Detailed characteristics of the modulational instability oscillation in a single mode optical fiber ring cavity are described. There is a clear threshold pump power for the oscillation, and stable oscillation can be achieved with a proper synchronization. It is shown that phase coherence among pump, Stokes, and anti-Stokes consistent with the propagation of higher order solitons plays an important role in the generation of MI gain. A noninstantaneous response of the nonlinear index (self-induced Raman gain) competes with the modulational instability gain and produces an asymmetry in the spectrum of the Stokes and the anti-Stokes pulses. When a strong pump depletion occurs, the modulational instability cannot be achieved, and the Stokes pulse forms unaided into a single soliton.