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We experimentally study limitations imposed by fiber nonlinearities to achieve long repeaterless sections in a 25-GHz spaced metropolitan WDM network. We show that in a high spectral density transmission system using nonzero dispersion-shifted fiber (NZ-DSF) as transmission medium, stimulated Brillouin scattering (SBS) is not the major limiting nonlinearity. Thus, the choice of transmitter is not dictated by its linewidth and high performance DFB fiber lasers should be seriously taken into consideration. We experimentally verify that in metropolitan areas distributed Raman amplification is necessary to lengthen the repeaterless sections.