  We test the concept of extended channel probing in an Optical Spectrum as a
Service scenario in coherent optimized flex-grid long-haul and 10Gbit/s OOK
optimized 100-GHz fixed-grid dispersion-managed legacy DWDM networks. An
estimation accuracy better than +/- 0.1dB in GSNR implementation margin is
obtained for both networks by using flexible coherent transceivers on
lightpaths up to 822km on regional haul legacy network and up to 5738km on a
long-haul network. We also explain, how to detect the operation regime of the
channel by analyzing the received GSNR results from constant power spectral
density (PSD) probing mode and constant signal power probing mode
