6.2 Optical Transport Network 389 All-optical Optical layer Optical Broadband SONET layer Wideband Narrowband Wavelength, waveband, fiber grooming STS-48 grooming DS3 grooming DS1 grooming DS0 grooming Figure 6.9 Different types of crossconnect systems. traffic at the DS1 level. At the bottom of the hierarchy is a narrowband DCS, which grooms traffic at the DS0 level. Next up is a wideband DCS, which grooms traffic at DS1 rates, and then a broadband DCS, which grooms traffic at DS3/STS-1 rates. These DCSs typically have interfaces ranging from the grooming rate to much higher- speed interfaces. For instance, a wideband DCS will have interfaces ranging from DS1 to OC-12, while a broadband DCS will have interfaces ranging from DS3 to