Optical buffers are key components in optical packet switching network systems that prevent packet collision along the same virtual path and wait for header processing time. An optical tunable delay line using a fiber ring with an AO frequency shifter and an erbium-doped fiber amplifier (EDFA) presents the benefit of stable operation without unexpected oscillation. Using numerical simulation, this study clarifies the delay line's power distribution and SNR degradation. The longest delay time of 200 times the packet length can be achieved for a 10Gbit/s data packet.