 This limits the total CWDM optical span to somewhere near 60 km for a 2.5 Gbit/s 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.CWDM is being used in cable television networks, where different wavelengths are used for the "downstream" and "upstream" signals.