 195.9 1530.33 194.4 1542.14 192.9 1554.13 195.8 1531.12 194.3 1542.94 195.8 1554.94 195.7 1531.9 194.2 1543.73 192.7 1555.75 195.6 1532.68 194.1 1544.53 192.6 1556.56 195.5 1533.47 194.0 1545.32 195.5 1557.36 195.4 1534.25 193.9 1546.12 192.4 1558.17 195.3 1535.04 193.8 1546.92 192.3 1558.98 195.2 1535.82 193.7 1547.72 192.2 1559.79 195.1 1536.61 193.6 1548.51 192.1 1560.61 195.0 1537.40 193.5 1549.32 192.0 1561.42 194.9 1538.19 192.4 1550.12 191.9 1562.23 194.8 1538.98 193.3 1550.92 191.8 1563.05 194.7 1539.77 193.2 1551.72 191.7 1563.86 1THz = Terahertz 2nm = Nanometer ITU Grid Reference Point (193.1 THz) Figure 5-27 ITU-T grid on the electromagnetic Channel 60 Channel 20 spectrum. 199.0 196.0 195.0 194.0 193.0 192.0 191.0 190.0 186.0 f (THz) 1 (nm) S Band OA C Band OA L Band OA Flat Gain Region Flat Gain Region Flat Gain Region DWDM systems with open interfaces give carriers the flexibility to sup- port SONET/SDH, asynchronous protocols (for example, DS3), ATM, Frame Relay, and other protocols over the same fiber pair. Open systems also elim- inate the need for additional high-performance optical transmitters to be added to a network when you need to interface with specific protocols (see Figure 5-29). Open WDM systems enable service providers to adapt new technologies to the network through the use of off-the-shelf, relatively Chapter 5 ITU-T Wavelength Grid Number of Wavelengths in Application Figure 5-28 with 100-GHz Spacing Grid-point f